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Landslide dam
Landslide dam
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A landslide dam or barrier lake is the natural damming of a river by some kind of landslide, such as a debris flow, rock avalanche or volcanic eruption.[1] If the damming landslide is caused by an earthquake, it may also be called a quake lake. Some landslide dams are as high as the largest existing artificial dam.[2]

Causes

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The major causes for landslide dams investigated by 1986 are landslides from excessive precipitation and earthquakes, which account for 84%. Volcanic eruptions account for a further 7% of dams.[3] Other causes of landslides account for the remaining 9%.

Consequences

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The water impounded by a landslide dam may create a dam reservoir (lake) that may last for a short time, to several thousand years.[2]

Because of their rather loose nature and absence of controlled spillway, landslide dams frequently fail catastrophically and lead to downstream flooding, often with high casualties. A common failure scenario is overflowing with subsequent dam breach and erosion by the overflow stream.[2]

Landslide dams are responsible for two types of flooding: backflooding (upstream flooding) upon creation and downstream flooding upon failure. Compared with catastrophic downflooding, relative slow backflooding typically presents little life hazard, but property damage can be substantial.

Profiles of the dam reservoir and groundwater upstream (the landslide dam is not shown in the figure)
Groundwater after dam failure downstream

While the dam is being filled, the surrounding groundwater level rises. The dam failure may trigger further catastrophic processes. As the water level rapidly drops, the uncompensated groundwater hydraulic pressure may initiate additional landslides. Those that fall into the dam reservoir may lead to further catastrophic spillages. Moreover, the resulting flood may undercut the sides of the river valley to further produce landslides downstream.[2]

After forming, the dam leads to aggradation of the valley upstream, and dam failure leads to aggradation downstream.[2]

Construction engineers responsible for design of artificial dams and other structures in river valleys must take into account the potential of such events leading to abrupt changes in river's regimen.

Coping Method

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Different coping methods might be applied according to the geographical location, environment, water storage capacity, breaching impact, coping cost, engineering difficulties and urgency .etc.

  • Continuous monitoring, evacuation
  • Excavation or blasting
  • Drainage or siphoning

Examples

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Landslide dam

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from Grokipedia
A landslide dam is a natural barrier formed when a mass movement of rock, , or completely blocks a , , or , impounding upstream to create a temporary lake. These dams typically arise in steep, narrow valleys where landslide debris spans or crosses the valley floor, often triggered by earthquakes (approximately 50% of cases), excessive rainfall or (approximately 40%), or rarely volcanic activity (8%). The resulting structure is usually heterogeneous and uncompacted, consisting of materials from rock avalanches, flows, slumps, slides, or earth flows, which distinguishes it from engineered . Landslide dams are classified into six morphological types based on their interaction with the valley: Type I (11%) involves small blockages that do not fully span the valley; Type II (44%) spans the valley floor directly; Type III (41%) features debris that moves upstream or downstream along the valley; while Types IV–VI are rarer and involve more complex configurations like complete burial of the valley or plug-like blockages. Their stability is generally low due to poor sorting of materials, lack of consolidation, and high seepage potential, with approximately 85% failing within of formation. Factors influencing include dam , , foundation permeability, and the rate of upstream water inflow, but most persist only days to months. The primary risks associated with landslide dams stem from their frequent and rapid failure, which can unleash catastrophic downstream flooding through overtopping (the most common mode), internal erosion (piping), or slope instability. Of 73 documented failures, 27% occurred within one day and 50% within 10 days, often amplifying flood peaks far beyond natural river flows and causing widespread destruction. Upstream, the impounded lakes can flood settlements or ecosystems, while dam breaches have historically led to high fatalities; for instance, the 1933 Diexi dam in triggered floods that killed 2,423 people. Notable examples include the 1911 Usoy dam in the (largest known, with a 2 km³ lake volume, formed by a 2 billion m³ earthquake-induced , persisting for over a century without ) and the 1959 Madison Canyon in , (a 20 million m³ earthquake-induced event that caused 28 deaths by burying campers and formed a dam that was stabilized without ). These events highlight the dual role of dams in geomorphic —temporarily altering profiles and dynamics—while posing significant hazards in mountainous regions worldwide.

