Glossary of landforms

A glossary of landforms is a reference compilation providing definitions for the specialized terms describing the natural features and formations that constitute the terrain of the Earth's surface, including major types such as mountains, hills, plateaus, and plains, as well as minor features like canyons, valleys, and basins.^[1][2] These landforms result from a combination of geological processes, including tectonic plate movements that uplift and fold the crust to form mountains and hills, and erosional forces from water, wind, and ice that carve valleys and canyons over millions of years.^[1][3] Such glossaries serve as essential tools in geomorphology—the scientific study of landform formation and evolution—and related disciplines like soil science and environmental mapping, standardizing terminology to facilitate accurate description, analysis, and classification of landscapes worldwide.^[4][5] For instance, authoritative glossaries often include terms for depositional features like alluvial fans, which are fan-shaped sediment accumulations formed where streams emerge from mountains onto plains, and erosional remnants such as buttes, isolated steep-sided hills capped by resistant rock layers.^[6][7] By encompassing both broad categories and specific subtypes, these resources support research into landscape dynamics, hazard assessment, and conservation efforts, reflecting the ongoing interplay of constructive and destructive forces that continually reshape the planet's surface.^[3][8]

Introduction

Definition of Landforms

A landform is a natural feature of the Earth's solid surface, comprising terrain elements shaped by endogenous and exogenous geological processes. Endogenous processes arise from internal Earth dynamics, such as tectonic uplift and volcanism, while exogenous processes involve external agents like weathering, erosion, and deposition that modify the surface. These features encompass a wide range of scales, from microscale elements like ripples and small gullies, which measure mere centimeters to meters, to macroscale structures such as mountain ranges and continental plains spanning thousands of kilometers.^[9][10][11] Key attributes of landforms include their elevation relative to sea level, slope gradient, topographic relief (the vertical difference between peaks and valleys), and material composition, which may consist of bedrock, unconsolidated sediments, or glacial ice. These characteristics determine the form, stability, and evolution of landforms, influencing how they interact with environmental processes. For instance, steep slopes with high relief often result from rapid tectonic activity, whereas low-relief plains form through prolonged sedimentary deposition. Elevation and slope also affect local climate and hydrology, further shaping landform development over time.^[10][11][12] The concept of landforms evolved within 19th-century geomorphology, a field formalized by scholars like William Morris Davis, who introduced the cycle of erosion in the 1890s to describe how landscapes progress from youthful, rugged forms to mature, subdued ones through denudation. Davis's work, building on earlier observations of terrain evolution, emphasized the interplay of structure, process, and time in landform genesis, laying the groundwork for systematic study of Earth's surface features. This historical framework shifted geomorphology from descriptive cataloging to process-oriented analysis, influencing modern understandings of landform diversity.^[13][14]

Classification of Landforms

Landforms are categorized using several primary schemes to facilitate systematic study and mapping in geomorphology, including classifications by genetic process, morphology, scale, and material composition. These approaches provide frameworks for understanding the origins, forms, sizes, and substances of Earth's surface features, enabling comparisons across diverse landscapes. Genetic classification distinguishes between processes driven by internal Earth forces and those influenced by external agents, while morphological schemes focus on physical attributes like shape and curvature. Scale-based systems organize landforms hierarchically by size, and material classifications differentiate based on the composing substances, such as rock types or sediments. Together, these methods underpin much of modern geomorphological analysis, though they are often integrated for comprehensive assessments.^[15] The genetic classification scheme divides landforms primarily into endogenous and exogenous categories based on the dominant formative processes. Endogenous landforms result from internal geological forces, such as tectonic movements that create mountain ranges through uplift or folding, and volcanic activity that builds features like cones and plateaus via magma extrusion.^[16] In contrast, exogenous landforms arise from surface processes, including weathering that breaks down rock materials, erosion by water, wind, or ice that sculpts valleys and canyons, and deposition that forms plains and deltas through sediment accumulation.^[16] This binary framework, rooted in the interplay of internal and external dynamics, highlights how endogenous processes establish broad structural relief, which exogenous agents then modify over time.^[11] Morphological classification emphasizes the physical form and relief of landforms, often using attributes like topographic position and curvature profiles to delineate categories. Landforms are grouped by form into positive features (elevated relative to surroundings, such as ridges and hills), negative features (depressed, like valleys and basins), and flat or planar areas (plains with minimal relief).^[17] Profile curvature further refines this by identifying concave shapes (where slopes curve inward, promoting convergence of surface flow, as in valley bottoms) and convex shapes (curving outward, facilitating divergence, typical of hilltops).^[18] These principles allow for quantitative assessment of terrain complexity, with relief (vertical difference) serving as a key metric to differentiate low-relief plains from high-relief mountains.^[17] Scale-based classification organizes landforms hierarchically to reflect their spatial extent and nested relationships, typically dividing them into orders from global to local features. First-order landforms encompass large-scale structures like continents and ocean basins, shaped by plate tectonics over millions of years.^[11] Second-order features include regional elements such as mountain ranges, plateaus, and broad plains, which modify the first-order relief through uplift or subsidence.^[11] Third-order landforms represent finer-scale details, like individual valleys, dunes, or stream channels, influenced by localized erosion and deposition.^[11] This hierarchical approach aids in analyzing how smaller features interact within larger ones, providing a multiscale perspective on landscape evolution.^[19] Classification by material composition categorizes landforms according to their primary substances, which influence stability and further modification. Common groups include unconsolidated mineral materials (such as alluvium in river plains or colluvium on slopes), organic deposits (like peat in wetlands), consolidated rocks (igneous, sedimentary, or metamorphic forming cliffs and outcrops), and ice (glaciers and permafrost features).^[19] This scheme is particularly useful in soil science and engineering, as material properties determine susceptibility to weathering or erosion; for instance, unconsolidated sediments erode more readily than consolidated bedrock.^[19] Since the 1990s, modern approaches to landform classification have increasingly integrated geographic information systems (GIS) and remote sensing technologies, enabling automated, large-scale mapping with high precision. GIS facilitates the analysis of digital elevation models (DEMs) to compute metrics like slope, curvature, and topographic position index (TPI), automating the delineation of morphological classes across vast areas.^[17] Remote sensing, through satellite imagery and LiDAR, provides detailed data on surface composition and relief, supporting genetic and material classifications by integrating spectral and topographic information.^[20] These tools have revolutionized geomorphology by allowing dynamic updates to classifications and revealing subtle patterns invisible to traditional field surveys, as evidenced in global DEM-based studies.^[20]

Landforms by Formation Process

Aeolian Landforms

Aeolian landforms are surface features shaped primarily by the erosive, transporting, and depositional actions of wind, predominantly in arid, semi-arid, and coastal environments where vegetation is sparse and wind velocities are high enough to mobilize sediment. These processes involve deflation, which removes loose particles from the surface; abrasion, where wind-borne sand grains scour exposed rock; and deposition, where transported materials accumulate into new forms. Aeolian activity is most pronounced in regions with annual precipitation below 250 mm, allowing wind to dominate over water in landscape evolution. Unlike fluvial processes that rely on flowing water for sediment transport, aeolian mechanisms operate through saltation, suspension, and creep of particles, often creating streamlined or mound-like features aligned with prevailing wind directions.^[21] Ventifacts are individual rocks or boulders that have been sculpted by wind abrasion, resulting in polished, faceted surfaces, pits, grooves, or etched patterns. Formation occurs when wind-driven sand grains impact exposed rock at low angles, preferentially eroding softer minerals and creating facets perpendicular to the dominant wind direction; this process can take thousands of years in hyper-arid settings. The resulting shapes, often triangular or pyramidal, serve as paleo-wind indicators, with facets facing upwind. Examples include ventifacts in Death Valley National Park, California, where quartzite and basalt rocks exhibit deep fluting from persistent westerly winds.^[21][22][23] Yardangs are elongated, streamlined ridges or hills carved from bedrock or semi-consolidated sediments by a combination of wind deflation and abrasion. They form in areas of alternating resistant and erodible layers, where wind removes softer material, leaving isolated, boat-shaped protrusions aligned parallel to the prevailing wind, with lengths up to several kilometers and heights from meters to tens of meters. Abrasion by saltating sand grains sharpens the upwind (stoss) side into a blunt prow, while deflation hollows the downwind (lee) side. Prominent examples occur in the Lut Desert of Iran, where yardangs rise up to 100 meters and record wind regimes over millennia.^[21][24][24] Sandhills, also known as vegetated sand dunes, are accumulations of wind-blown sand that form low-relief mounds or ridges, often stabilized by sparse vegetation such as grasses that trap and anchor the sediment. They develop through episodic wind deposition in inland arid zones, where sand is transported by saltation and accumulates in areas of reduced wind speed, such as behind obstacles; parabolic subtypes are common, with trailing arms shaped by blowouts in the vegetation cover. Unlike active transverse dunes, sandhills persist due to plant roots binding the sand, preventing further mobilization. The Nebraska Sandhills in the United States exemplify this, covering over 50,000 square kilometers as the largest sand dune formation in the Western Hemisphere, formed from glacial outwash sands during the Pleistocene and now supporting ranchland.^[21][21] Dry lakes, or playas, are flat, basin-like depressions in arid interiors that periodically fill with shallow water from infrequent rains or groundwater, subsequently evaporating to leave a salt-encrusted surface of wind-deposited evaporites. Formation involves tectonic or erosional basin development followed by evaporation concentrating dissolved minerals into halite, gypsum, or other salts, which wind then redistributes as fine aerosols or deflation lag. These features act as sources and sinks for aeolian sediment, with salt crusts inhibiting erosion until cracked by drying. The Bonneville Salt Flats in Utah represent a classic playa, spanning 100 square kilometers and formed from the prehistoric Lake Bonneville's evaporation around 10,000 years ago, with wind enhancing the flat, polygonal crust patterns.^[25][26][27]

