Hubbry Logo
GeomorphologyGeomorphologyMain
Open search
Geomorphology
Community hub
Geomorphology
logo
8 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Geomorphology
Geomorphology
Geomorphology
View on Wikipedia
from Wikipedia
Badlands incised into shale at the foot of the North Caineville Plateau, Utah, within the pass carved by the Fremont River and known as the Blue Gate. G. K. Gilbert studied the landscapes of this area in great detail, forming the observational foundation for many of his studies on geomorphology.[1]
Surface of Earth, showing higher elevations in red

Geomorphology (from Ancient Greek γῆ (gê) 'earth' μορφή (morphḗ) 'form' and λόγος (lógos) 'study')[2] is the scientific study of the origin and evolution of topographic and bathymetric features generated by physical, chemical or biological processes operating at or near Earth's surface. Geomorphologists seek to understand why landscapes look the way they do, to understand landform and terrain history and dynamics and to predict changes through a combination of field observations, physical experiments and numerical modeling. Geomorphologists work within disciplines such as physical geography, geology, geodesy, engineering geology, archaeology, climatology, and geotechnical engineering. This broad base of interests contributes to many research styles and interests within the field.

Overview

[edit]
Waves and water chemistry lead to structural failure in exposed rocks.

Earth's surface is modified by a combination of surface processes that shape landscapes, and geologic processes that cause tectonic uplift and subsidence, and shape the coastal geography. Surface processes comprise the action of water, wind, ice, wildfire, and life on the surface of the Earth, along with chemical reactions that form soils and alter material properties, the stability and rate of change of topography under the force of gravity, and other factors, such as (in the very recent past) human alteration of the landscape. Many of these factors are strongly mediated by climate. Geologic processes include the uplift of mountain ranges, the growth of volcanoes, isostatic changes in land surface elevation (sometimes in response to surface processes), and the formation of deep sedimentary basins where the surface of the Earth drops and is filled with material eroded from other parts of the landscape. The Earth's surface and its topography therefore are an intersection of climatic, hydrologic, and biologic action with geologic processes, or alternatively stated, the intersection of the Earth's lithosphere with its hydrosphere, atmosphere, and biosphere.

The broad-scale topographies of the Earth illustrate this intersection of surface and subsurface action. Mountain belts are uplifted due to geologic processes. Denudation of these high uplifted regions produces sediment that is transported and deposited elsewhere within the landscape or off the coast.[3] On progressively smaller scales, similar ideas apply, where individual landforms evolve in response to the balance of additive processes (uplift and deposition) and subtractive processes (subsidence and erosion). Often, these processes directly affect each other: ice sheets, water, and sediment are all loads that change topography through flexural isostasy. Topography can modify the local climate, for example through orographic precipitation, which in turn modifies the topography by changing the hydrologic regime in which it evolves. Many geomorphologists are particularly interested in the potential for feedbacks between climate and tectonics, mediated by geomorphic processes.[4]

In addition to these broad-scale questions, geomorphologists address issues that are more specific or more local. Glacial geomorphologists investigate glacial deposits such as moraines, eskers, and proglacial lakes, as well as glacial erosional features, to build chronologies of both small glaciers and large ice sheets and understand their motions and effects upon the landscape. Fluvial geomorphologists focus on rivers, how they transport sediment, migrate across the landscape, cut into bedrock, respond to environmental and tectonic changes, and interact with humans. Soils geomorphologists investigate soil profiles and chemistry to learn about the history of a particular landscape and understand how climate, biota, and rock interact. Other geomorphologists study how hillslopes form and change. Still others investigate the relationships between ecology and geomorphology. Because geomorphology is defined to comprise everything related to the surface of the Earth and its modification, it is a broad field with many facets.

Geomorphologists use a wide range of techniques in their work. These may include fieldwork and field data collection, the interpretation of remotely sensed data, geochemical analyses, and the numerical modelling of the physics of landscapes. Geomorphologists may rely on geochronology, using dating methods to measure the rate of changes to the surface.[5][6] Terrain measurement techniques are vital to quantitatively describe the form of the Earth's surface, and include differential GPS, remotely sensed digital terrain models and laser scanning, to quantify, study, and to generate illustrations and maps.[7]

Practical applications of geomorphology include hazard assessment (such as landslide prediction and mitigation), river control and stream restoration, and coastal protection.

Planetary geomorphology studies landforms on other terrestrial planets such as Mars. Indications of effects of wind, fluvial, glacial, mass wasting, meteor impact, tectonics and volcanic processes are studied.[8] This effort not only helps better understand the geologic and atmospheric history of those planets but also extends geomorphological study of the Earth. Planetary geomorphologists often use Earth analogues to aid in their study of surfaces of other planets.[9]

History

[edit]
"Cono de Arita" at the dry lake Salar de Arizaro on the Atacama Plateau, in northwestern Argentina. The cone itself is a volcanic edifice, representing complex interaction of intrusive igneous rocks with the surrounding salt.[10]
Lake "Veľké Hincovo pleso" in High Tatras, Slovakia. The lake occupies an "overdeepening" carved by flowing ice that once occupied this glacial valley.

Other than some notable exceptions in antiquity, geomorphology is a relatively young science, growing along with interest in other aspects of the earth sciences in the mid-19th century. This section provides a very brief outline of some of the major figures and events in its development.

Ancient geomorphology

[edit]

The study of landforms and the evolution of the Earth's surface can be dated back to scholars of Classical Greece. In the 5th century BC, Greek historian Herodotus argued from observations of soils that the Nile delta was actively growing into the Mediterranean Sea, and estimated its age.[11][12] In the 4th century BC, Greek philosopher Aristotle speculated that due to sediment transport into the sea, eventually those seas would fill while the land lowered. He claimed that this would mean that land and water would eventually swap places, whereupon the process would begin again in an endless cycle.[11][13] The Encyclopedia of the Brethren of Purity published in Arabic at Basra during the 10th century also discussed the cyclical changing positions of land and sea with rocks breaking down and being washed into the sea, their sediment eventually rising to form new continents.[13] The medieval Persian Muslim scholar Abū Rayhān al-Bīrūnī (973–1048), after observing rock formations at the mouths of rivers, hypothesized that the Indian Ocean once covered all of India.[14] In his De Natura Fossilium of 1546, German metallurgist and mineralogist Georgius Agricola (1494–1555) wrote about erosion and natural weathering.[15]

Another early theory of geomorphology was devised by Song dynasty Chinese scientist and statesman Shen Kuo (1031–1095). This was based on his observation of marine fossil shells in a geological stratum of a mountain hundreds of miles from the Pacific Ocean. Noticing bivalve shells running in a horizontal span along the cut section of a cliffside, he theorized that the cliff was once the pre-historic location of a seashore that had shifted hundreds of miles over the centuries. He inferred that the land was reshaped and formed by soil erosion of the mountains and by deposition of silt, after observing strange natural erosions of the Taihang Mountains and the Yandang Mountain near Wenzhou.[16][17][18] Furthermore, he promoted the theory of gradual climate change over centuries of time once ancient petrified bamboos were found to be preserved underground in the dry, northern climate zone of Yanzhou, which is now modern day Yan'an, Shaanxi province.[17][19][20] Previous Chinese authors also presented ideas about changing landforms. Scholar-official Du Yu (222–285) of the Western Jin dynasty predicted that two monumental stelae recording his achievements, one buried at the foot of a mountain and the other erected at the top, would eventually change their relative positions over time as would hills and valleys.[13] Daoist alchemist Ge Hong (284–364) created a fictional dialogue where the immortal Magu explained that the territory of the East China Sea was once a land filled with mulberry trees.[21]

Early modern geomorphology

[edit]

The term geomorphology seems to have been first used by Laumann in an 1858 work written in German. Keith Tinkler has suggested that the word came into general use in English, German and French after John Wesley Powell and W. J. McGee used it during the International Geological Conference of 1891.[22] John Edward Marr in his The Scientific Study of Scenery[23] considered his book as, 'an Introductory Treatise on Geomorphology, a subject which has sprung from the union of Geology and Geography'.