Definition and Formation

Definition

A is a formed when massive volumes of debris from a , such as rockfalls, soil slumps, debris , or earth flows, completely obstruct a river valley or channel, impounding water upstream to create a or lake. These formations arise primarily in mountainous regions with steep slopes and narrow valleys, where mass movements can rapidly redirect fluvial systems. Unlike engineered artificial dams, which incorporate structured materials, spillways, and outlets for controlled water release, landslide dams are inherently unstable due to their loose, heterogeneous composition of unconsolidated rock, , and , rendering them highly porous and prone to seepage without any designed drainage mechanisms. When triggered by seismic activity, such dams are sometimes termed "quake lakes," highlighting their association with earthquake-induced . In terms of scale, certain landslide dams attain heights exceeding 100 meters—comparable to many of the world's tallest artificial structures—but feature irregular geometries and variable material densities that contrast with the uniform engineering of man-made barriers. If sufficiently stable, some landslide dams can endure for thousands of years, trapping sediments and forming extensive paleolakes that preserve geological records of ancient environmental conditions.

Formation Processes

Landslide dams form through a rapid sequence of geomorphic and hydrological processes initiated by the of slope material into a river valley. The process begins with the initiation of a , where unstable slope material—such as rock, , or —is dislodged and mobilized downslope, often traveling at high velocities due to gravitational forces and reduced . This mobilization generates a large volume of , typically ranging from 10^6 to 10^9 cubic meters for significant dams, which is carried by or entrained into the valley floor. Upon reaching the river channel, the undergoes rapid deposition, forming a barrier that blocks the natural flow of the watercourse. The efficiency of this blockage depends on the valley's morphology, including its narrow width and confinement, which helps concentrate the into a cohesive spanning the channel. A steeper river gradient can increase the inflow , promoting quick accumulation and sealing of the riverbed, while the 's heterogeneous composition allows initial blockage despite high permeability that facilitates seepage. Hydrological dynamics play a critical role here, as the incoming river flow interacts with the settling , potentially incorporating and enhancing the dam's height and width to fully obstruct the . With the channel blocked, water begins to impound upstream, leading to the formation of a reservoir as inflow accumulates behind the debris barrier. This impoundment phase involves rising water levels that exert hydrostatic pressure on the dam, causing initial seepage through permeable zones in the debris matrix. In some cases, early overtopping occurs if the reservoir fills rapidly and surpasses the dam crest, initiating surface erosion. The overall formation is often instantaneous, occurring over minutes to hours for the initial blockage, though the reservoir may build more gradually over days to weeks depending on inflow rates and dam geometry. Recent examples include the 2024 Chilcotin River landslide dam in Canada and the 2025 Matai'an landslide dam in Taiwan (as of November 2025), demonstrating continued occurrence of these processes. Cross-sectional profiles of landslide dams, as illustrated in schematic diagrams, typically show a heterogeneous debris barrier with a central core flanked by side deposits, overlain by the accumulating reservoir water body.

Causes

Natural Triggers

Natural triggers for landslide dams primarily involve geological and climatic processes that destabilize slopes and mobilize large volumes of debris into river valleys. Among these, earthquakes and excessive precipitation stand out as the most frequent initiators, with seismic activity causing intense ground shaking that dislodges rock and soil masses, while heavy rainfall saturates slopes, reducing and promoting failure. According to a comprehensive of 1,393 documented landslide dams worldwide, earthquakes account for 50.5% of cases, and rainfall for 39.3%, together comprising nearly 90% of all natural triggers. This updates earlier assessments, such as Schuster and Costa's 1987 compilation, which identified rainfall/ and earthquakes as responsible for 90% of cases based on fewer records. Other natural factors, though less common, include volcanic eruptions, rapid snowmelt, and glacial outbursts, which can contribute to debris mobilization and dam formation. Volcanic activity, often through lahars or sector collapses, triggers approximately 0.9% of landslide dams, while accounts for 2.4%. Glacial lake outburst floods (GLOFs) or ice-dammed failures can exacerbate slope instability in high-altitude regions by rapidly increasing water loads and eroding underlying materials. The following table summarizes key trigger percentages from the global dataset:
Trigger TypePercentageApproximate Cases (out of 1,393)
Earthquakes50.5%704
Rainfall39.3%548
2.4%33
Volcanic Activity0.9%13
Unknown4.7%66
These proportions highlight the dominance of seismic and hydrometeorological events in dam formation. Landslide dams exhibit distinct regional patterns, with higher incidences in tectonically active and seismically prone zones such as the , , , and the , where frequent earthquakes intersect with steep and fragile geology. In these areas, the combination of active plate boundaries and monsoon-influenced climates amplifies the risk, as evidenced by clusters of dams in global inventories like the RAGLAD database, which documents over 700 cases predominantly in mountainous terrains. Human influences, such as , can exacerbate these natural triggers by weakening slopes, though they are addressed separately.