Coastal and Oceanic Landforms

Coastal and oceanic landforms arise from the interaction of marine processes such as wave action, tidal movements, ocean currents, and sediment transport at the land-sea interface and on the seafloor. These features form through erosion, deposition, and biogenic activity, shaping shorelines and deep-ocean topography over geological timescales. Erosional processes dominate in high-energy environments, carving cliffs and platforms, while depositional mechanisms build bars and plains from accumulated sediments. Oceanic landforms extend beyond the coast to include vast submarine structures influenced by turbidity currents and slow sedimentation rates.^[28][29][30] Atoll
An atoll is a ring-shaped coral reef that encircles a central lagoon, typically forming around subsiding volcanic islands in tropical oceans. Formation begins with fringing reefs growing upward on volcanic foundations as the underlying crust subsides due to tectonic forces, allowing corals to maintain pace with sea-level changes and eventually forming a barrier reef before the island erodes away completely. This subsidence theory, originally proposed by Charles Darwin, explains the evolution from fringing reef to atoll over millions of years, though modern models incorporate differential dissolution and karstification during glacial periods as additional factors. Atolls, such as those in the Pacific's Tuamotu Archipelago, support diverse marine ecosystems but are vulnerable to sea-level rise. Coral reefs, including atolls, represent biogenic landforms driven by symbiotic algae and coral polyps.^[31][32][33] Tombolo
A tombolo is a depositional coastal landform consisting of a narrow bar or spit of sand, gravel, or shingle that connects an offshore island to the mainland or another island, effectively bridging the two landmasses. It forms through longshore drift, where waves refract around the island and deposit sediment in the sheltered zone between the island and shore, gradually building the bar over thousands of years. The process requires a balance of wave energy that promotes deposition rather than erosion, often in areas with prevailing currents aligning sediment transport. Notable examples include the tombolo at Mont Saint-Michel in France and Stockton Island in Wisconsin's Apostle Islands National Lakeshore, where glacial till and wave action have shaped the feature since the end of the last Ice Age around 6,000 years ago.^[34][35] Wave-cut platform
A wave-cut platform, also known as a shore platform, is a gently sloping, flat expanse of eroded bedrock extending seaward from the base of a coastal cliff, formed by the persistent abrasive and hydraulic action of waves. Waves attack the cliff base, undercutting it through processes like corrosion and attrition, causing rockfalls that expose the platform; over time, the platform widens as continued wave erosion smooths the surface to near the low-tide level. These platforms typically range from tens to hundreds of meters in width and are common on rocky coasts with resistant lithology, such as limestone or sandstone. In Ireland's coastal regions, for instance, wave-cut platforms at low tide reveal evidence of long-term marine erosion rates influenced by storm frequency and tidal range.^[36][37] Abyssal plain
An abyssal plain is a vast, flat to gently undulating region of the deep ocean floor, typically at depths of 3,000 to 6,000 meters, covered by thick layers of fine-grained sediments that mask underlying topography. These plains form primarily through the deposition of terrigenous and biogenic particles transported by turbidity currents—underwater avalanches of sediment-laden water that channel material from continental margins via submarine canyons to the deep sea. Sedimentation rates are low, often less than 1 cm per 1,000 years, resulting in plains spanning hundreds of thousands of square kilometers, such as the Sohm Abyssal Plain in the North Atlantic. Turbidity currents deposit graded beds of silt and clay, smoothing the seafloor and burying volcanic or tectonic features over millions of years.^[30][38][39]

Cryogenic Landforms

Cryogenic landforms, also known as periglacial landforms, are geomorphic features that develop in cold, non-glacial environments characterized by intense freeze-thaw cycles, permafrost, and cryoturbation processes. These landforms arise primarily in high-latitude or high-altitude regions where mean annual temperatures remain below 0°C, leading to the seasonal freezing and thawing of the active layer above permafrost. Unlike glacial landforms shaped by moving ice masses, cryogenic features result from the expansion of water upon freezing, ground ice segregation, and solifluction on slopes, often in areas marginal to glaciers.^[40] The formation of cryogenic landforms is driven by thermal contraction cracking, frost heaving, and the differential movement of soil and rock under periglacial conditions. Permafrost, defined as ground that remains at or below 0°C for two or more years, serves as a foundational element, influencing water availability and soil stability. These processes create distinctive patterns and structures that reflect the interplay of climate, substrate, and topography, with examples widespread in the Arctic, Antarctic dry valleys, and alpine zones.^[41][42]

Pingo

A pingo is an ice-cored, dome-shaped hill that forms in permafrost regions through hydrostatic pressure buildup in a closed-system talik, where unfrozen water beneath the permafrost freezes upward, doming the overlying sediments. These features typically range from 2 to 70 meters in height and up to 1 kilometer in diameter, with the ice core comprising 80-90% of the volume in mature pingos. Formation begins in lowlands or drained lake basins where segregation ice accumulates, often cracking the surface to form a summit crater upon reaching full growth. Open-system pingos, less common, develop on slopes where artesian groundwater pressure forces ice lens growth. Pingos are diagnostic of continuous permafrost zones and are prevalent in northern Alaska, Canada, and Siberia, serving as indicators of past hydrological conditions.^[43][40][44]

Thermokarst

Thermokarst refers to irregular landforms, such as depressions, ponds, and lakes, created by the thawing of ice-rich permafrost, leading to thermal erosion, subsidence, and collapse of the ground surface. The process is initiated when the active layer thickens due to climatic warming or disturbance, melting massive ice wedges or lenses and causing rapid vertical and lateral retreat of thaw margins. Common in yedoma deposits with high ice content (up to 80% by volume), thermokarst features evolve into kettles, alases (large thaw depressions), or connected drainage networks, altering hydrology and releasing stored carbon. These landforms are widespread in Arctic lowlands, like the North Slope of Alaska, where they cover up to 20% of the landscape in some areas.^[42][45][46]

Rock Glacier

A rock glacier is a tongue- or lobe-shaped mass of coarse, angular rock debris that advances downslope through the creep of interstitial ice or a buried ice core, typically at rates of 0.1 to 2 meters per year. Formation occurs in cirque headwalls or talus slopes where debris accumulates over snow or glacier ice, insulating it and promoting permafrost development, which then deforms under gravity to drive slow flow. Distinguished by longitudinal ridges, transverse furrows, and steep fronts (often 20-30°), rock glaciers contain 20-50% ice by volume and can extend several kilometers in length. They are common in mid-latitude mountains, such as the Sierra Nevada and Rocky Mountains, where they persist longer than glaciers due to debris insulation.^[47][48][49]

Earth Hummocks

Earth hummocks, also called turf hummocks or thufur, are small, rounded mounds of soil and vegetation, typically 20-50 cm high and 0.5-2 m in diameter, formed by repeated frost heaving and cryoturbation in fine-grained, moisture-rich substrates. Development involves the freezing of water in the active layer, which expands to uplift soil into domes, followed by downslope movement and sorting of particles during thaw, creating involuted boundaries and central depressions. These features require seasonal freeze-thaw cycles with adequate water supply, often in flat or gently sloping terrain underlain by discontinuous permafrost or in non-permafrost periglacial settings. Earth hummocks dominate patterned ground in subarctic and alpine tundra, such as in Alaska and the Canadian Rockies, influencing microtopography and drainage.^[50][51][52]