An early popular geomorphic model was the geographical cycle or cycle of erosion model of broad-scale landscape evolution developed by William Morris Davis between 1884 and 1899.[11] It was an elaboration of the uniformitarianism theory that had first been proposed by James Hutton (1726–1797).[24] With regard to valley forms, for example, uniformitarianism posited a sequence in which a river runs through a flat terrain, gradually carving an increasingly deep valley, until the side valleys eventually erode, flattening the terrain again, though at a lower elevation. It was thought that tectonic uplift could then start the cycle over. In the decades following Davis's development of this idea, many of those studying geomorphology sought to fit their findings into this framework, known today as "Davisian".[24] Davis's ideas are of historical importance, but have been largely superseded today, mainly due to their lack of predictive power and qualitative nature.[24]

In the 1920s, Walther Penck developed an alternative model to Davis's.[24] Penck thought that landform evolution was better described as an alternation between ongoing processes of uplift and denudation, as opposed to Davis's model of a single uplift followed by decay.[25] He also emphasised that in many landscapes slope evolution occurs by backwearing of rocks, not by Davisian-style surface lowering, and his science tended to emphasise surface process over understanding in detail the surface history of a given locality. Penck was German, and during his lifetime his ideas were at times rejected vigorously by the English-speaking geomorphology community.[24] His early death, Davis' dislike for his work, and his at-times-confusing writing style likely all contributed to this rejection.[26]

Both Davis and Penck were trying to place the study of the evolution of the Earth's surface on a more generalized, globally relevant footing than it had been previously. In the early 19th century, authors – especially in Europe – had tended to attribute the form of landscapes to local climate, and in particular to the specific effects of glaciation and periglacial processes. In contrast, both Davis and Penck were seeking to emphasize the importance of evolution of landscapes through time and the generality of the Earth's surface processes across different landscapes under different conditions.

During the early 1900s, the study of regional-scale geomorphology was termed "physiography".[27] Physiography later was considered to be a contraction of "physical" and "geography", and therefore synonymous with physical geography, and the concept became embroiled in controversy surrounding the appropriate concerns of that discipline. Some geomorphologists held to a geological basis for physiography and emphasized a concept of physiographic regions while a conflicting trend among geographers was to equate physiography with "pure morphology", separated from its geological heritage.[citation needed] In the period following World War II, the emergence of process, climatic, and quantitative studies led to a preference by many earth scientists for the term "geomorphology" in order to suggest an analytical approach to landscapes rather than a descriptive one.[28]

Climatic geomorphology

[edit]
Further information: Climatic geomorphology

During the age of New Imperialism in the late 19th century European explorers and scientists traveled across the globe bringing descriptions of landscapes and landforms. As geographical knowledge increased over time these observations were systematized in a search for regional patterns. Climate emerged thus as prime factor for explaining landform distribution at a grand scale. The rise of climatic geomorphology was foreshadowed by the work of Wladimir Köppen, Vasily Dokuchaev and Andreas Schimper. William Morris Davis, the leading geomorphologist of his time, recognized the role of climate by complementing his "normal" temperate climate cycle of erosion with arid and glacial ones.[29][30] Nevertheless, interest in climatic geomorphology was also a reaction against Davisian geomorphology that was by the mid-20th century considered both un-innovative and dubious.[30][31] Early climatic geomorphology developed primarily in continental Europe while in the English-speaking world the tendency was not explicit until L.C. Peltier's 1950 publication on a periglacial cycle of erosion.[29]

Climatic geomorphology was criticized in a 1969 review article by process geomorphologist D.R. Stoddart.[30][32] The criticism by Stoddart proved "devastating" sparking a decline in the popularity of climatic geomorphology in the late 20th century.[30][32] Stoddart criticized climatic geomorphology for applying supposedly "trivial" methodologies in establishing landform differences between morphoclimatic zones, being linked to Davisian geomorphology and by allegedly neglecting the fact that physical laws governing processes are the same across the globe.[32] In addition some conceptions of climatic geomorphology, like that which holds that chemical weathering is more rapid in tropical climates than in cold climates proved to not be straightforwardly true.[30]

Quantitative and process geomorphology

[edit]
Part of the Great Escarpment in the Drakensberg, southern Africa. This landscape, with its high altitude plateau being incised into by the steep slopes of the escarpment, was cited by Davis as a classic example of his cycle of erosion.[33]

Geomorphology was started to be put on a solid quantitative footing in the middle of the 20th century. Following the early work of Grove Karl Gilbert around the turn of the 20th century,[11][24][25] a group of mainly American natural scientists, geologists and hydraulic engineers including William Walden Rubey, Ralph Alger Bagnold, Hans Albert Einstein, Frank Ahnert, John Hack, Luna Leopold, A. Shields, Thomas Maddock, Arthur Strahler, Stanley Schumm, and Ronald Shreve began to research the form of landscape elements such as rivers and hillslopes by taking systematic, direct, quantitative measurements of aspects of them and investigating the scaling of these measurements.[11][24][25][34] These methods began to allow prediction of the past and future behavior of landscapes from present observations, and were later to develop into the modern trend of a highly quantitative approach to geomorphic problems. Many groundbreaking and widely cited early geomorphology studies appeared in the Bulletin of the Geological Society of America,[35] and received only few citations prior to 2000 (they are examples of "sleeping beauties")[36] when a marked increase in quantitative geomorphology research occurred.[37]

Quantitative geomorphology can involve fluid dynamics and solid mechanics, geomorphometry, laboratory studies, field measurements, theoretical work, and full landscape evolution modeling. These approaches are used to understand weathering and the formation of soils, sediment transport, landscape change, and the interactions between climate, tectonics, erosion, and deposition.[38][39]

In Sweden Filip Hjulström's doctoral thesis, "The River Fyris" (1935), contained one of the first quantitative studies of geomorphological processes ever published. His students followed in the same vein, making quantitative studies of mass transport (Anders Rapp), fluvial transport (Åke Sundborg), delta deposition (Valter Axelsson), and coastal processes (John O. Norrman). This developed into "the Uppsala School of Physical Geography".[40]

Contemporary geomorphology

[edit]

Today, the field of geomorphology encompasses a very wide range of different approaches and interests.[11] Modern researchers aim to draw out quantitative "laws" that govern Earth surface processes, but equally, recognize the uniqueness of each landscape and environment in which these processes operate. Particularly important realizations in contemporary geomorphology include:

1) that not all landscapes can be considered as either "stable" or "perturbed", where this perturbed state is a temporary displacement away from some ideal target form. Instead, dynamic changes of the landscape are now seen as an essential part of their nature.[38][41]
2) that many geomorphic systems are best understood in terms of the stochasticity of the processes occurring in them, that is, the probability distributions of event magnitudes and return times.[42][43] This in turn has indicated the importance of chaotic determinism to landscapes, and that landscape properties are best considered statistically.[44] The same processes in the same landscapes do not always lead to the same end results.