Human Influences

Human activities play a pivotal role in exacerbating the formation of landslide dams by destabilizing slopes and amplifying natural triggers through landscape modification. Deforestation and broader land-use changes, such as conversion to agriculture or urban development, remove root systems that anchor soil and regulate water infiltration, thereby increasing slope instability and the likelihood of mass movements during intense rainfall. These alterations can lead to larger-scale landslides capable of blocking river valleys, forming temporary dams that pose flood risks. Mining and quarrying operations further contribute by excavating valley walls and disrupting subsurface , which weakens geological structures and promotes failure. Similarly, road construction in rugged terrains often involves undercutting and inadequate drainage, creating preferential failure planes that facilitate flows or slides into waterways. These human-induced modifications contrast with purely natural processes by introducing modifiable vulnerabilities that accelerate formation in susceptible areas. Anthropogenic climate change intensifies these risks by altering patterns, with global warming leading to more frequent and severe rainfall events that trigger . In High Mountain Asia, for example, landslide activity is projected to increase by 30–70% by 2061–2100, particularly in monsoon-affected zones near glacial lakes, due to heightened extreme exceeding 20 mm/day. Under moderate emissions scenarios, global annual landslide casualties could rise by approximately 150% to around 8,000 by 2066–2095, underscoring the amplified threat to dam-prone regions. Rapid in developing regions has driven a notable uptick in dam incidents, as expanding built environments encroach on unstable slopes and heighten sensitivity to rain-induced failures. Urban areas exhibit up to 10 times greater vulnerability to precipitation-triggered s than rural counterparts, a trend persisting for decades post-development due to lasting topographic and vegetative disruptions. This pattern is evident in studies from the early , where human alterations account for disproportionate risks in densely populated mountain belts. Neglecting geohazards during infrastructure compounds these issues, resulting in elevated rates of dam formation and associated damages. Without integrating hazard assessments, such as susceptibility maps, projects like reservoirs or highways become hotspots for failures, leading to , reduced operational lifespan, and economic losses exceeding billions annually worldwide. Proper foresight in could mitigate these avoidable escalations by prioritizing sites and .

Characteristics

Physical Properties

Landslide dams consist of a heterogeneous mixture of unconsolidated , including boulders, , fragmented rock, and often entrained , which can be broadly classified into soil-type (predominantly fine materials), debris-type (mixed coarse and fine particles, the most common), and rock-type (larger blocks with higher stability). This composition results in a loose, poorly sorted structure with bimodal or wide distributions spanning several orders of magnitude, from fine to meter-scale boulders. The materials exhibit high , typically in the range of 20-50%, which promotes seepage and contributes to internal instability. Geometrically, landslide dams display significant variability in dimensions, with heights ranging from 5 m to over 250 m, lengths from 100 m to 10 km, and crest widths that can span hundreds of meters but often remain narrow relative to the valley floor. Their profiles are typically irregular and trapezoidal or triangular, shaped by the dynamics of the deposition, and they frequently lack a defined , leading to uncontrolled overflow during filling. These features result in capacities that can reach billions of cubic meters, as seen in cases like the Attabad dam, which impounded approximately 0.4 km³ of . The hydrological properties of landslide dams are dominated by their high permeability, arising from the coarse, unconsolidated materials, which facilitates seepage flows and can initiate through internal erosion when hydraulic gradients exceed critical thresholds. Permeability values can vary widely, spanning orders of magnitude (e.g., 10^{-9} to 10^{-7} m²), depending on distribution and packing , with coarser promoting faster seepage. In comparison to artificial dams, landslide dams are uncompacted and unreinforced, yielding lower overall due to their loose structure and minimal cementation. is often modeled using the Mohr-Coulomb criterion: τ=c+σtan⁡ϕ\tau = c + \sigma \tan \phi where τ\tau is the , cc is cohesion (typically 0-10 kPa for these materials), σ\sigma is the effective normal stress, and ϕ\phi is the friction angle (around 30-40°). This low cohesion reflects the frictional dominance in unconsolidated debris, contrasting with the higher engineered strengths in constructed embankments.