Erosion Landforms

Erosion landforms arise from the processes of detaching, transporting, and removing earth materials, primarily through agents such as water and gravity, which sculpt the landscape by lowering elevations and exposing underlying structures. These features differ from weathering landforms, where material breakdown occurs in situ without significant transport; erosion emphasizes the relocation of sediments, often resulting in sharp relief and minimal vegetation cover. In arid and semi-arid regions, differential erosion plays a key role, as resistant rock layers protect softer underlying materials, creating isolated elevations and incised valleys.^[53] The formation of erosion landforms is driven by episodic events like heavy rainfall, which accelerate sediment removal, and long-term tectonic uplift that exposes rocks to denudation. Rates of erosion can reach 2.5 cm per year in susceptible areas, influenced by rock type, slope angle, and climate. These landforms provide insights into geological history, revealing ancient sedimentary layers through progressive carving.^[54] Badlands are intensely eroded landscapes characterized by steep slopes, sharp ridges, and sparse vegetation, typically developed on soft, poorly consolidated sedimentary rocks such as shales and mudstones. Formation occurs through rapid weathering and mass wasting followed by fluvial transport during infrequent but intense thunderstorms, which can erode up to 2.5 cm of material annually. In Badlands National Park, South Dakota, the White River Group—comprising formations like the Brule and Sharps—underlies these features, with erosion exposing Cretaceous shales below and creating pinnacles, gullies, and barren tables. The low annual precipitation (about 43 cm) and extreme temperatures exacerbate soil instability, limiting plant cover and sustaining high erosion rates.^[54] Mesa refers to an isolated, flat-topped hill or mountain with steep escarpments on at least one side, formed by the erosion of surrounding softer strata while a resistant caprock, such as sandstone, preserves the summit. These landforms evolve from broader plateaus through differential erosion, where lateral cutting by streams and weathering exposes vertical cliffs. Mesas are prevalent in the southwestern United States, including Colorado and Utah, with Grand Mesa in Colorado exemplifying the type at over 1,300 square kilometers and elevations exceeding 3,350 meters. The caprock's durability slows further dissection, maintaining the table-like profile over millions of years.^[55] Butte is a smaller erosional remnant than a mesa, consisting of a steep-sided, flat-topped hill typically under 300 meters tall and 300 meters wide at the base, resulting from advanced erosion that isolates sections of a mesa. Like mesas, buttes feature a protective hard caprock overlying erodible layers, but continued removal of surrounding material narrows the summit to a narrow platform. This progression highlights erosion's role in reducing landform scale, as seen in formations across Arizona and New Mexico where wind and water preferentially attack weaker beds. The distinction from mesas lies primarily in size and complete encirclement by cliffs, emphasizing ongoing landscape dissection.^[55] Canyon denotes a deep, narrow valley with steep, often vertical walls, carved primarily by persistent downcutting and lateral erosion that removes vast volumes of rock. These landforms expose stratigraphic sequences, with depths reaching over 1,800 meters in examples like the Grand Canyon, where uplift facilitated incision through layered sedimentary rocks over five million years. Canyons form in response to base-level lowering, with intermittent streams accelerating headward erosion to create V-shaped profiles. Many fluvial canyons, such as those along the Colorado River, illustrate river-specific incision but share general traits of rapid sidewall retreat and sediment export.^[56]

Fluvial Landforms

Fluvial landforms are geomorphic features primarily shaped by the action of flowing water in rivers and streams, encompassing processes of erosion, sediment transportation, and deposition. These landforms develop in dynamic river systems where water velocity, sediment load, and channel gradient interact to sculpt the landscape. Stream erosion is often the dominant geomorphic agent in fluvial environments, carving valleys and creating distinctive channel patterns over time.^[57] Fluvial processes are most active in humid to semi-arid regions but can occur in various climates, influencing both upland and lowland terrains.^[58] Erosion in fluvial systems occurs through hydraulic action, abrasion, and solution, where faster-moving water on outer bends or steeper gradients removes bedrock and soil. Transportation involves the movement of suspended load, bedload, and dissolved materials downstream, with deposition happening when flow velocity decreases, such as at channel confluences or base level changes. These processes create a spectrum of landforms, from incised channels to expansive depositional plains, reflecting the river's adjustment to its energy regime. Representative examples include sinuous channels, abandoned loops, fan-shaped spreads, and abrupt drops, each illustrating specific aspects of fluvial dynamics. Meanders are sinuous curves in a river channel that form in low-gradient zones where streams transport fine sediments, with lateral erosion dominating on the outer concave bank due to higher velocity and helical flow patterns. Deposition occurs on the inner convex bank, building point bars of sand and gravel that promote further meander migration downstream. Over time, meanders can enlarge and migrate, elongating the channel and increasing the river's path length compared to a straight-line distance.^[59] This process is evident in many mature rivers, such as those in the Mississippi River basin, where meander growth reflects the balance between erosive power and sediment supply.^[58] Oxbow lakes originate from the cutoff of a meander loop when neck narrowing during high-flow events allows the river to breach the bend, abandoning the curved segment and forming a crescent-shaped, isolated water body. These lakes gradually fill with fine sediments from overbank flooding and organic matter, eventually becoming meander scars or dry depressions. The formation highlights the depositional phase following intense erosion, with oxbow lakes serving as sediment traps in floodplain environments.^[59] Examples include those along the Brazos River in Texas, where groundwater maintains water levels in active oxbows before siltation dominates.^[60] Alluvial fans are cone- or fan-shaped depositional landforms that accumulate at the base of mountain fronts or canyon mouths, where a sediment-laden stream suddenly debouches onto a broader, lower-gradient plain, causing rapid deceleration and sediment aggradation. Composed of unconsolidated gravels, sands, and silts sorted by decreasing grain size radially outward, these fans radiate from the apex in a convex-up profile. They form in arid to semi-arid settings with episodic high-discharge events, such as flash floods, building up over time through repeated avulsions and lobe progradation.^[61] Prominent examples occur in the Basin and Range Province of the western United States, where tectonic uplift enhances sediment supply from adjacent highlands.^[58] Waterfalls represent abrupt vertical drops in a stream profile, typically resulting from differential erosion where resistant caprock overlies softer underlying strata, leading to undercutting, plunge pool formation, and headward retreat. This creates a knickpoint that migrates upstream, steepening the channel gradient and accelerating incision in the upper reaches. Waterfalls are common in youthful river stages or areas of resistant lithology, influencing local base level and downstream sediment dynamics. Notable instances, like those on the Whitewater River in South Carolina, illustrate how alternating shale and limestone layers drive waterfall development through selective weathering and hydraulic scour.^[62]

Impact Landforms

Impact landforms are geological features primarily formed by the hypervelocity collisions of meteoroids, asteroids, or comets with planetary surfaces, resulting in distinctive structures shaped by shock waves, excavation, and gravitational modification.^[63] These landforms dominate the surfaces of airless bodies like the Moon and Mercury but are less preserved on Earth due to erosion and tectonic activity, with approximately 190 confirmed impact structures identified globally.^[63] The formation process involves an instantaneous event where kinetic energy is converted into heat and pressure, excavating material and producing diagnostic shock-metamorphic effects such as shatter cones and high-pressure minerals.^[64] The impact crater is the fundamental landform, characterized by a bowl-shaped depression surrounded by a raised rim, formed when the impacting body vaporizes upon contact and excavates a transient cavity that collapses.^[65] On Earth, simple impact craters—typically less than 4 km in diameter—exhibit a depth-to-diameter ratio of about 1:5 to 1:7, with a parabolic floor created by the outward and upward flow of target material during the excavation phase.^[63] A classic example is Meteor Crater in Arizona, a 1.2 km diameter simple crater formed approximately 50,000 years ago by an iron meteorite impact, preserving its sharp rim and interior breccia layers.^[63] The raised rim, elevated roughly 4% of the crater's diameter above the surrounding terrain, results from the accumulation of ejected debris and the inward slumping of wall material post-impact.^[64] In larger simple craters, a central peak may form due to the elastic rebound of the crater floor after excavation, uplifting fractured and shocked bedrock to expose deeper stratigraphic layers.^[64] This feature, often conical and 200–500 m high, is prominent in craters 2–15 km across and serves as a key identifier of impact origin, as seen in the 28 km diameter Mistastin Lake crater in Canada, where the central uplift reveals Proterozoic basement rocks altered by shock pressures exceeding 10 GPa.^[63] Unlike volcanic plugs, central peaks arise from instantaneous hypervelocity dynamics rather than prolonged magmatic ascent.^[64] Surrounding the crater, the ejecta blanket consists of layered, fragmented debris thrown out ballistically during the impact, forming a radial pattern that thins with distance according to an inverse cube law from the rim.^[64] This hummocky deposit, thickest near the rim (up to several times the crater depth), includes shocked target material and impactor fragments, extending 1–2 crater diameters outward and often displaying ray patterns on preserved surfaces like the Moon's Theophilus crater.^[63] On Earth, erosion typically obscures ejecta blankets, but remnants are evident around structures like the approximately 300 km Vredefort impact structure in South Africa, the largest verified impact feature, where they contribute to regional topographic highs.^[63] For craters exceeding 4 km in diameter on Earth (or about 15–20 km on the Moon), complex craters develop through gravitational instability, featuring collapsed, terraced walls, a flat floor, and multiple ring structures instead of a simple bowl.^[64] The transition to complexity occurs when the transient crater's walls exceed the local gravitational strength, leading to inward slumping that forms terraces and central uplifts or peak rings; depth-to-diameter ratios shallow to 1:10 or less.^[63] The Manicouagan Reservoir in Canada exemplifies a complex crater, with its 100 km annular structure formed 214 million years ago by an asteroid impact, now partially flooded but retaining a central island peak ring amid the collapsed rim.^[63] These features highlight the scale-dependent morphology of impact landforms, influenced by target properties and gravity.^[64]