According to Karna Lidmar-Bergström, regional geography is since the 1990s no longer accepted by mainstream scholarship as a basis for geomorphological studies.[45]

Albeit having its importance diminished, climatic geomorphology continues to exist as field of study producing relevant research. More recently concerns over global warming have led to a renewed interest in the field.[30]

Despite considerable criticism, the cycle of erosion model has remained part of the science of geomorphology.[46] The model or theory has never been proved wrong,[46] but neither has it been proven.[47] The inherent difficulties of the model have instead made geomorphological research to advance along other lines.[46] In contrast to its disputed status in geomorphology, the cycle of erosion model is a common approach used to establish denudation chronologies, and is thus an important concept in the science of historical geology.[48] While acknowledging its shortcomings, modern geomorphologists Andrew Goudie and Karna Lidmar-Bergström have praised it for its elegance and pedagogical value respectively.[49][50]

Processes

[edit]
Gorge cut by the Indus River into bedrock, Nanga Parbat region, Pakistan. This is the deepest river canyon in the world. Nanga Parbat itself, the world's 9th highest mountain, is seen in the background.

Geomorphically relevant processes generally fall into (1) the production of regolith by weathering and erosion, (2) the transport of that material, and (3) its eventual deposition. Primary surface processes responsible for most topographic features include wind, waves, chemical dissolution, mass wasting, groundwater movement, surface water flow, glacial action, tectonism, and volcanism. Other more exotic geomorphic processes might include periglacial (freeze-thaw) processes, salt-mediated action, changes to the seabed caused by marine currents, seepage of fluids through the seafloor or extraterrestrial impact.

Aeolian processes

[edit]
Wind-eroded alcove near Moab, Utah

Aeolian processes pertain to the activity of the winds and more specifically, to the winds' ability to shape the surface of the Earth. Winds may erode, transport, and deposit materials, and are effective agents in regions with sparse vegetation and a large supply of fine, unconsolidated sediments. Although water and mass flow tend to mobilize more material than wind in most environments, aeolian processes are important in arid environments such as deserts.[51]

Biological processes

[edit]
Beaver dams, as this one in Tierra del Fuego, constitute a specific form of zoogeomorphology, a type of biogeomorphology.

The interaction of living organisms with landforms, or biogeomorphologic processes, can be of many different forms, and is probably of profound importance for the terrestrial geomorphic system as a whole. Biology can influence very many geomorphic processes, ranging from biogeochemical processes controlling chemical weathering, to the influence of mechanical processes like burrowing and tree throw on soil development, to even controlling global erosion rates through modulation of climate through carbon dioxide balance. Terrestrial landscapes in which the role of biology in mediating surface processes can be definitively excluded are extremely rare, but may hold important information for understanding the geomorphology of other planets, such as Mars.[52]

Fluvial processes

[edit]
Seif and barchan dunes in the Hellespontus region on the surface of Mars. Dunes are mobile landforms formed by the transport of large volumes of sand by wind.
Main article: Fluvial
See also: Hack's law and Sediment transport

Rivers and streams are not only conduits of water, but also of sediment. The water, as it flows over the channel bed, is able to mobilize sediment and transport it downstream, either as bed load, suspended load or dissolved load. The rate of sediment transport depends on the availability of sediment itself and on the river's discharge.[53] Rivers are also capable of eroding into rock and forming new sediment, both from their own beds and also by coupling to the surrounding hillslopes. In this way, rivers are thought of as setting the base level for large-scale landscape evolution in nonglacial environments.[54][55] Rivers are key links in the connectivity of different landscape elements.

As rivers flow across the landscape, they generally increase in size, merging with other rivers. The network of rivers thus formed is a drainage system. These systems take on four general patterns: dendritic, radial, rectangular, and trellis. Dendritic happens to be the most common, occurring when the underlying stratum is stable (without faulting). Drainage systems have four primary components: drainage basin, alluvial valley, delta plain, and receiving basin. Some geomorphic examples of fluvial landforms are alluvial fans, oxbow lakes, and fluvial terraces.

Glacial processes

[edit]
Features of a glacial landscape

Glaciers, while geographically restricted, are effective agents of landscape change. The gradual movement of ice down a valley causes abrasion and plucking of the underlying rock. Abrasion produces fine sediment, termed glacial flour. The debris transported by the glacier, when the glacier recedes, is termed a moraine. Glacial erosion is responsible for U-shaped valleys, as opposed to the V-shaped valleys of fluvial origin.[56]

The way glacial processes interact with other landscape elements, particularly hillslope and fluvial processes, is an important aspect of Plio-Pleistocene landscape evolution and its sedimentary record in many high mountain environments. Environments that have been relatively recently glaciated but are no longer may still show elevated landscape change rates compared to those that have never been glaciated. Nonglacial geomorphic processes which nevertheless have been conditioned by past glaciation are termed paraglacial processes. This concept contrasts with periglacial processes, which are directly driven by formation or melting of ice or frost.[57]

Hillslope processes

[edit]
Talus cones on the north shore of Isfjorden, Svalbard, Norway. Talus cones are accumulations of coarse hillslope debris at the foot of the slopes producing the material.
The Ferguson Slide is an active landslide in the Merced River canyon on California State Highway 140, a primary access road to Yosemite National Park.

Soil, regolith, and rock move downslope under the force of gravity via creep, slides, flows, topples, and falls. Such mass wasting occurs on both terrestrial and submarine slopes, and has been observed on Earth, Mars, Venus, Titan and Iapetus.

Ongoing hillslope processes can change the topology of the hillslope surface, which in turn can change the rates of those processes. Hillslopes that steepen up to certain critical thresholds are capable of shedding extremely large volumes of material very quickly, making hillslope processes an extremely important element of landscapes in tectonically active areas.[58]

On the Earth, biological processes such as burrowing or tree throw may play important roles in setting the rates of some hillslope processes.[59]

Igneous processes

[edit]

Both volcanic (eruptive) and plutonic (intrusive) igneous processes can have important impacts on geomorphology. The action of volcanoes tends to rejuvenize landscapes, covering the old land surface with lava and tephra, releasing pyroclastic material and forcing rivers through new paths. The cones built by eruptions also build substantial new topography, which can be acted upon by other surface processes. Plutonic rocks intruding then solidifying at depth can cause both uplift or subsidence of the surface, depending on whether the new material is denser or less dense than the rock it displaces.

Tectonic processes

[edit]
See also: Erosion and tectonics

Tectonic effects on geomorphology can range from scales of millions of years to minutes or less. The effects of tectonics on landscape are heavily dependent on the nature of the underlying bedrock fabric that more or less controls what kind of local morphology tectonics can shape. Earthquakes can, in terms of minutes, submerge large areas of land forming new wetlands. Isostatic rebound can account for significant changes over hundreds to thousands of years, and allows erosion of a mountain belt to promote further erosion as mass is removed from the chain and the belt uplifts. Long-term plate tectonic dynamics give rise to orogenic belts, large mountain chains with typical lifetimes of many tens of millions of years, which form focal points for high rates of fluvial and hillslope processes and thus long-term sediment production.

Features of deeper mantle dynamics such as plumes and delamination of the lower lithosphere have also been hypothesised to play important roles in the long term (> million year), large scale (thousands of km) evolution of the Earth's topography (see dynamic topography). Both can promote surface uplift through isostasy as hotter, less dense, mantle rocks displace cooler, denser, mantle rocks at depth in the Earth.[60][61]

Marine processes

[edit]

Marine processes are those associated with the action of waves, marine currents and seepage of fluids through the seafloor. Mass wasting and submarine landsliding are also important processes for some aspects of marine geomorphology.[62] Because ocean basins are the ultimate sinks for a large fraction of terrestrial sediments, depositional processes and their related forms (e.g., sediment fans, deltas) are particularly important as elements of marine geomorphology.