Types of Landslide Dams

Landslide dams are classified primarily based on the composition and formation mechanism of the impounding , which influences their , stability, and longevity. The main types include dams, formed by coherent masses of fractured rock from steep cliffs or slopes; dams, consisting of loose, saturated mixtures of , rock fragments, and water; earthslide dams, dominated by displaced and ; and volcanic dams, resulting from lahars (volcanic mudflows) or pyroclastic debris . These categories reflect the dominant mass-wasting processes, such as slides, flows, or , that deliver to block river valleys. Sub-classifications further distinguish dams by their geometric relation to the valley and duration. Dams can form complete blockages that span the entire valley floor or partial damming where material only partially obstructs flow, categorized into types I through VI based on valley interaction, with Type II (full span) being most common at about 44% of documented cases. Regarding persistence, temporary dams typically last days to months due to rapid or overtopping, while persistent ones endure for centuries to millennia, often through natural cementation or stabilization. Formation-specific traits highlight differences in stability: rockslide dams tend to be more resilient owing to interlocking rock fragments that resist seepage and erosion, whereas debris flow dams, with their unconsolidated and permeable material, are prone to quick failure via piping or surface overflow. Earthslide dams exhibit intermediate stability, depending on soil cohesion, while volcanic dams vary widely based on hot pyroclastic content, which can initially enhance impermeability but lead to later instability from remobilization. These properties link directly to the physical characteristics of the dam material, such as grain size and permeability, as outlined in prior sections on physical properties. Globally, landslide dams are concentrated in tectonically active regions like the , , and Alpine belts, with debris flow types predominant in humid, precipitation-prone areas where intense rainfall mobilizes loose sediments. A database of over 400 significant dams since 1900 indicates that rock and debris types comprise the majority, reflecting their prevalence in mountainous terrains susceptible to seismic and climatic triggers.

Stability and Failure

Factors Affecting Stability

The stability of landslide dams is influenced by a combination of internal material properties and external environmental forces, which collectively determine their resistance to , seepage, and structural . Internal factors primarily relate to the composition and mechanical characteristics of the dam material. The strength of the dam body, often derived from the landslide , varies significantly; rock-dominated dams exhibit greater stability due to higher compared to or types, which comprise loose, heterogeneous materials prone to deformation. A key parameter is the internal friction angle of the materials, typically ranging from 20° to 40° for common and mixtures in landslide dams, which governs shear resistance along potential planes; lower angles in fine-grained soils reduce overall stability. The degree of consolidation affects and load-bearing capacity, with poorly consolidated dams experiencing higher settlement under reservoir loading, while well-consolidated ones better withstand stresses. Internal potential, particularly in gap-graded sediments, further compromises integrity by progressively removing finer particles and creating voids that propagate instability. External factors accelerate destabilization by imposing dynamic loads on the dam structure. Rapid level rise behind the dam increases hydrostatic pressure, reducing within the dam body and promoting seepage forces that can lead to progressive failure. Seismic aftershocks, common in tectonically active regions where many dams form, induce vibrations that cause cracking, settlement, and in saturated zones, significantly lowering stability. Wave action from upstream inflows or landslides generates surges that erode the dam crest and upstream face, narrowing the structure and heightening overtopping risk. Additionally, rainfall infiltration elevates , decreases , and enhances internal , with rainfall-triggered dams showing instability rates up to 67%. Stability assessments often employ empirical indices that integrate geometric and hydromorphological parameters to predict and potential. More comprehensive tools, like the Hydromorphological Dam Stability Index (HDSI = log(V_L / (A_b × S)), where V_L is landslide volume (m³), A_b is upstream (km²), and S is channel (m/m)), classify dams into stability domains based on thresholds (e.g., HDSI > 7.44 for ), aiding rapid post-formation evaluation. Global inventories indicate that approximately half of landslide dams within ten days of formation, underscoring their transient nature. About 15% persist beyond one year, with a few enduring over 100 years due to favorable geometry and minimal external loading.