Lacustrine Landforms

Lacustrine landforms are geomorphic features shaped by the depositional and erosional processes of standing water bodies, primarily lakes, where sedimentation occurs in relatively quiescent environments compared to flowing water systems. These landforms typically form through the accumulation of fine-grained sediments like silts, clays, and organic materials, often resulting in flat or depressed terrains that reflect past lake extents and water level fluctuations. Unlike fluvial landforms driven by stream currents, lacustrine features emphasize settling and evaporation in enclosed basins, contributing to soil formation and wetland development in post-glacial or arid regions.^[66] A lacustrine plain, also known as a lake plain, is a broad, flat expanse created when sediments progressively fill a lake basin, leading to the eventual drainage or evaporation of the water body and the emergence of level terrain. These plains are characterized by fine-grained, well-sorted deposits such as laminated clays and silts, often exhibiting varves—annual sediment layers from seasonal deposition—that indicate past lake dynamics. Lacustrine plains commonly develop in glaciated areas where meltwater lakes infill depressions, forming fertile agricultural lands but also prone to poor drainage due to the impermeable clay layers. For example, the extensive lacustrine plains in the Great Lakes region resulted from Pleistocene glacial lake sediments, covering thousands of square kilometers with uniform, low-relief surfaces.^[67][68] Salt pans, or evaporite flats, are crusted, barren surfaces formed in the desiccated beds of shallow, endorheic lakes in arid climates where evaporation exceeds inflow, concentrating dissolved minerals into a hard salt layer. These landforms develop in closed basins, starting as saline lakes that dry out periodically, leaving behind polygonal cracks and efflorescent crusts of halite, gypsum, and other evaporites up to several centimeters thick. The process involves sequential precipitation of minerals from supersaturated brines, with less soluble compounds like carbonates forming first at the margins and highly soluble salts like sodium chloride in the center. Prominent examples include the Bonneville Salt Flats in Utah, where ancient Lake Bonneville's evaporation produced vast, mirror-like expanses used for land speed records, highlighting their extreme flatness and durability under dry conditions. Salt pans influence local hydrology by acting as impermeable barriers and can expand through deflation, eroding surrounding sediments.^[69][70] Proglacial lakes are transient water bodies impounded by glacial ice, moraines, or ice-dammed terrain at the front of a retreating glacier, fed by meltwater and often filling erosional basins or topographic lows. These lakes form rapidly during deglaciation, with water trapped behind end moraines or against the glacier snout, leading to sediment deposition of varved silts and clays that record annual melt cycles. They are typically short-lived, draining catastrophically through outburst floods (jökulhlaups) when dams breach, but their sediments preserve evidence of glacial retreat rates and climate variability. In the Quaternary record, proglacial lakes like those in front of the Laurentide Ice Sheet provided paleoenvironmental data through layered deposits, with examples such as Glacial Lake Agassiz in North America spanning over 300,000 square kilometers at its peak. These features contrast with permanent lakes by their direct linkage to active glacial processes.^[71] Carolina bays are enigmatic, shallow elliptical depressions scattered across the Atlantic Coastal Plain, oriented northwest-southeast and ranging from tens of meters to several kilometers in length, often rimmed by sandy berms and containing wetlands or ponds. These landforms likely originated in lacustrine settings during the late Pleistocene, where shallow lakes or ponds were sculpted by prevailing southwesterly winds that drove rotational currents, eroding the southwest and northwest margins while depositing sand on the northeast and southeast sides to form the characteristic rims. Alternative mechanisms include thermokarst-like subsidence in organic-rich sediments, exacerbated by post-glacial warming and permafrost thaw, leading to irregular basins that pond water atop impermeable humate layers. Over 500,000 such bays exist from New Jersey to Florida, with radiocarbon dates on sediments indicating formation between 7,500 and 20,000 years ago; they support unique ecosystems like cypress swamps and are vital for biodiversity in otherwise flat coastal terrains.^[72]

Mountain and Glacial Landforms

Mountain and glacial landforms arise primarily from the erosional and depositional actions of glaciers in mountainous environments, shaping distinctive features through the movement of ice masses over bedrock and sediment. These landforms result from processes such as abrasion, plucking, and till deposition during glacial advances and retreats, often in alpine settings where valley glaciers dominate. Unlike fluvial or tectonic features, glacial landforms reflect the immense erosive power of ice, creating bold, sculpted topography that persists long after ice melt.^[73] Erosional landforms, such as cirques and U-shaped valleys, form where glaciers scour and widen pre-existing topography, while depositional features like moraines and drumlins emerge from the accumulation and reshaping of glacial debris. These structures provide key evidence for reconstructing past ice dynamics and climate conditions, with examples abundant in regions like the North American Rockies and European Alps. Glacial activity contrasts with periglacial processes by involving active ice flow rather than frozen ground alone.^[74][75] Cirque
A cirque is a bowl-shaped, amphitheater-like depression carved into the head or side of a mountain by glacial erosion, featuring steep walls and a lip at its lower edge. It forms through a combination of plucking, where ice freezes to and pulls away bedrock, and abrasion by rock fragments embedded in the glacier base, often initiating at high elevations where snow accumulates into ice. Post-glaciation, cirques may hold tarns, small lakes in the basin. Examples include those in the North Cascades National Park, Washington, illustrating cirque development in alpine glaciers.^[74][73][75] U-shaped valley
A U-shaped valley is a steep-sided, flat-bottomed trough with a parabolic cross-section, resulting from glacial erosion that transforms narrower, V-shaped stream valleys into broader channels. Glaciers widen the valley sides through lateral abrasion and deepen the floor via basal scouring, over-steepening walls in the process. This contrasts with the tapered profiles of river-eroded valleys. Prominent examples occur in Little Cottonwood Canyon, Utah, where glacial action during the Pleistocene left clear U-profiles.^[74][73][75] Moraine
A moraine consists of ridges or mounds of unstratified glacial till—unsorted debris ranging from clay to boulders—deposited directly by glacier ice at its margins or terminus. Formation occurs as the ice melts or advances, dropping entrained sediment; types include lateral moraines along valley sides, terminal moraines marking maximum extent, and medial moraines from merging glaciers. These features indicate former ice positions and flow paths. The terminal moraines on Long Island, New York, exemplify deposition from the Laurentide Ice Sheet's retreat.^[74][73][75] Drumlin
A drumlin is a streamlined, elongated hill of glacial till, typically 0.25 miles or longer, shaped by overriding ice into a teardrop form with a steeper, broader upstream end and a tapered, gentler downstream slope. It forms when glacier flow compresses and molds subglacial sediment, aligning it with ice direction; drumlins often cluster in fields numbering in the thousands. They reveal past glacial movement, as the long axis points down-ice. Notable examples include Spectacle and Long Islands in Boston Harbor, Massachusetts, formed during the last Ice Age.^[74][76][73]

Slope Landforms

Slope landforms encompass features shaped primarily by gravitational processes, including mass wasting and slow downslope movements that alter the stability and morphology of hillsides and escarpments. These landforms arise from the interplay of gravity, weathering, and soil or rock instability, often resulting in accumulations or rearrangements of material on inclined surfaces. Unlike erosional landforms driven by water or wind, slope landforms emphasize the downslope redistribution due to gravitational forces, contributing to landscape evolution in diverse settings from temperate hills to periglacial environments.^[5] Talus, also known as scree, consists of a sloping accumulation of loose, angular rock debris that forms at the base of a steep cliff or slope, primarily through repeated rockfalls where fragments detach and tumble downslope. This debris typically ranges from pebble to boulder size and creates a cone-shaped or apron-like deposit with angles of repose between 30° and 40°, stabilizing as individual clasts lock together under gravity. Formation occurs in environments with jointed bedrock susceptible to freeze-thaw cycles or seismic activity, leading to progressive buildup that can bury underlying terrain. Examples include talus slopes in arid mountain ranges, where minimal vegetation allows debris to remain unconsolidated.^[77][78] Escarpments are prominent, steep slopes or cliffs that demarcate abrupt changes in elevation between two relatively flat or gently undulating surfaces, often extending linearly for kilometers. They develop through differential erosion, where resistant rock layers cap softer underlying strata, causing the overlying material to erode more slowly and form a precipitous face, or via faulting that exposes inclined bedrock planes. The slope face can reach heights of tens to hundreds of meters, with the upper surface forming a plateau or dip slope that gently inclines away from the scarp. Notable instances include the Niagara Escarpment, a 725-kilometer feature resulting from erosion of resistant Silurian dolomites overlying weaker shales.^[79][80][81] Terracettes appear as small, parallel, step-like ridges or benches on grassy hillslopes, typically with treads 0.5 to 1 meter wide and risers 0.1 to 0.5 meters high, spaced 1 to 5 meters apart across slopes of 10° to 30°. These features form through soil creep, a gradual downslope movement of soil particles at rates of millimeters to centimeters per year, driven by gravity, wetting-drying cycles, and bioturbation from grazing animals that align their paths along the steps, accelerating the process. In periglacial or temperate pastures, terracettes create a staircase profile that traps water and soil, influencing local hydrology and vegetation patterns, as seen in the Loess Hills of Iowa.^[82][83][84] Solifluction sheets are broad, sheet-like deposits of saturated, unsorted soil and regolith that slowly flow downslope on gentle to moderate slopes in permafrost regions, typically at rates of 1 to 10 centimeters per year. This mass movement occurs when the active layer above permafrost thaws in summer, saturating the soil and reducing its shear strength, allowing gravity to drive laminar flow over the frozen substrate. Resulting landforms are smooth or slightly lobate sheets up to several meters thick and tens to hundreds of meters wide, often veneering valley sides in arctic and alpine tundra, such as those in the Canadian Arctic Archipelago. These features contrast with faster mass wasting by their viscous, non-channelized nature and role in periglacial landscape modification.^[85][5][6]