Overlap with other fields

[edit]

There is a considerable overlap between geomorphology and other fields. Deposition of material is extremely important in sedimentology. Weathering is the chemical and physical disruption of earth materials in place on exposure to atmospheric or near surface agents, and is typically studied by soil scientists and environmental chemists, but is an essential component of geomorphology because it is what provides the material that can be moved in the first place. Civil and environmental engineers are concerned with erosion and sediment transport, especially related to canals, slope stability (and natural hazards), water quality, coastal environmental management, transport of contaminants, and stream restoration. Glaciers can cause extensive erosion and deposition in a short period of time, making them extremely important entities in the high latitudes and meaning that they set the conditions in the headwaters of mountain-born streams; glaciology therefore is important in geomorphology.

See also

[edit]

References

[edit]

Further reading

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Geomorphology

View on Grokipedia
from Grokipedia
Geomorphology is the of landforms—their origin, , distribution, and the physical, chemical, and biological processes that shape the Earth's surface over various timescales, from recent centuries to billions of years. This discipline, derived from words geo (earth), morphē (form), and logos (discourse), focuses primarily on surficial features formed during the period (the last 2.6 million years), though it extends to older landscapes influenced by tectonic and erosional histories. At its core, geomorphology examines the interplay between endogenic processes, driven by internal Earth forces such as , , and faulting that build and uplift landforms like mountains and plateaus, and exogenic processes, powered by external agents including , , transportation, and deposition by , wind, ice, and gravity that sculpt and degrade these features. For instance, fluvial systems carve valleys and floodplains through , while glacial activity forms cirques, moraines, and drumlins during ice ages. Key principles guiding the field include , which posits that present-day processes operating at observable rates have shaped landscapes throughout geologic time—"the present is the key to the past"—and, to a lesser extent, , recognizing rare but transformative events like massive volcanic eruptions or meteor impacts. The scope of geomorphology spans immense scales, from global continents (10^7 km²) to microscopic soil features (10^{-8} km²), and integrates insights from , , , and to model dynamics. Subfields include tectonic geomorphology, which links fault movements to seismic hazards; fluvial geomorphology, studying riverine evolution; aeolian geomorphology, analyzing wind-driven dunes and deserts; and coastal geomorphology, addressing shoreline changes from waves and sea-level rise. Historically, the field evolved from early descriptive works by figures like in 450 BCE to modern quantitative approaches pioneered in the by and G.K. Gilbert, emphasizing cycles of and process-response systems. Geomorphology holds practical significance in assessing natural hazards such as landslides, floods, and earthquakes, predicting environmental changes due to variability, and informing , , and engineering projects. Human activities, including , , and , now rival natural processes in altering landscapes, moving approximately 57 billion tonnes of material annually—far exceeding global rates of 26 billion tonnes—thus amplifying by factors of 10 to 100 times in affected areas. Through tools like digital elevation models, , and process simulations, geomorphologists continue to unravel the dynamic equilibrium of 's surface, revealing how past events inform future sustainability.

Introduction

Definition and Core Principles

Geomorphology is the scientific study of landforms and the processes—physical, chemical, and biological—that originate, evolve, and modify them on 's surface. This discipline examines the dynamics of surface features, such as mountains and river valleys, integrating observations of contemporary processes to interpret past landscapes. The term derives from the Greek roots geo (Earth), morphe (form), and (study), reflecting its focus on the forms and shaping forces of the terrestrial environment. A foundational principle of geomorphology is , which posits that the physical and chemical processes observable today have operated similarly throughout geological time, allowing modern observations to elucidate ancient development. Closely allied is , emphasizing that the same natural laws and processes govern Earth's surface now as in the past, provided conditions are comparable. These principles, first articulated by figures like and , underpin the inference of historical geomorphic events from present-day evidence. Additionally, geomorphology employs , viewing landforms as components of open systems characterized by continuous inputs (e.g., , ), internal feedbacks, and outputs (e.g., ), which drive dynamic equilibrium and change. Geomorphological inquiry distinguishes between descriptive approaches, which catalog landform morphology and spatial patterns, and genetic approaches, which emphasize the causal processes—such as or deposition—that generate and alter those forms. The descriptive method provides a baseline inventory of features like fluvial channels, while the genetic perspective integrates process mechanics to explain their evolution, fostering a holistic understanding of landscape dynamics. This duality ensures comprehensive analysis without conflating form with its underlying mechanisms.

Scope and Importance

Geomorphology encompasses the study of landforms and the processes that shape them across diverse environments, including terrestrial landscapes such as mountains, valleys, and plains; coastal features like beaches, cliffs, and deltas; and submarine terrains encompassing continental shelves, canyons, and abyssal plains. This discipline integrates principles from physical geography, geology, and environmental science to analyze both contemporary surface dynamics and paleogeomorphic records of ancient landscapes, employing methods like stratigraphy and dating techniques to reconstruct Earth’s surface evolution over geological timescales. The importance of geomorphology lies in its capacity to predict landscape responses to environmental changes, particularly climate variability, by modeling phenomena such as sea-level rise and glacial retreat, which inform adaptive strategies for ecosystems and human settlements. It plays a pivotal role in through terrain mapping and assessments, supports by quantifying rates in agricultural areas, and aids disaster mitigation by identifying risks from landslides, floods, and , thereby reducing economic losses estimated in billions annually from such events. For instance, geomorphic analysis has guided in regions like the , enhancing agricultural productivity. Interdisciplinarily, geomorphology bridges Earth surface processes with human activities, influencing urban development by evaluating foundation stability in expansive cities and operations by assessing impacts on rivers and . This integration extends to economic sectors, where it optimizes resource extraction, such as and sand for , while minimizing . In modern contexts, geomorphology contributes to the (SDGs), particularly SDG 13 () through hazard mapping for and risks, SDG 11 (sustainable cities and communities) via resilient planning, and SDG 15 (life on land) by promoting and protection in and coastal zones. These efforts align with global frameworks for , fostering sustainable and resilience worldwide.

Historical Development

Ancient and Pre-Modern Contributions

Early contributions to geomorphology emerged from ancient civilizations, where observations of landforms were intertwined with philosophical, mythological, and practical concerns rather than systematic scientific inquiry. In , (c. 484–425 BCE) provided one of the earliest recorded descriptions of erosional processes, noting how the River's sediment deposition formed its delta through gradual buildup over centuries, attributing this to the river's transport of from upstream highlands. Similarly, (c. 64 BCE–24 CE), in his , described along coastlines and river valleys, observing how waves and currents sculpted shorelines and how from eroding hills contributed to alluvial plains, emphasizing the dynamic interplay between land and water. These accounts, drawn from travel and empirical observation, laid descriptive groundwork for understanding landscape change, though they often invoked divine or cyclical explanations. Parallel developments occurred in ancient China, where texts from the (475–221 BCE) documented landscape evolution, particularly the shifting courses of the (Huang He). The Shui Jing Zhu (Commentary on the Water Classic), compiled in the early 6th century CE by Li Daoyuan during the Dynasty but drawing on the earlier Shui Jing from the CE and prior observations, detailed how floods and sediment loads caused the river to alter its path dramatically, eroding banks and depositing soils across the , influencing agricultural practices and flood control strategies. These records highlighted the river's role in shaping vast alluvial landscapes, reflecting a pragmatic focus on human-land interactions amid environmental variability. During the Medieval and periods, interpretations of landforms often blended empirical sketches with religious or mythological frameworks. (1452–1519), in his notebooks, sketched detailed illustrations of river meandering and processes, depicting how water carved valleys and transported downstream, predating formal geological theories by centuries; he argued that mountains were worn down by rivers over time, forming fertile plains. Biblical and mythological views, prevalent in medieval , portrayed landscapes as divinely shaped or remnants of cataclysmic events like the , as seen in interpretations of narratives that explained valleys and strata as flood-deposited features, influencing early perceptions of Earth's surface without rigorous testing. In the 17th and 18th centuries, more empirical approaches began to emerge, bridging observation with nascent scientific principles. Nicolaus Steno (1638–1686), a Danish anatomist and geologist, proposed principles of in his 1669 work De solido intra solidum naturaliter contento dissertationis prodromus, applying them to landforms by explaining how sedimentary layers in mountains and valleys formed sequentially through deposition and , providing a framework for interpreting landscape history. Contemporaries recognized evidence as indicators of past landscapes; for instance, Robert Hooke's 1665 Micrographia and later writings discussed marine shells found inland as proof of ancient seas covering continents, suggesting that current landforms resulted from prolonged environmental changes. These ideas marked a shift toward -based reasoning, though still qualitative. Overall, ancient and pre-modern contributions to geomorphology were predominantly descriptive, qualitative, and speculative, relying on direct observation without experimental validation or quantitative models, which limited their predictive power. This foundational work set the stage for the more systematic investigations of the modern era, exemplified by figures like James Hutton.