Breaching Mechanisms

Landslide dams can fail through several primary breaching mechanisms, each governed by the interplay of hydraulic, geotechnical, and external forces acting on the dam's heterogeneous structure. The most common is overtopping, where water exceeds the dam crest, initiating surface that progressively widens and deepens the breach. This process begins with turbulent flow scouring the downstream face, forming a headcut that migrates upstream, leading to rapid dam dismantling. Another mechanism is piping or seepage, involving internal where high hydraulic gradients drive fine particles through the body, creating subsurface channels or "pipes" that enlarge over time and culminate in sudden collapse if unchecked. Liquefaction, often triggered by seismic loads, occurs when saturated materials lose due to elevated pore pressures, transforming the structure into a fluid-like state that flows and fails abruptly. Finally, sliding involves large-scale slope failure, typically on the downstream face, where buoyant forces from rising water reduce below the material's resistance, causing translational movement along a weak plane. The physics of breaching emphasizes erosive and hydrodynamic processes, with overtopping discharges often modeled using a weir flow equation to estimate initial outflow: Q=C⋅L⋅H3/2Q = C \cdot L \cdot H^{3/2} where QQ is the discharge (m³/s), CC is the (typically 0.4–0.6 for rough crests), LL is the breach length (m), and HH is the water head above the crest (m). Breach propagation speeds range from 1 to 10 m/min, influenced by sediment erodibility and flow , while peak discharges can reach 10⁴ to 10⁶ m³/s in large events, amplifying downstream hazards. These dynamics highlight the non-uniform nature of landslide dam materials, which include coarse blocks and fines, leading to variable rates compared to homogeneous earthen dams. Failure timelines vary by mechanism: overtopping and sliding often progress in hours to days from initial incision to full breach, while may extend over days to weeks before accelerating. Approximately 50% of documented dam breaches occur catastrophically, releasing impounded and in a short burst. Post-failure, the process involves substantial release from the former and dam body, followed by channel incision that reshapes the valley floor and can trigger secondary erosion upstream and downstream.

Impacts and Consequences

Upstream Effects

The formation of a reservoir behind a landslide dam leads to upstream flooding and inundation as water accumulates in the blocked valley, submerging land and altering local landscapes. This process can occur rapidly, with lakes filling in hours to months depending on inflow rates and dam geometry; for instance, the 2010 Attabad landslide in created Hunza Lake, which inundated 5 villages, 240 houses, and 25 km of the within 5 months, displacing local communities and disrupting access. In larger cases, such as the 1911 Usoi landslide in that formed Lake Sarez with a volume of 17 km³, the impoundment submerged extensive upstream areas, including valleys and settlements, over decades. These inundations also cause habitat loss for aquatic and riparian species, as submerged ecosystems transition to lacustrine environments, reducing in affected river reaches. Sedimentation in the upstream traps incoming s from the river, leading to and changes in and nutrient cycles. Landslide dams act as effective sediment sinks, with fluvial deltas and lacustrine deposits accumulating behind the barrier; the 1933 Diexi landslide dam in , for example, resulted in up to 240 m of sediment thickness in its impoundment before breaching. This trapping reduces downstream sediment supply while altering upstream flow dynamics, potentially promoting finer-grained deposition that affects and aquatic habitats by burying and disrupting nutrient transport. Over time, such sedimentation can fill smaller reservoirs, extending the impoundment upstream and modifying valley floor . The rising reservoir levels behind landslide dams elevate local groundwater tables, causing soil saturation in adjacent slopes and increasing the risk of secondary landslides. This saturation weakens slope stability by reducing shear strength and pore pressure buildup, as observed in reservoir-induced landslides where water infiltration exacerbates existing instabilities; analogous effects occur in landslide dam impoundments, where prolonged submersion has triggered additional mass movements upstream. Such changes can propagate hazards, with saturated soils leading to further blockages or erosion in the valley. Socioeconomic impacts from upstream reservoir formation include temporary relocation of populations and economic losses from inundated land, particularly in populated valleys. In the case of Hunza Lake, the flooding displaced residents from 5 submerged villages, affecting hundreds of people and requiring resettlement with costs for infrastructure repair exceeding millions in local currency. For larger events like the 2008 Tangjiashan landslide dam in , upstream inundation and associated risks prompted evacuations and relocations impacting approximately 200,000 individuals in the broader affected region, alongside losses from submerged farmland and housing valued in the tens of millions of USD. These disruptions often involve community displacement, loss of , and temporary until stabilization or breaching occurs.