Tectonic Landforms

Tectonic landforms result from the deformation of the Earth's lithosphere due to internal forces associated with plate tectonics, including compression, extension, and shear that lead to folding and faulting of crustal rocks. These processes occur primarily at plate boundaries where lithospheric plates converge, diverge, or slide past one another, causing uplift, subsidence, and lateral displacement over geological timescales. Folding involves the bending of rock layers into arches and troughs under compressional stress, while faulting produces fractures along which rocks move relative to each other, often resulting in block displacements. Such deformations shape major landscape features, influencing topography and influencing subsequent erosion patterns, though the primary forms are structural rather than erosional.^[86] A horst is an uplifted block of the Earth's crust bounded by two parallel normal faults that dip away from it, formed during extensional tectonics where the central block remains elevated relative to the surrounding down-dropped areas. This structure typically arises in rift zones where the lithosphere is stretched, creating a series of alternating ridges and valleys; for example, the Vosges Mountains in France represent a prominent horst formed during the Oligocene rifting that also produced the adjacent Rhine Graben. Horsts contribute to the blocky terrain seen in regions like the Basin and Range Province of the western United States, where repeated extension has segmented the crust into numerous such uplifted blocks.^[87][88] In contrast, a graben forms as a down-dropped block between two parallel normal faults that dip toward it, resulting from crustal extension that thins and subsides the intervening section, often creating elongated rift valleys. These features are key indicators of divergent plate boundaries or intraplate rifts, with the subsidence accommodating the stretching of the lithosphere; the Rhine Valley in Germany exemplifies a graben, measuring about 300 kilometers long and up to 40 kilometers wide, developed from Cenozoic extension. Grabens can host sedimentary basins that accumulate deposits over time, as seen in the East African Rift system, where ongoing extension has produced deep valleys like the Great Rift Valley.^[87][88] A fault scarp is a steep, linear slope or cliff created by the vertical displacement along a fault plane that offsets the ground surface, typically visible immediately after seismic activity but gradually modified over time. These scarps form at the intersection of the fault with the Earth's surface during earthquakes or aseismic creep, with heights ranging from meters to tens of meters depending on the displacement magnitude; the Wasatch Fault in Utah features prominent fault scarps up to 5 meters high from recent Holocene displacements. Fault scarps serve as direct evidence of active tectonism, allowing geologists to date fault activity through scarp degradation studies.^[88][89] A dome refers to an uplifted, roughly circular or elliptical structure in the crust where rock layers arch upward and plunge outward in all directions, often resulting from compressional folding or the buoyant rise of underlying igneous intrusions that deform overlying strata. In tectonic contexts, domes form through interference folding or diapiric uplift, exposing older rocks at the core after erosion; the Black Hills of South Dakota illustrate a structural dome, uplifted during the Laramide Orogeny around 60 million years ago via compressional forces that arched Precambrian basement rocks. These features contrast with volcanic domes by emphasizing broad crustal deformation rather than extrusive magmatism, though some may involve minor igneous contributions without surface volcanism.^[90][91]

Volcanic Landforms

Volcanic landforms are geomorphic features resulting from the eruption of magma onto the Earth's surface, where molten rock, gases, and pyroclastic materials accumulate to form distinctive structures. These landforms arise primarily from effusive or explosive volcanic activity, often in tectonic settings such as hotspots or subduction zones, and include both constructive edifices and depressions.^[92] Unlike tectonic landforms driven by plate deformation, volcanic ones emphasize surface extrusions of magma.^[93] Shield volcanoes are broad, gently sloping volcanic edifices built almost entirely from successive layers of fluid basaltic lava flows that spread widely before cooling. The low viscosity of the lava allows it to travel great distances—often tens of kilometers—from the central vent, resulting in a dome-shaped profile with slopes typically less than 5 degrees.^[93] Mauna Loa in Hawaii exemplifies this type, standing over 4,000 meters above sea level with a base circumference exceeding 200 kilometers due to its voluminous eruptions. These volcanoes form primarily over mantle hotspots, where magma ascends with minimal interaction with crustal rocks.^[94] A caldera is a large, basin-shaped volcanic depression formed by the collapse of a volcano's summit following the evacuation of a shallow magma chamber during a major eruption. These features are typically 1 to 100 kilometers in diameter, far larger than typical craters, and result from the removal of supportive magma, causing the overlying rock to subside.^[95] The Yellowstone Caldera, for instance, measures about 45 by 85 kilometers and formed from multiple supereruptions over 2 million years ago, each ejecting more than 1,000 cubic kilometers of material.^[96] Calderas often fill with water to form lakes, as seen in Crater Lake, Oregon, and may exhibit resurgence through post-collapse uplift.^[97] Lava tubes are natural subterranean conduits that channel molten lava beneath the surface of a flow, formed when the outer layer of a pahoehoe lava flow cools and solidifies while the interior remains fluid. These tubes can extend for several kilometers and reach diameters of up to 30 meters, insulating the flowing lava and enabling efficient transport to distant flow fronts.^[98] In Hawaiian volcanoes like Kīlauea, extensive tube systems have facilitated eruptions over decades, with examples such as the Thurston Lava Tube preserving detailed records of past flows.^[99] Collapse of the tube roof after drainage often creates linear depressions or skylights, aiding in the study of volcanic plumbing.^[100] Cinder cones, also known as scoria cones, are steep-sided, symmetrical hills constructed from the accumulation of pyroclastic fragments ejected during moderately explosive eruptions of basaltic to andesitic magma. These fragments, including cinders and bombs, pile around a single vent, forming cones with slopes of 25 to 40 degrees and heights rarely exceeding 400 meters.^[101] Parícutin in Mexico, which grew 424 meters in a year starting in 1943, illustrates rapid formation through repeated Strombolian eruptions.^[93] These landforms are short-lived geologically, often eroding quickly, and commonly occur in volcanic fields alongside other cone types.^[102]

Weathering Landforms

Weathering landforms arise from the in-place disintegration of bedrock through physical, chemical, and biological processes, without significant material transport, distinguishing them from erosional or depositional features. These processes weaken rock structures at or near the Earth's surface via interactions with atmospheric, hydrological, and biotic agents, often leading to distinctive surface morphologies in various climates. Physical weathering involves mechanical breakdown, such as through thermal expansion or crystal growth, while chemical weathering alters mineral compositions via hydrolysis, oxidation, or dissolution; biological activity, like root wedging or microbial acids, can enhance both. In arid and semi-arid environments, salt crystallization emerges as a dominant mechanism, exploiting rock porosity to create cavernous features, whereas in humid settings, subsurface moisture may preferentially etch basal zones.^{[103][104][78]} Such landforms typically develop on exposed rock outcrops, inselbergs, or cliff faces, where differential weathering rates—driven by rock heterogeneity, jointing, or microclimatic variations—produce isolated or patterned hollows, protrusions, or concavities. For instance, in coastal or desert regions, saline solutions infiltrate pores, and upon evaporation, expanding salt crystals pry apart mineral grains, enlarging voids over time. This preparatory breakdown often sets the stage for subsequent erosion, but the features themselves remain as weathering signatures. Examples abound in granitic or sedimentary terrains worldwide, from the Mojave Desert to Australian outback, highlighting weathering's role in landscape evolution under stable tectonic conditions.^[105][106] Tafoni represent cavernous weathering hollows that form rounded, bowl-shaped cavities on rock faces, typically ranging from centimeters to meters in depth and width, often with overhanging lips and nested smaller pits inside. These features develop primarily through salt crystallization in porous rocks like sandstone, granite, or rhyolite tuff, where seawater or groundwater introduces salts that precipitate during evaporation, exerting expansive pressures up to 100-200 MPa to dislodge grains. Common in arid deserts and coastal zones, tafoni create a lace-like or swiss-cheese texture, as seen in the Navajo Sandstone of Arches National Park or the rhyolite at The Honeycombs in Utah, where wind enhances salt accumulation by promoting rapid drying. The process can initiate in under a century on susceptible substrates, with microorganisms sometimes stabilizing thin walls to preserve the form.^{[105][107][92][106]} Tors are isolated, steep-sided rock masses or knobs protruding above surrounding pediments, formed by differential weathering that exploits pre-existing joints or fractures in bedrock, leaving more resistant corestones elevated. In arid and semi-arid settings, such as the Mojave Desert's Cima Dome or Scotland's Cairngorm Mountains, subsurface chemical weathering along joint planes dissolves minerals like feldspar, creating a two-stage process: initial deep regolith formation followed by episodic stripping via climate shifts or fluvial incision to exhume the tors. Joint spacing greater than 1-2 meters and higher biotite content in granites promote slower weathering in pod interiors, yielding tors up to 10-20 meters high with angular piedmont junctions. Unlike structural control alone, sediment-blanket dynamics amplify exposure, as thinning regolith triggers bedrock incision rates exceeding 0.01 mm/year in stable landscapes.^{[108][109][110]} Flared slopes manifest as smooth, basal concavities at the foot of rock outcrops or inselbergs, typically 1-5 meters deep and spanning 10-50 meters wide, resulting from groundwater sapping that undercuts steeper upper faces. This two-stage etching occurs via subsurface moisture migration along permeable zones, dissolving soluble minerals like quartz or feldspar at the scarp-piedmont interface, often in granitic terrains of arid Australia or the southwestern U.S. Sapping involves concentrated seepage emerging at the base, eroding alcoves that cause overlying rock to spall and retreat, forming the concave profile without widespread surface runoff. Rates may reach 0.1-1 mm/year in humid microenvironments, contrasting with slower upper-slope weathering, and are evident in features like those around Uluru, where flared bases transition to planar pediments.^{[111][112][113]} Honeycomb weathering produces interconnected networks of small pits or alveoli, 1-10 cm across, on exposed rock surfaces, resembling a beehive pattern and arising from combined wind abrasion and salt crystallization in arid environments. In rocks like limestone or sandstone, wind directs saline moisture into pores, where evaporation fosters crystal growth that flakes off granular layers, deepening pits while case-hardening protects ridges between them. This differential process thrives in hyper-arid coasts or deserts, such as Capitol Reef National Park's Entrada Sandstone or Puget Sound's shorelines, where salt residues visibly coat the features. Development accelerates under fluctuating humidity, with pit enlargement rates up to 0.5 mm/year, often merging into larger tafoni over millennia.^{[78][107][114][115]}