19th-Century Foundations

The 19th century marked the transition of geomorphology from descriptive observations to a structured scientific discipline, largely through the application of uniformitarian principles to landscape evolution. Charles Lyell, in his seminal work Principles of Geology published between 1830 and 1833, reinforced uniformitarianism by arguing that the Earth's surface features result from gradual, ongoing processes operating at rates observable today, rather than sudden catastrophic events. This framework shifted focus from static interpretations of landforms to dynamic ones, emphasizing slow, uniform changes driven by erosion, deposition, and tectonic uplift over vast timescales. Lyell's ideas provided a foundational methodology for later geomorphologists, promoting empirical observation and the rejection of supernatural explanations in favor of natural laws. Building on this, emerged as a pivotal figure in the late , developing the model that conceptualized landscape evolution as a predictable sequence of stages. In his 1899 paper "The Geographical Cycle," Davis described landform development progressing from youth—characterized by steep slopes, V-shaped valleys, and active downcutting—to maturity with gentler slopes and broader valleys, and finally to old age, where a (near-flat surface) forms through prolonged erosion. This model assumed tectonic uplift initiates the cycle, followed by fluvial erosion dominating under stable conditions until base level is approached. Davis's approach established geomorphology as a deductive , integrating empirical with theoretical prediction to explain regional landscapes. Central to Davisian geomorphology was the triad of , , and time, which framed analysis as a function of underlying geological framework (), erosional agents (), and duration of development (time). refers to rock type, , and initial ; encompasses and fluvial action; and time determines the stage of . This stage-based model highlighted how time acts as a maturational factor, allowing landscapes to "age" predictably under constant conditions, influencing subsequent classifications and evolutionary theories in the field. Other notable contributions included John Wesley Powell's explorations of arid landforms in during the , which emphasized the role of episodic fluvial processes and structural controls in shaping dryland features like canyons and plateaus. Through his surveys for the U.S. Geological Survey, Powell documented how limits continuous , leading to distinct assemblages dependent on sparse but intense water flows and resistant . His work complemented Davis's fluvial focus by recognizing fluvial dominance in temperate, humid climates, where steady rainfall sustains river incision and valley widening as primary shapers of . Debates in 19th-century geomorphology often centered on static versus dynamic views of landscapes, with Lyell's implying equilibrium states challenged by Davis's evolutionary cycle, which portrayed as transient and progressive. Early classifications of by origin also gained traction, categorizing features genetically as tectonic, erosional, or depositional to discern formative processes from superficial appearances. These discussions laid groundwork for distinguishing types based on their developmental history, fostering a more analytical approach to geomorphic interpretation.

20th-Century Paradigms

The marked a pivotal era in geomorphology, characterized by challenges to 19th-century qualitative models and the emergence of paradigms emphasizing climatic controls, quantitative methods, and process dynamics. Building on Davis's as a foundational but critiqued framework for landscape evolution, geomorphologists increasingly incorporated endogenic and exogenic factors to explain development more dynamically. Climatic geomorphology gained prominence in the early , focusing on how zones shape distinct assemblages through differential and rates. Walther Penck's 1924 work, Morphologische Analyse der Landformen, proposed a model of through parallel retreat and convex-upward profiles, driven by continuous tectonic uplift and climatic influences, contrasting sharply with Davis's emphasis on declining slopes and sequential maturity stages. Penck argued that landforms maintain equilibrium via ongoing uplift counterbalanced by erosion, influencing subsequent debates on steady-state landscapes in tectonically active regions. In the mid-20th century, Julius Büdel advanced climatic geomorphology by integrating field observations from diverse environments to theorize on periglacial and tropical landscape formation. During the 1940s and 1950s, Büdel's studies in highlighted periglacial processes like solifluction and frost wedging as key to forming blockfields and in cold climates, while his 1950s-1960s research in and emphasized deep chemical in humid , leading to laterite profiles and landscapes. Büdel's 1982 synthesis, Climatic Geomorphology, formalized ten morphogenetic regimes—from glacial to tropical—asserting that 95% of mid-latitude landforms are relict features inherited from past climates, underscoring the role of climatic oscillations in global relief. Post-World War II, the quantitative revolution transformed geomorphology from descriptive narratives to empirical, measurement-based analysis, enabling testable hypotheses on process rates and form-function relationships. This shift, accelerating in the 1950s, drew on advances in and statistics to quantify landscape responses. Luna Leopold's 1953 collaboration with Thomas Maddock introduced hydraulic geometry, demonstrating that river channel width, depth, velocity, and sediment load scale predictably with discharge via power-law relationships (e.g., width ∝ discharge^{0.5}), providing a framework for predicting fluvial adjustments across basins. Concurrently, emerged in the 1960s, viewing landscapes as open systems with inputs, outputs, and feedbacks; R.J. Chorley's 1962 USGS paper applied general to geomorphology, modeling landforms as hierarchical structures responsive to energy and mass fluxes, which facilitated interdisciplinary integrations with and . Process geomorphology further refined these approaches by emphasizing discrete events and nonlinear behaviors over gradual change. Stanley Schumm's research on alluvial rivers introduced the concept of river metamorphosis, where channels abruptly shift form—such as from meandering to braided—due to changes in load or discharge, as observed in Australian catchments like the . Building on this, Schumm's 1973 work formalized geomorphic thresholds as critical points where small perturbations trigger disproportionate responses, and complex responses as lagged, episodic adjustments (e.g., initial followed by incision), challenging equilibrium assumptions and informing river management. The acceptance of in the late revolutionized geomorphological understanding of uplift and by linking surface processes to global lithospheric dynamics. This paradigm shift, solidified by evidence from and earthquake patterns, explained how convergent margins drive orogenic uplift, enhancing rates and preserving high-relief landscapes, as seen in the where tectonic rates outpace . It integrated endogenic drivers into exogenic models, fostering holistic views of landscape evolution over geological timescales.