Downstream Effects

The failure of a landslide dam often results in the sudden release of impounded , generating a powerful wave that propagates downstream as a debris-laden . These floods carry , boulders, and woody , amplifying their destructive force and enabling distances of up to 100-500 km or more, as observed in historical cases where waves traveled over 550 km while retaining heights of 16.5 m. The propagation dynamics are influenced by channel geometry and load, leading to rapid attenuation in wider sections but sustained high velocities in confined reaches. Such outburst floods pose severe damage potential to downstream areas, devastating like bridges, roads, and railroads, while inundating agricultural fields and settlements. Historical document destruction of villages, farms, and urban fringes, with economic losses extending to thousands of hectares of farmland. Death tolls from these events can reach up to 100,000, as in the catastrophic following the 1786 Dadu River in , highlighting the human vulnerability in densely populated valleys. Environmentally, these floods induce significant fallout through intense riverbed scouring, where depths can exceed 50 m near the breach site, reshaping valleys over decades. Ecosystem disruption occurs via burial of habitats under thick deposits and alteration of aquatic communities, while long-term channel widening—often by tens of meters—promotes and shifts in , affecting and far downstream. Risks are amplified in narrow valleys, where confinement accelerates flow velocities and concentrates erosive power, exacerbating impacts on linear settlements. Peak discharges during breaching can surge to 10-100 times the normal river flow, for instance reaching 50 times the annual maximum in confined Andean rivers, overwhelming natural and built defenses.

Historical and Notable Examples

Ancient Examples

In the Himalayan region, tectonic activity has triggered numerous prehistoric landslide dams from large rock avalanches and debris flows, some persisting for over years due to natural cementation processes that enhanced their stability. For instance, the Diexi landslide dam in the Minjiang River valley, eastern (adjacent to the ), blocked the river around 25,000–20,000 years ago, forming a paleolake that endured for more than years before partial breaching. Evidence derives from sedimentary records of upstream lacustrine clays and silts interlayered with landslide debris, downstream outburst flood gravels, and paleoshoreline terraces preserved along valley slopes, dated via optically stimulated luminescence (OSL) on quartz grains and radiocarbon analysis of organic matter in shear zones, revealing episodic stability punctuated by minor overflows. Similarly, in the upper River's Jishi Gorge, multiple ancient landslides around 8,100 calibrated years (cal yr ) created temporary dams, impounding lakes evidenced by thick sequences of dammed-lake sediments and flood deposits that buried prehistoric settlements, with stability aided by carbonate cementation binding the debris matrix. These ancient dams played a pivotal role in landscape evolution, diverting river courses, promoting of fine-grained s upstream, and triggering downstream incision and boulder-strewn floodplains upon breaching, as seen in the scoured gorges and alluvial fans of the . Unlike many short-lived modern dams composed of loose talus, prehistoric examples often achieved long-term stability through diagenetic processes like and infilling, which cemented fractures and reduced permeability, allowing some structures to withstand tectonic stresses for . Such durability is documented in Himalayan cases where recemented breccias and colluvial fills resisted , contrasting with the rapid failure typical of uncemented contemporary events.