Landforms by Shape

Positive Landforms

Positive landforms are elevated topographic features that rise above the surrounding terrain, creating positive relief through processes such as tectonic uplift, differential erosion, and weathering resistance.^[116] These landforms are distinguished by their prominence and are categorized based on shape, size, and formation mechanisms, often serving as key indicators of underlying geological structures and surface processes in geomorphology.^[5] Unlike flat expanses or lowered basins, positive landforms exhibit varying degrees of steepness and isolation, influencing local hydrology, ecology, and human settlement patterns. Hills represent one of the most common positive landforms, defined as relatively small elevations that rise above adjacent areas, typically with gentle slopes and rounded profiles.^[117] They often lack the sharp peaks of mountains and are formed through erosional sculpting of uplifted terrain or accumulation of resistant materials, with relief generally under 600 meters in many classificatory systems, though no universal height threshold exists.^[118] Examples include the rolling hills of the Appalachian region, where sedimentary and metamorphic rocks have been shaped by prolonged fluvial and glacial action over millions of years.^[4] Buttes are isolated, steep-sided hills with flat tops, emerging as erosional remnants where a resistant caprock layer protects underlying softer sediments from weathering.^[119] The caprock, often composed of sandstone or lava flows, forms a protective overhang that slows vertical erosion, resulting in vertical cliffs and a table-like summit typically spanning less than a few kilometers in area.^[120] Prominent buttes, such as those in Monument Valley, Utah, illustrate how differential erosion in arid environments isolates these features from broader plateaus over geological timescales.^[55] Domes constitute smooth, rounded positive landforms characterized by a broad, arch-like uplift without distinct peaks, where rock layers dip gently outward from a central high point.^[121] They arise from structural deformation, such as salt or igneous intrusions piercing overlying strata, or from erosional processes that bevel uplifted blocks into curved profiles.^[122] The Black Hills of South Dakota exemplify a large-scale dome, formed by Precambrian uplift and subsequent erosion that exposed resistant core rocks in a symmetric, rounded form rising approximately 1,200 meters above the surrounding plains.^[123] Inselbergs are abrupt, isolated hills or monoliths that protrude sharply from flat plains, often composed of weathered-resistant granite or gneiss that stands as a relic of ancient landscapes.^[124] These features form through deep chemical weathering and parallel slope retreat, leaving residual hills amid pedimented surroundings after surrounding softer materials erode away.^[125] Uluru (Ayers Rock) in Australia serves as a classic inselberg, a massive sandstone dome-like outcrop exceeding 300 meters in height, shaped by millions of years of arid erosion on a once-extensive erosion surface.^[126]

Depressions

Depressions encompass a variety of sunken or hollow landforms that occur below the level of surrounding terrain, typically resulting from processes like subsidence, dissolution, glacial melting, or tectonic settling. These features often exhibit internal drainage patterns, where water collects within the depression rather than flowing outward, and they play significant roles in local hydrology and geomorphology. Unlike elevated or flat terrains, depressions represent negative relief, facilitating the accumulation of sediments, water, or even forming natural enclosures for ecosystems. A basin is a broad, low-lying topographic depression characterized by internal drainage, where surface water converges and is contained within the feature rather than draining to external systems. Geologically, basins often form as large-scale sedimentary structures, representing volumes of rock strata deposited in subsiding areas bounded by structural highs, such as the Appalachian Basin, an elongate depression filled with Paleozoic sedimentary rocks up to 12,000 meters thick in places. These landforms can span hundreds of kilometers and influence regional groundwater flow and petroleum reservoirs due to their enclosed nature. Kettles, also known as kettle holes, are shallow, bowl-shaped depressions typically found in glacial outwash plains or moraines, formed by the melting of isolated blocks of glacier ice buried under sediment. As the ice block melts, the overlying glacial deposits collapse into the void, creating a steep-sided hollow that may fill with water to form a kettle lake; examples abound in post-glacial landscapes like those in the northern United States, where kettles range from a few meters to over 10 kilometers in diameter. This process highlights the role of glacial retreat in sculpting irregular terrain. A sinkhole, or doline, is a closed surface depression resulting from the subsurface dissolution of soluble rocks like limestone or from the collapse of overlying material into an underground cavity. In karst regions, sinkholes develop gradually through chemical weathering, where rainwater acidified by carbon dioxide erodes bedrock, leading to surface subsidence; they vary in size from small pits to large craters exceeding 100 meters in depth, as seen in Florida's karst terrain. While often associated with karst landscapes, sinkholes can also form in other settings like evaporite deposits through similar collapse mechanisms. A cenote is a distinctive type of sinkhole characterized as a natural well formed by the collapse of a limestone cave roof, exposing groundwater below and creating a steep-walled pit often filled with clear water. Predominantly found in the Yucatán Peninsula of Mexico, cenotes result from the dissolution of permeable limestone in tropical karst environments, where fractures allow water to carve extensive underground networks before roof failure occurs; the Great Cenote of Chichén Itzá, for instance, reaches depths of about 20 meters and served as a vital water source for ancient Maya civilizations.

Flat Landforms

Flat landforms are characterized by low relief and minimal slopes, typically resulting from depositional processes or extensive erosion that levels the terrain over broad areas. These features contrast with more rugged or elevated landforms by emphasizing horizontal expanses that facilitate agriculture, settlement, and water flow. They often form in response to sedimentary accumulation or long-term denudation, creating stable surfaces with gentle gradients.^[127] A plain is a broad expanse of flat or gently undulating land with minimal elevation changes, often lacking prominent hills or valleys. These landforms cover significant portions of Earth's surface and are primarily depositional in origin, formed by the accumulation of sediments from rivers, winds, or waves over time. For instance, the Great Plains of North America exemplify how glacial outwash and fluvial deposits can create vast, fertile lowlands suitable for farming. Plains may also arise from erosional planation, where prolonged weathering reduces highlands to near-level surfaces, though depositional mechanisms dominate in many cases.^[127][128] Plateaus represent elevated flatlands bounded by steep escarpments or cliffs, distinguishing them from surrounding lower terrain through their raised position and horizontal summit. They form through tectonic uplift of sedimentary layers or accumulation of lava flows, followed by limited erosion that preserves the flat top while dissecting the edges. The Colorado Plateau illustrates this, where ancient seabeds were uplifted and incised by rivers, maintaining a high, even surface over millions of years. Unlike broader plains, plateaus exhibit greater vertical relief at their margins, often exceeding hundreds of meters, and support unique ecosystems adapted to their isolation.^[127][129] Floodplains consist of flat, sediment-rich areas adjacent to rivers, periodically inundated during floods to build up layers of alluvium. These landforms develop through repeated deposition of fine-grained materials like silt and clay when river velocities decrease during overflow, creating fertile soils that enhance biodiversity and agriculture. The Mississippi River floodplain demonstrates this process, where seasonal flooding has deposited thick sediment layers, forming natural levees and backswamps over millennia. Floodplains play a critical role in flood mitigation by storing water and nutrients, though human alterations like dams can reduce sediment supply and lead to erosion.^[130][131] A pediplain is a vast, nearly flat erosional surface in arid or semi-arid regions, produced by the coalescence of multiple pediments—gently sloping aprons at the base of retreating scarps. This landform emerges from prolonged parallel slope retreat under sparse vegetation and infrequent but intense rainfall, where mechanical weathering and sheetwash erode mountain fronts without deep incision. Examples include the extensive pediplains of southern Africa, as described in L.C. King's theory, where billion-year-old cratons have been reduced to low-relief plains through sustained denudation rates of about 10-30 meters per million years. Pediplains differ from humid peneplains by lacking dense fluvial networks, relying instead on episodic gullying and pediment expansion.^[132][133]

Additional Landform Categories

Karst Landforms

Karst landforms arise from the chemical dissolution of soluble bedrock, such as limestone, dolomite, and evaporites, primarily by slightly acidic groundwater and surface water in regions of high permeability. This process, termed karstification, sculpts terrain through subsurface erosion, leading to distinctive surface features like closed depressions and underground drainage networks, while creating highly vulnerable aquifers.^[134] Karst landscapes are most developed in humid climates where carbonic acid from rainwater and soil enhances rock solubility, resulting in irregular topography that contrasts with mechanical erosion-dominated areas.^[135] These landforms are globally significant for their role in groundwater storage and as habitats, though they pose engineering challenges due to subsidence risks.^[136] A key karst feature is the polje, a large, flat-floored closed depression formed by subsidence in karst basins, often spanning several kilometers in length and width. These depressions typically have floors of bare limestone or alluvium deposits, bounded by steep surrounding walls, and develop where tectonic or dissolution processes cause gradual sinking of the surface.^[134] Poljes often serve as seasonal wetlands or agricultural plains, with examples in the Dinaric Karst of Croatia and Bosnia, where alluvial infilling creates fertile flatlands amid rugged terrain.^[137] The uvala represents a compound sinkhole resulting from the coalescence of multiple smaller dolines (individual sinkholes), forming a larger closed depression with an uneven floor. This landform emerges as adjacent sinkholes enlarge and merge through progressive dissolution, typically measuring tens to hundreds of meters across and exhibiting elongate or irregular shapes.^[134] Uvalas are transitional in scale between simple dolines and larger poljes, commonly observed in mature karst regions like the Carpathian Mountains, where they facilitate subsurface drainage.^[138] Cockpit karst describes a tropical karst landscape dominated by numerous rounded, closed depressions (cockpits) interspersed with conical residual hills, creating a pitted, egg carton-like topography. These features form under intense humid conditions that promote uniform dissolution of thick limestone, with each depression draining via sink points to underlying aquifers.^[134] The landform is exemplified in Jamaica's interior highlands, where densities of depressions can exceed 20 per square kilometer, and similar patterns occur in China's Guangxi region.^[137] In contrast, tower karst features isolated, steep-sided residual hills or towers rising abruptly from flat alluvial plains, shaped by differential dissolution that spares more resistant rock pinnacles while eroding surrounding areas. These towers, often flat-topped and forested, can reach heights of 100 meters or more and are separated by sediment-filled lowlands.^[134] Tower karst evolves in subtropical to tropical settings with high rainfall, as seen in Vietnam's Ha Long Bay and southern China's Guilin area, where tectonic stability enhances long-term development.^[138]