21st-Century Advances

The integration of geographic information systems (GIS) and technologies has revolutionized geomorphological mapping in the 21st century, enabling high-resolution analysis of landforms and processes. Post-2010 advancements in (Light Detection and Ranging) have provided airborne and terrestrial data yielding digital models (DEMs) at resolutions of 1 meter or finer, facilitating precise detection of geomorphic changes such as landslides and patterns. For instance, multi-temporal LiDAR-derived DEMs from the USGS 3D Program (3DEP) allow for the creation of DEMs of Difference (DoD) to quantify vertical displacements with sub-meter accuracy, as demonstrated in studies of watersheds covering over 2,000 km². , including from missions like TanDEM-X and global ensembles such as GEDTM30 at 30-meter resolution, complements LiDAR by offering broad-scale topographic data essential for modeling landscape evolution and hazard assessment. Applications of nonlinear dynamics and have advanced landscape evolution models by incorporating and sensitivity to initial conditions, revealing the complex, aperiodic behaviors of geomorphic systems. Seminal work on delta networks demonstrates that bifurcations in fluvial systems can produce chaotic dynamics, with positive Lyapunov exponents indicating short-term predictability limits around one avulsion timescale, while longer-term statistical patterns like rates remain compensable. This approach extends earlier quantitative foundations, emphasizing in processes such as river avulsions and hillslope adjustments, where small perturbations lead to disproportionate landscape responses. High-impact models now simulate these nonlinear interactions to forecast evolutionary pathways, highlighting the role of feedback loops in maintaining dynamic equilibrium across scales. Anthropogenic geomorphology has emerged as a distinct subfield in the 21st century, systematically examining human-altered landforms amid accelerating and in the . Urban expansion modifies relief through excavation, filling, and creation, increasing runoff by 40–83% and exacerbating rates that exceed natural formation by over two orders of magnitude. Studies document widespread degradation affecting 25% of ice-free land and 1.3–3.2 billion people, with cropland and urban areas in regions like and showing annual soil losses up to 18 t ha⁻¹ due to and . In the 2020s, research emphasizes landscapes shaped by these forces, using GIS to map legacy effects like scars and , which disrupt natural geomorphic processes and amplify vulnerability to hazards. Geomorphologists have increasingly addressed global challenges through responses to IPCC assessments on climate-driven changes and comparative planetary studies. The IPCC's Special Report on Climate Change, , , and highlights accelerated from intensified rainfall, potentially increasing rates by 1.2–1,600%, compounded by human and leading to novel degradation in and arid zones. Reviews of modern climate effects confirm heightened slope instability and aeolian mobilization in regions like the , where extreme events and warming have triggered landslides and dust emissions rising 44–81% since the . Concurrently, data from missions like Perseverance and have advanced planetary geomorphology by revealing active processes such as aeolian dune fluxes (1–35 m³/m/year) and CO₂-driven slope gullies, offering Earth-analog insights into wind and frost regimes absent liquid water. These observations, integrated with orbital imagery, underscore self-similarities in aeolian and mass-wasting dynamics across planets, informing models of extraterrestrial landscape evolution.

Fundamental Concepts

Landforms and Their Classification

Landforms are the fundamental topographic features of the Earth's surface, shaped by the interaction of geomorphic agents such as , , , and tectonic forces, resulting in diverse structures that range from subtle depressions to prominent elevations. These features, including mountains, valleys, plateaus, and plains, represent the visible outcomes of endogenic and exogenic processes acting over various timescales, and they serve as the primary objects of study in geomorphology. Representative examples illustrate their scale: mountains often exceed 1,000 meters in height due to uplift, while plains form extensive low-relief areas through sediment accumulation. Classification of landforms employs several schemes to organize these features systematically, facilitating analysis of their distribution and characteristics. The genetic classification, pioneered by , categorizes landforms based on dominant formative processes, such as fluvial, glacial, or tectonic origins, emphasizing the role of structure, process, and time in their development. Morphometric classification, in contrast, relies on quantitative metrics of shape and , including , , and , to delineate features like ridges (high , steep slopes) from basins (low , concave forms). Hierarchical classification structures landforms across scales, from microscale elements like ripples (centimeter-scale bedforms) to mesoscale features such as hillslopes (hundreds of meters) and macroscale continental landmasses, allowing nested analysis of regional physiography. These schemes, often integrated in modern geomorphic mapping, draw from foundational works like Fenneman's physiographic divisions. Key types of landforms are broadly grouped by their primary mode of formation, providing an overview without delving into specific mechanisms. Erosional landforms, such as canyons and sea cliffs, result from the removal of material, creating incised or sculpted terrains with high relief. Depositional landforms, exemplified by deltas and alluvial fans, arise from sediment buildup, forming low-gradient accumulations that stabilize landscapes. Tectonic landforms, including fault scarps and rift valleys, stem from crustal movements, producing sharp linear features with significant vertical displacement, often on the order of hundreds of meters. This tripartite overview highlights how landforms reflect underlying geomorphic agents, with hybrids like volcanic plateaus combining multiple influences. Landforms are not static; they evolve through ongoing interactions of denudation, which encompasses and that lowers and smooths surfaces, and , the deposition of materials that builds and fills topographic lows. Over geological time, these processes lead to or degradation, as seen in the transformation of uplifted mountains into peneplains via prolonged , altering relief and form in response to climatic and tectonic shifts. Such evolution underscores the dynamic nature of geomorphology, where landforms transition between states influenced by external forcings.

Geomorphic Systems and Equilibrium

Geomorphology increasingly employs a systems approach to understand landscapes as interconnected open systems characterized by fluxes of and . In this framework, geomorphic systems receive inputs such as , tectonic uplift, and solar radiation, which drive processes like , , and deposition, ultimately leading to outputs including export and heat dissipation. This perspective emphasizes the holistic interactions within landscapes, where subsystems—such as hillslopes, channels, and floodplains—operate in tandem to shape landforms over various scales. A core concept within this systems view is dynamic equilibrium, where landscapes maintain a characteristic form through continuous adjustment to prevailing controls, despite ongoing changes in inputs and outputs. Proposed by Hack in his analysis of erosional in humid temperate regions, dynamic equilibrium posits that slopes, channels, and basins evolve to balance erosional and depositional forces, resulting in a stable morphology under constant environmental conditions. This contrasts with steady-state conditions, in which inputs precisely equal outputs, leading to no net change in system storage, versus transient states where imbalances cause evolution toward a new equilibrium. Geomorphic systems often exhibit thresholds, representing critical points beyond which abrupt changes occur, introducing complexity and nonlinearity. Schumm defined geomorphic thresholds as conditions inherent to the system where landform stability is exceeded, such as when increased triggers slope failure or channel incision without proportional shifts in external drivers like or . These thresholds highlight the role of feedbacks in self-regulation; for instance, negative feedbacks, like stabilizing slopes after initial , can restore balance, while positive feedbacks may amplify changes, leading to complex response sequences in landscape evolution. The foundational equation governing these systems is the mass balance principle, derived from the conservation of mass, which quantifies changes in sediment or material storage within a geomorphic unit. The equation is expressed as: ΔS=I−O\Delta S = I - O where ΔS\Delta S is the change in storage over a specified time interval, II represents inputs (e.g., sediment from upstream sources or hillslope delivery), and OO denotes outputs (e.g., downstream export or deposition). To derive this, consider a control volume in the landscape, such as a river reach or basin; by applying the continuity equation from fluid mechanics—stating that mass cannot be created or destroyed—the net accumulation or depletion results solely from the difference between influx and outflux rates. In steady-state equilibrium, ΔS=0\Delta S = 0, implying I=OI = O, whereas transient conditions yield ΔS≠0\Delta S \neq 0, driving system adjustment. This equation underpins quantitative analyses of landscape response to perturbations, such as tectonic uplift increasing II and prompting erosional outputs to reestablish balance.

Spatial and Temporal Scales

Geomorphic processes and landforms exhibit a across spatial scales, where phenomena at smaller scales contribute to patterns at larger ones. At the microscale, processes operate on dimensions of centimeters to meters, such as particle interactions and microtopographic features like rills or individual sites. The mesoscale encompasses hillslopes, small catchments, and valley segments on the order of hundreds of meters to a few kilometers, where processes like soil creep and localized dominate and begin to aggregate into broader units. At the macroscale, entire drainage basins or regional assemblages span tens to hundreds of kilometers, integrating the effects of smaller-scale dynamics to produce large-scale patterns such as mountain belts or fluvial networks. This implies that microscale processes, while seemingly local, propagate upward to shape macroscale morphology through nonlinear interactions and feedback loops. Temporal scales in geomorphology similarly span orders of magnitude, reflecting the duration over which processes influence landforms. Short-term scales involve discrete events lasting hours to days, such as floods or landslides that rapidly alter channel morphology or deposit pulses. Medium-term scales cover seasonal to decadal cycles, including responses to annual variations or changes that adjust hillslope stability and . Long-term scales extend to thousands or millions of years, encompassing tectonic uplift, climatic shifts, and overall , with rates typically ranging from 0.01 to 1 mm/yr in diverse settings like mountain fronts or stable cratons. These rates provide context for evolution, as higher values (e.g., approaching 1 mm/yr) often occur in tectonically active regions, while lower ones prevail in low-relief areas. The integration of spatial and temporal scales reveals fundamental challenges and principles in geomorphology, particularly through space-time scaling laws that describe how process intensities and outcomes vary across dimensions. For instance, short-term events at microscales may appear random but aggregate into predictable long-term patterns at macroscales, as seen in models. Upscaling process data from field measurements to regional models is complicated by nonlinearities, often addressed using geometry, which quantifies the self-similar irregularity of landscapes—such as networks or coastlines—with fractal dimensions typically between 1.2 and 1.5, indicating scale-invariant roughness. A key distinction arises in the drivers of change: allogenic factors, like external or tectonic forcings, dominate at longer temporal and larger spatial scales, while autogenic processes, such as internal channel migrations or autotrophic feedbacks, prevail at shorter and smaller scales, blurring boundaries where both interact. Equilibrium states in geomorphic systems, such as dynamic stability in profiles, thus emerge as scale-dependent, varying from transient balances at event scales to quasi-steady configurations over geological epochs.

Endogenic Processes

Tectonic Processes

Tectonic processes represent the primary endogenic forces that deform and elevate , fundamentally shaping large-scale geomorphic features through internal dynamics. These processes are predominantly driven by , the theory that Earth's is divided into rigid plates that move relative to one another, powered by . At convergent plate boundaries, where plates collide, crustal shortening leads to the formation of mountain belts via folding and thrusting; for instance, the ongoing collision between the Indian and Eurasian plates has produced the Himalayan orogen. Divergent boundaries, such as the , involve crustal extension and thinning, resulting in rift valleys and elevated rift shoulders due to normal faulting. Transform boundaries, like the , facilitate lateral sliding of plates, generating strike-slip faulting that offsets landforms and creates linear escarpments. Isostasy, the state of gravitational equilibrium between Earth's and the underlying , plays a crucial role in tectonic geomorphology by influencing vertical movements in response to changes in surface or subsurface loads. In the Airy model of , the crust "floats" on the denser mantle, and removal of overlying material—such as through —triggers isostatic rebound, whereby the crust rises to restore equilibrium. This rebound is quantified by the equation for vertical displacement Δh\Delta h: Δh=ρc⋅eρm−ρc\Delta h = \frac{\rho_c \cdot e}{\rho_m - \rho_c} where Δh\Delta h is the uplift (vertical displacement), ee is the thickness of eroded material (erosion load change), ρc\rho_c is crustal density (typically ~2700 kg/m³), and ρm\rho_m is mantle density (~3300 kg/m³), yielding a rebound factor of approximately 3–6 times the eroded thickness depending on density values. Post-glacial rebound in regions like Scandinavia exemplifies this, with ongoing uplift rates up to 10 mm/yr following ice sheet melting. Tectonic processes profoundly impact landform development by creating relief through uplift and subsidence. Convergent settings produce fold mountains, such as the Himalayas, where thrust faulting stacks crustal slices to form high plateaus and ranges exceeding 8 km in elevation. Fault-block mountains and ranges arise from extensional tectonics, as seen in the Basin and Range Province of the western United States, where alternating horsts (uplifted blocks) and grabens (subsided basins) define a characteristic topographic mosaic. Escarpments often mark the edges of uplifted blocks or fault scarps, while basins accumulate sediments in subsiding zones, influencing downstream geomorphic systems. Uplift rates driven by tectonics typically range from 1 to 10 mm/yr, varying by boundary type and location; for example, the experience localized rates up to 10 mm/yr due to focused convergence. These rates interact dynamically with surface processes, forming a tectonic denudation feedback where enhanced uplift steepens slopes and accelerates , which in turn promotes further isostatic rebound and sustains high relief. This coupling is evident in orogenic belts, where rates can match or exceed uplift, maintaining landscape disequilibrium over millions of years.

Igneous and Volcanic Processes

Igneous and volcanic processes represent key endogenic mechanisms in geomorphology, where from or lower crust ascends, intrudes into the crust, or extrudes to the surface, constructing and modifying landforms through and associated deformation. These processes create distinctive topographic features by adding material to the , often in tectonically active settings, and their products are later shaped by to reveal subsurface structures. Plutonic intrusions occur when magma cools and solidifies below the surface, forming large bodies like batholiths that can uplift and dome overlying rocks, contributing to regional relief. Volcanic eruptions, by contrast, involve the extrusion of magma as lava flows, pyroclastic deposits, or gases, rapidly building elevated landforms while influencing local and sediment dynamics. Plutonic intrusions, such as batholiths and stocks, form expansive crystalline masses that, upon exposure by erosion, create rugged terrains with granitic domes and ridges, as seen in the Sierra Nevada where the intrusion of viscous, silica-rich has domed the landscape over millions of years. These features develop through fractional in chambers, where denser minerals settle, leading to compositional that affects the resulting rock's resistance to . Dikes and sills, tabular intrusions that cut across or parallel to , respectively, act as feeder systems for surface and, when exhumed, form resistant walls or sills that control drainage patterns and in dissected terrains. For instance, the in exemplifies how intrusions can create linear cliffs exposed by river incision. Volcanic eruptions construct diverse landforms depending on magma composition and eruption style, with effusive eruptions producing broad lava plateaus and flows, while explosive events deposit pyroclastic layers that build steep cones. Shield volcanoes, characterized by low-viscosity basaltic lava flows, form gently sloping domes through repeated effusive activity, as exemplified by Mauna Loa in Hawaii, where fluid flows extend tens of kilometers. Stratovolcanoes, or composite cones, arise from alternating layers of viscous andesitic lava and pyroclastics in subduction zones, creating steep, symmetrical peaks like Mount Fuji, where gas-rich magma drives explosive phases interspersed with lahars. Cinder cones, built from fragmented scoria ejected during Strombolian eruptions, form small, steep-sided mounds, such as Paricutin in Mexico, which grew rapidly to 424 meters in height over nine years. Caldera formation occurs when a empties during cataclysmic eruptions, causing the overlying crust to collapse into a broad basin, often tens of kilometers wide, which then influences regional geomorphology through faulting and resurgence. The , formed by rhyolitic supereruptions, demonstrates this process, with post-collapse doming creating intracaldera highlands amid a subsiding depression. These structures trap sediments and alter drainage, evolving into lakes or uplands over time. The dynamics of volcanic flows are governed by magma viscosity—lower in basalts due to high temperatures and low silica, allowing extensive flows—and dissolved gas content, which propels explosive fragmentation in rhyolites. In hotspot volcanism, like the Hawaiian chain, buoyant mantle plumes generate basaltic melts independent of plate boundaries, producing voluminous shields and resulting in a chain that propagates at rates of about 0.086 meters per year as the Pacific Plate moves over the stationary plume. Subduction zone volcanism, conversely, involves hydrous melting of the mantle wedge by descending slabs, yielding viscous, gas-rich andesites that form stratovolcanoes with higher relief and frequent explosive events, as at the . Following eruptions, volcanic landforms interact with surface processes, where fresh, porous lavas and ash undergo rapid chemical weathering, accelerating and slope retreat, particularly in humid climates. The illustrate buildup rates, with the chain extending over 6,000 kilometers and individual shields like Kilauea adding volume at 0.1-1 cubic kilometer per year during active phases, though overall chain growth reflects plate motion at 7-10 centimeters annually. These interactions highlight how igneous construction sets the stage for exogenic modification, maintaining geomorphic equilibrium over millennial scales.