Anthropogenic Landforms

Anthropogenic landforms are features of the Earth's surface deliberately shaped or constructed by human activities, fundamentally altering natural geomorphic processes such as erosion, sediment transport, and hydrology. These landforms emerge from agriculture, mining, waste management, and water engineering, often persisting for centuries and influencing ecological and social systems. Unlike natural formations, they reflect intentional modifications to support resource extraction, food production, or infrastructure, with global examples spanning ancient terraces to modern excavations. Their study integrates geomorphology with human geography, highlighting how such features can both stabilize and destabilize landscapes over time. Agricultural terraces represent one of the most widespread anthropogenic landforms, constructed on slopes to mitigate soil erosion and facilitate cultivation in hilly terrains. These stepped fields are built using stone walls, earth embankments, or cut-and-fill methods, creating level platforms that intercept downslope water and sediment flow. Originating over 8,000 years ago, they enhance soil depth, moisture retention, and fertility, enabling higher population densities in regions like the European Alps and Mediterranean. For instance, in Italy's Cinque Terre, terraces have modified landscapes for about 1,000 years, reducing erosion rates but requiring ongoing maintenance to prevent wall collapse and sediment buildup. Abandonment of these systems can lead to accelerated degradation, underscoring their role in long-term landscape resilience. Strip mine pits, also known as open-pit mines, are vast excavations formed by surface mining techniques that remove overburden to access shallow mineral deposits, creating pronounced depressions in the terrain. These landforms feature stair-step benches to stabilize steep walls and prevent landslides, with depths reaching up to 1.2 km, as seen in Utah's Bingham Canyon Mine, one of the world's largest at 7.7 km² in area. Mining disrupts natural erosion by stripping vegetation, blasting rock, and generating massive waste rock volumes—often 98% or more of extracted material—leading to altered hydrology, lowered water tables, and increased slope instability. In Appalachia, mountaintop removal mining flattens ridges and fills valleys, producing persistent low-relief pits that store water and sediment, reducing landscape connectivity and sustaining high erosion rates through pyrite oxidation. Such pits exemplify humanity's tangible impact on geomorphic systems, with reclamation efforts aiming to restore but often failing to mimic natural forms. Landfill mounds are artificial hills constructed from layered waste materials capped with soil, forming constructional landforms that rise prominently above surrounding topography. Engineered with maximum slopes of 3:1 for stability, these mounds can reach heights of 225 feet, as in New York City's Fresh Kills Landfill, which covers half of a 2,200-acre site. They consist of human-transported materials (HTM) like garbage and artifacts, classified under anthropogenic soils such as the artifactic family (>35% persistent artifacts in a >50 cm layer). Compaction causes settling to 80-85% of original height within five years, while thin, low-quality cover soils limit vegetation and expose surfaces to erosion and gas seepage. Visually stark against natural landscapes, these mounds alter local hydrology and create root-limiting layers, persisting as markers of waste disposal practices. Artificial canals are engineered waterways dug to redirect flow, transport goods, or irrigate land, profoundly modifying fluvial landforms by simplifying channels and disconnecting floodplains. Constructed by excavating linear paths, they increase water velocity and drainage efficiency but reduce natural dynamism, as evidenced by the lower Mississippi River where ~3,000 km of levees and cutoffs shortened the channel by 235 km and lowered bed elevations by 0.5-5 m. This engineering has decreased sediment delivery by over 60%—from 400 million metric tons annually—accelerating subsidence and wetland loss in deltas through saltwater intrusion. Canals also create new depositional patterns and habitat diversity along banks, though they often exacerbate erosion downstream and fragment ecosystems, as in Louisiana's coastal modifications where they contribute to ~4,900 km² of land loss since the early 20th century.

Alphabetical Glossary

A to M

A

• Abyssal plain: A flat or very gently sloping area of the deep ocean basin floor, located at depths exceeding 10,000 feet and covering approximately 70% of the ocean floor. See Flat Landforms.^[30]
• Abime: A vertical shaft in karstic limestone areas, formed by dissolution processes. See Karst Landforms.^[7]
• Alluvial fan: A cone-shaped depositional landform formed where a stream emerges from a steep valley onto a plain, with axial lengths ranging from tens of meters to tens of kilometers and radiating slopes from an apex. See Positive Landforms.^[7]
• Amphitheatre: A curved valley head of non-glacial origin, often developed in arid or humid climates through headward erosion in gently inclined sedimentary rocks or volcanic domes. See Depressions.^[7]
• Arête: A steep-sided, fretted ridge separating valley or cirque glaciers, resulting from glacial undercutting of rock slopes, commonly found where peaks rise above ice as nunataks. See Positive Landforms.^[7]
• Arroyo: A steep-sided, flat-bottomed ephemeral stream channel in arid regions, characterized by intermittent flow. See Weathering Landforms.^[7]
• Atoll: A ring-shaped coral reef structure, ranging from less than 1 km to over 100 km in diameter, enclosing a lagoon 30-100 m deep, with steep seaward slopes to the ocean floor. See Depressions.^[7]

B

• Badlands: Deeply dissected erosional landscapes in soft rock terrain, typically in semi-arid regions, dominated by overland-flow erosion with high drainage density of rills and gullies and sparse vegetation; the term derives from French "terres mauvaises" for difficult terrain. See Weathering Landforms.^[7]
• Bajada: A broad apron of coalesced alluvial fans forming a continuous piedmont between mountain fronts and basin floors, common in semi-arid basin-and-range terrain like the southwestern United States. See Flat Landforms.^[7]
• Bar: An elongated ridge or mound of sand or gravel, a few meters wide, deposited by waves and currents, submerged at high tide but possibly exposed at low tide, occurring off beaches, river mouths, or lagoon entrances. See Positive Landforms.^[7]
• Barrier island: A long, narrow island of sand parallel to the coast, separated from the mainland by a lagoon, formed by wave and current deposition. See Positive Landforms.^[7]
• Basin: A large depression in the Earth's surface, often with centripetal drainage, such as in basin-and-range terrain where fault blocks create down-dropped areas between uplifted ranges. See Depressions.^[7]
• Bay: A wide coastal re-entrant exceeding 1 km between headlands, with a seaward boundary broader than its landward penetration. See Depressions.^[7]
• Beach: A wave-deposited accumulation of sediment between modal wave base and the upper swash limit, gently sloping along coasts. See Flat Landforms.^[7]
• Beach ridge: Sub-parallel ridges of sand, gravel, or shell detritus in the foreshore zone, marking boundaries between low and high water on seas or lakes. See Positive Landforms.^[7]
• Blowout: A saucer-shaped hollow or trough in vegetated dunes, excavated by wind with an advancing spill of sand downwind. See Weathering Landforms.^[7]
• Bolson: A closed depression with centripetal drainage surrounded by hills, often featuring a central saline playa, typical of semi-arid basin-and-range areas. See Depressions.^[7]
• Bornhardt: A dome-shaped, steep-sided hill of massive igneous rock like granite, with bare convex slopes, little talus, and flattened summit, formed by differential weathering leaving resistant compartments. See Positive Landforms.^[7]
• Boulder field: An accumulation of large angular rock fragments, also known as blockfield or felsenmeer, often at slope bases from weathering. See Weathering Landforms.^[7]
• Braided river: A river with a wide, horizontal channel bed where low flows form interlacing sub-channels split and coalescing downstream over bars. See Positive Landforms.^[7]
• Butte: A small, steep-sided, flat-topped hill of soft rocks capped by resistant sedimentary layer, lava, or duricrust, smaller than a mesa and an advanced stage of its degradation. See Positive Landforms.^[7]

C

• Caldera: A large crater or depression from volcanic explosion or collapse of a volcano's central part, often several kilometers wide. See Volcanic Landforms.^[7]
• Canyon: A deeply incised, steep-sided river valley, often with vertical walls from rapid erosion. See Depressions.^[7]
• Cape: A prominent coastal protrusion where coastline meets mountains, hills, or plateaus, often at drainage divides, though some are low-lying like Cape Canaveral. See Positive Landforms.^[7]
• Cave: A natural underground hollow or passage, commonly formed by dissolution in karst or volcanic activity. See Karst Landforms.^[7]
• Cirque: A bowl-shaped depression with steep walls at the head of a glacial valley, carved by glacial erosion, also called corrie or cwm. See Depressions.^[7]
• Cliff: A rocky near-vertical slope, often exceeding 40° and sometimes overhanging. See Positive Landforms.^[7]
• Cliff, marine: A steep coastal slope in rock, produced by basal marine erosion undercutting, exposing formations. See Weathering Landforms.^[7]
• Cockpit karst: Hummocky terrain of conical residual hills surrounded by depressions, produced by limestone solution. See Karst Landforms.^[7]
• Col: A well-defined low point or pass between peaks or ridges, formed by glacial or fluvial erosion. See Depressions.^[7]
• Cone: A landform with a circular base and pointed summit, such as volcanic cones built by eruptions. See Volcanic Landforms.^[7]
• Cone karst: Karst landscape dominated by residual hills, known as fengcong in China. See Karst Landforms.^[7]
• Crag-and-tail: A glacial landform where hard rock (crag) protects softer lee rock, forming a tapered ridge (tail) from ice override. See Positive Landforms.^[7]
• Crater: A rounded depression at a volcano summit from eruption or by meteorite impact. See Volcanic Landforms.^[7]
• Cuesta: An asymmetric ridge with gentle dip slope and steep scarp, from differential erosion of dipping rock layers. See Positive Landforms.^[7]
• Cuspate foreland: A triangular depositional area of sand or shingle extending seaward with straight or concave shores, showing progradation via multiple beach ridges. See Positive Landforms.^[7]

D

• Delta: A depositional landform at a river mouth where sediment accumulates as flow slows into standing water, often triangular in shape. See Flat Landforms.^[7]
• Depression: A low-lying area below surrounding terrain, such as a basin or hollow formed by erosion or tectonics. See Depressions.^[7]
• Desert: An arid region with low precipitation, featuring landforms like dunes or playas from wind and water scarcity. See Weathering Landforms.^[7]
• Dome: A rounded, upward-convex landform from igneous intrusion or rock folding, often smooth-surfaced. See Positive Landforms.^[7]
• Drumlin: An elongated, streamlined hill of glacial till, shaped by ice movement with a steeper stoss end and gentler lee. See Positive Landforms.^[7]
• Dune: A mound or ridge of wind-blown sand in deserts or coastal areas, migrating via saltation and creep. See Positive Landforms.^[7]

E

• Escarpment: A steep slope or cliff separating level areas, often from faulting or differential erosion. See Positive Landforms.^[7]
• Estuary: A semi-enclosed coastal water body where river meets sea, mixing fresh and salt water with funnel-shaped mouth. See Depressions.^[7]

F

• Floodplain: A flat area adjacent to a river, built by sediment deposition during floods, subject to inundation. See Flat Landforms.^[7]
• Fjord: A long, narrow, deep sea inlet between high cliffs, carved by glacial erosion and later flooded. See Depressions.^[7]

G

• Gorge: A narrow, deep valley with steep sides, carved by rivers through resistant rock. See Depressions.^[7]
• Graben: A down-dropped block of land between faults from extensional tectonics, forming elongated valleys. See Depressions.^[7]
• Gully: A small, steep-sided channel eroded by concentrated runoff, larger than a rill but smaller than a valley. See Weathering Landforms.^[7]

H

• Headland: A coastal point of resistant rock jutting into the sea, resisting erosion relative to adjacent bays. See Positive Landforms.^[7]
• Hill: A natural elevation smaller than a mountain, with moderate relief and slopes. See Positive Landforms.^[7]
• Hogback: A narrow, sharp ridge from erosion of steeply dipping resistant rock layers. See Positive Landforms.^[7]
• Horn: A sharp, pyramid-shaped peak from glacial erosion of multiple surrounding cirques. See Positive Landforms.^[7]
• Hummock: A small, rounded mound or hill, often glacial or volcanic in origin. See Positive Landforms.^[7]

I

• Inselberg: An isolated hill or mountain rising abruptly from a plain, typically in arid regions from differential weathering. See Positive Landforms.^[7]
• Isthmus: A narrow land strip connecting two larger masses, separating bodies of water. See Positive Landforms.^[7]

K

• Karst: A landscape from dissolution of soluble rocks like limestone, featuring sinkholes, caves, and underground drainage. See Karst Landforms.^[7]
• Kettle: A depression from melting of buried glacial ice blocks, often holding water as kettle lakes. See Depressions.^[7]

L

• Lagoon: A shallow water body separated from the sea by a barrier like reef or spit. See Depressions.^[7]
• Lake: A standing body of water surrounded by land, formed in depressions by various processes. See Depressions.^[7]
• Levee: A natural embankment along a river from flood sediment deposition, raising channel banks. See Positive Landforms.^[7]
• Loess: Wind-deposited silt forming fertile plains, with thick deposits up to hundreds of meters in places like the Chinese Loess Plateau. See Flat Landforms.^[7]

M

• Massif: A compact group of mountains or highland block, often resistant to erosion. See Positive Landforms.^[7]
• Meander: A sinuous bend in a river channel from lateral erosion and deposition. See Weathering Landforms.^[7]
• Mesa: A flat-topped hill with steep sides from erosion of horizontal rock layers, larger than a butte. See Positive Landforms.^[7]
• Moraine: A ridge or mound of glacial debris like till, deposited by ice advance or retreat. See Positive Landforms.^[7]
• Mountain: A high land elevation with steep slopes and significant relief, typically over 600 m, formed by tectonics or volcanism. See Positive Landforms.^[7]

N

• Nunatak: See Glacial Landforms. An exposed peak or ridge of bedrock protruding through glacial ice, often serving as a refuge for plants and animals during ice ages.^[74]
• Natural arch: See Weathering Landforms. A rock formation created by erosion, where a bridge-like structure spans an opening, typically in arid or coastal environments.^[6]

O

• Outwash plain: See Glacial Landforms. A flat, broad area formed by meltwater depositing sediment beyond a glacier's terminus, often featuring braided streams.^[5]

P

• Pediment: See Weathering Landforms. A gently sloping, rocky surface at the base of a mountain, formed by erosion and deposition in arid regions.^[5]
• Peninsula: See Positive Landforms. A landform surrounded by water on three sides, extending from a larger landmass, such as the Arabian Peninsula.^[2]
• Pingo: See Cryogenic Landforms. A conical mound of soil-covered ice formed by groundwater freezing in permafrost regions; derived from the Inuit word pinguq meaning "little hill," with some reaching up to 70 meters high.^[51]
• Plain: See Flat Landforms. An extensive, flat or gently undulating area of low relief, often formed by sediment deposition, covering vast regions like the Great Plains.^[2]
• Plateau: See Positive Landforms. An elevated, flat-topped landform rising abruptly above surrounding areas, often dissected by rivers; examples include the Colorado Plateau, spanning hundreds of kilometers.^[139]
• Playa: See Flat Landforms. A flat-bottomed depression in a desert basin that temporarily fills with water after rains, forming a shallow lake that evaporates to leave salt flats.^[5]

Q

No common landforms begin with Q.

R

• Ridge: See Positive Landforms. An elongated, narrow elevation of land, often linear and formed by tectonic uplift or erosion, such as mid-ocean ridges.^[6]
• Reef: See Coastal Landforms. A ridge of rock, coral, or sand near the water's surface, acting as a barrier; coral reefs can extend for thousands of kilometers.^[2]

S

• Sand dune: See Aeolian Landforms. Mounds of sand shaped by wind, varying in size from small ripples to massive dunes over 300 meters high in deserts like the Sahara.^[21]
• Sea stack: See Coastal Landforms. An isolated column of rock remaining after wave erosion isolates it from a cliff, often featuring arches before separation.^[2]
• Sinkhole: See Karst Landforms. A depression formed by the collapse of surface material into an underground cavity dissolved in soluble bedrock like limestone.^[140]
• Strait: See Coastal Landforms. A narrow waterway connecting two larger bodies of water, bordered by land on both sides, such as the Strait of Gibraltar.^[2]

T

• Terrace: See Fluvial Landforms. A step-like, flat surface along a river valley, formed by erosion or deposition during changing base levels.^[5]
• Tombolo: See Coastal Landforms. A narrow strip of sand or gravel connecting an island to the mainland or another island, formed by longshore drift.^[141]

U

• U-shaped valley: See Glacial Landforms. A steep-sided, flat-bottomed valley carved by glacial erosion, contrasting with V-shaped fluvial valleys.^[6]

V

• Valley: See Depressions. A low area between hills or mountains, often carved by rivers or glaciers, ranging from narrow gorges to broad basins.^[2]
• Volcano: See Positive Landforms. A vent in Earth's crust through which molten rock erupts, building conical mountains; shield volcanoes can span over 100 kilometers wide.^[2]

W

• Wadi: See Fluvial Landforms. A dry riverbed or valley in desert regions that fills with water during rare flash floods.^[5]
• Waterfall: See Fluvial Landforms. A vertical drop in a river's course over a cliff, formed by differential erosion; Niagara Falls drops 57 meters.^[2]

X

No common landforms begin with X.

Y

• Yardang: See Aeolian Landforms. A streamlined, wind-eroded ridge in desert terrain, resembling an inverted boat hull, with lengths up to several kilometers.^[142]

Z

No common landforms begin with Z.