Exogenic Processes

Fluvial Processes

Fluvial processes encompass the interactions between flowing water in rivers and streams and the Earth's surface, primarily involving , , and deposition that shape continental landscapes. These processes are fundamental to geomorphology, as rivers redistribute vast quantities of annually, with global estimates indicating that fluvial systems transport approximately 15-20 billion tons of to the oceans each year. The driving these processes derives from the of water, modulated by channel slope and discharge, leading to dynamic adjustments in channel form and associated landforms. Erosion in fluvial systems occurs through several key mechanisms. involves the forceful impact of turbulent water flow against the channel bed and banks, dislodging and removing loose material or even large rock blocks via drag and lift forces; for instance, blocks up to 1.2 m × 1.45 m × 0.11 m have been observed being quarried from beds. Abrasion, or corrasion, results from the mechanical scraping of particles carried by the flow against the channel boundaries, producing features such as potholes, striations, and polished surfaces while progressively reducing through chipping and grinding. , also known as solution, entails the chemical dissolution of soluble rocks, such as via , which enlarges channels and creates scalloped forms on surfaces. Sediment transport in rivers distinguishes between bedload and suspended load based on particle size and flow dynamics. Bedload consists of coarser materials like sands, gravels, and boulders that move along the channel bed through rolling, sliding, or saltation (bouncing), typically comprising 5-10% of total load in gravel-bed rivers and limited by available energy. In contrast, involves finer particles such as silts, clays, and fine sands held aloft by turbulent eddies and vertical mixing, often accounting for 80-90% of the total flux in sandy or muddy rivers and governed more by sediment supply than transport capacity. Fluvial landforms arise from the interplay of and deposition, creating diverse features across the river profile. In upstream reaches, vertical incision forms V-shaped valleys with steep sides, while downstream, lateral and overbank flooding build broad floodplains—flat, sediment-rich areas periodically inundated, where fine silts and clays accumulate through vertical accretion. , sinuous bends in the channel with greater than 1.5, develop on floodplains through differential on outer concave banks and deposition on inner convex ones, migrating laterally over time; when a loop is cut off during high flow, it forms an , a crescent-shaped, isolated body that eventually infills with to create a . At confluences with standing , such as lakes or seas, reduced promotes delta formation, where coarser sediments deposit first near the mouth, building lobate or bird-foot structures as finer materials extend farther. Channel patterns reflect adjustments to sediment load, discharge variability, and slope. Braided channels feature multiple interwoven threads separated by ephemeral bars of coarse sediment, prevalent in environments with high bedload supply relative to transport capacity, such as glacial outwash plains, where flow divides around unstable gravel islands. Meandering channels, by contrast, maintain a single, winding thread with low-width-to-depth ratios, favored in cohesive floodplains with moderate sediment loads and stable banks reinforced by vegetation, allowing for smooth, helical flow that sustains the bends. The dynamics of fluvial incision and are often quantified using the equation, which estimates the energy available for geomorphic work per unit channel length: Ω=ρgQS\Omega = \rho g Q S Here, Ω\Omega represents in watts per meter (W/m), ρ\rho is the density of (approximately 1000 kg/m³), gg is (9.8 m/s²), QQ is discharge (m³/s), and SS is channel slope (dimensionless). This formulation, derived from Bagnold's work on energetics, indicates that power increases with higher discharge and steeper slopes, driving rates that can exceed 1 mm/year in steep mountain streams; for example, with Q=4Q = 4 m³/s and S=0.01S = 0.01, Ω≈392\Omega \approx 392 W/m. Unit stream power, normalized by channel width (ω=ρgQS/w\omega = \rho g Q S / w), further refines this to per-unit-bed-area values, typically ranging from 2,600 to 12,800 W/m² during floods, correlating with and entrainment thresholds. Influencing these dynamics are variations in base level—the hypothetical lower limit of , often controlled by or confluences—which, when lowered (e.g., by tectonic uplift), steepens channels upstream, enhancing incision and terrace formation. Sediment supply, modulated by upstream rates and catchment characteristics, balances with transport capacity per Lane's relation; excess supply promotes and braiding, while deficits lead to channel degradation. Human interventions, particularly , profoundly alter these factors by trapping up to 90% of incoming —global reservoirs have impounded over 5,000 km³ since 1950—reducing downstream supply, causing incision below structures (e.g., up to 3 m/year in the post-Hoover Dam), and stabilizing flow regimes that diminish flood-driven reshaping of floodplains. Climate variations indirectly affect discharge, amplifying or attenuating these processes over decadal scales.

Aeolian Processes

Aeolian processes encompass the erosion, transportation, and deposition of sediments by wind, predominantly in arid, semi-arid, and coastal environments where sparse vegetation allows wind to dominate landscape evolution. These processes are most active in regions with low precipitation and high wind speeds, such as deserts, where they redistribute vast quantities of sand and dust, forming characteristic landforms and influencing global biogeochemical cycles. Unlike water-driven exogenic processes, aeolian activity relies on turbulent airflow to mobilize loose particles, with saltation serving as the primary mode of sand transport over distances of meters to kilometers. Seminal work by Bagnold established the foundational physics of these interactions, emphasizing the role of grain size, wind velocity, and surface conditions in controlling sediment flux. Erosion in aeolian systems occurs mainly through and abrasion. removes fine, unconsolidated particles—typically and clay—directly into suspension by wind turbulence, progressively lowering the land surface and creating deflation hollows or basins, as observed in the of . Abrasion, akin to , involves wind-entrained sand grains impacting exposed rock faces at high speeds, eroding and sculpting surfaces into streamlined shapes; this mechanism is responsible for the formation of ventifacts, which are faceted pebbles and boulders with polished, pitted windward sides, commonly found in the Namib Desert. Bagnold's experiments demonstrated that abrasion rates increase with grain impact velocity and concentration, often exceeding 1 mm per year on soft rocks under sustained winds. Transportation of coarser sediments (0.06–2 mm) occurs primarily via saltation, where individual grains are lifted by turbulent eddies or impacts from preceding grains, follow arched trajectories of 10–100 cm height, and upon landing, eject additional particles in a that sustains the . This process accounts for over 50–75% of total transport in most aeolian environments, with creep—surface rolling of larger grains—contributing a minor fraction and suspension dominating for finer particles that can travel thousands of kilometers. Bagnold quantified saltation as proportional to the cube of excess above threshold, highlighting its nonlinear dependence on flow dynamics. Dune formation arises from depositional patterns during saltation, where over an initial mound decelerates on the stoss and separates at the crest, creating a low-pressure zone on the lee side that promotes accumulation and migration at rates of 10–30 m per year in active fields. The dynamics of aeolian transport hinge on the threshold velocity required to entrain grains, beyond which motion initiates and sustains. The threshold velocity u∗tu_{*t} for aerodynamic entrainment of non-cohesive grains is given by Bagnold's empirical relation: u∗t=Agd(σ−1)u_{*t} = \sqrt{A g d (\sigma - 1)}
Add your contribution
Related Hubs
User Avatar
No comments yet.