Modern Examples

One prominent modern example of a landslide dam occurred during the 2008 Wenchuan earthquake in , where the Tangjiashan dam formed on May 25, 2008, following a massive triggered by the Mw 7.9 seismic event that blocked the Jianjiang River. The dam, composed of approximately 20 million cubic meters of debris and standing about 105 meters high, impounded a with a capacity of roughly 315 million cubic meters, posing a severe risk to downstream areas including the city of . In response, Chinese authorities conducted a controlled breaching on June 10, 2008, by excavating spillways and using explosives, which successfully drained the lake without loss of life from the dam failure; however, preparations included evacuating over 250,000 people and planning for up to 1.3 million in potential flood zones. In February 2021, a catastrophic rock-ice in India's , , generated a temporary landslide dam along the Rishiganga River. The event on February 7, 2021, involved about 27 million cubic meters of material dislodged from near Ronti Peak, creating a debris blockage approximately 40 meters thick at the confluence with the Ronti Gad stream, which rapidly impounded water before breaching and causing a . This failure destroyed the Rishiganga and Tapovan-Vishnugad projects, resulting in over 200 fatalities or missing persons and widespread damage. The 2024 Hualien earthquake in also produced several landslide dams, highlighting ongoing seismic risks in tectonically active regions. On April 3, 2024, the Mw 7.4 event triggered over 1,200 landslides across eastern , including four notable valley-blocking dams, one of which formed a 700-meter-long lake behind a in the Hualien area near a hydropower station. These dams were closely monitored using real-time seismic networks and , with no major breaches reported, allowing for timely assessments and minimal additional impacts beyond the earthquake's initial 21 fatalities. On July 30, 2024, a large in , , blocked the Chilcotin River in Farwell Canyon, forming a natural approximately 1,000 meters long, 600 meters wide, and 30 meters deep, with an estimated debris volume of 18 million cubic meters. The blockage impounded a lake that grew to threaten downstream communities along the , prompting evacuations and monitoring by authorities. The dam breached naturally on August 5–6, 2024, releasing a surge of water that caused flooding but no fatalities, while impacting and local ecosystems. In 2025, the Matai'an rock in led to multiple landslide dam formations and breaches. Initial debris from the avalanche created barrier lakes that breached in September 2025, generating that killed at least 15 people. A subsequent barrier lake formed and breached on October 21, 2025, producing another damaging , but no fatalities occurred due to successful evacuations of downstream populations. These events underscored the risks of recurrent damming in seismically active areas with heavy rainfall. Since 2010, documentation of landslide dams has increased significantly, with over 20 events recorded globally, many linked to intensified extremes such as heavy rainfall and rapid glacier melt exacerbating slope instability. Satellite systems like Landsat and have enabled this enhanced tracking, as seen in monitoring the evolution of multiple dams from the 2016 Kaikōura earthquake in , where time-series imagery revealed lake formation and drainage patterns. These trends reflect broader patterns of rising landslide frequency due to global warming, with studies projecting continued increases in dam-forming events in vulnerable mountainous regions. Modern responses to landslide dams have demonstrated improved outcomes through faster detection and intervention, substantially reducing fatalities compared to historical cases. For instance, the proactive evacuation and engineering at Tangjiashan averted a potential that could have affected millions, while advancements in and early warning systems in events like the 2024 Hualien quake, Chilcotin River blockage, and 2025 Matai'an breaches have minimized secondary flood risks. Overall, these efforts have lowered death tolls in documented 21st-century incidents, emphasizing the value of integrated monitoring technologies in hazard management.

Monitoring and Mitigation

Detection Methods

Detection of landslide dams relies on a combination of and ground-based techniques to identify sudden blockages in river valleys caused by s, enabling timely assessment of potential hazards. methods provide broad coverage, particularly useful in inaccessible regions, by capturing changes in landscape and water features post-event. , such as that from the mission, facilitates the detection of landslide-dammed lakes through multispectral analysis of water bodies and debris deposits, allowing for automated mapping of dam formations over large areas. (Light Detection and Ranging) technology excels in quantifying topographic alterations, such as valley infilling and elevation changes, by generating high-resolution digital elevation models that reveal dam structures with centimeter-level precision. Unmanned aerial vehicles (UAVs or drones) offer real-time surveys in the immediate aftermath, equipped with cameras or to produce orthomosaics and 3D models for assessing dam extent and stability in dynamic environments. Ground-based methods complement by providing precise, localized data on precursors and ongoing processes. Seismometers detect precursor tremors and seismic signals generated by movement and formation, enabling rapid identification of events through of ground vibrations. Hydrological gauges measure unnatural rises in lake levels or changes in river discharge upstream and downstream, signaling impoundment and aiding in volume estimation. Early warning systems integrate these data sources to predict formation risks. For instance, USGS alert systems issue warnings in high-risk zones. Recent advances include models for stability prediction, achieving improved forecasting as of 2025. These models enhance response times but require validation against real-time observations. Challenges in detection arise primarily from remote terrains, where limited access and hinder optical , often restricting the effective detection window to hours for seismic methods and up to days for revisits. Integrating multi-sensor can mitigate these issues, informing subsequent strategies.

Management Strategies

Management strategies for dams integrate non-structural and structural measures to mitigate risks of breaching and flooding, prioritizing human safety and protection. These approaches are informed by stability assessments and aim to enable controlled release while minimizing environmental impacts. Non-structural measures emphasize and reduction without altering the dam physically. Evacuation identifies vulnerable populations in upstream inundation zones and downstream paths, establishing clear protocols, assembly points, and transportation to facilitate rapid relocation during threats. Public alerts rely on early warning systems that disseminate real-time information via sirens, , and media to prompt immediate action and reduce casualties. zoning employs hydraulic breach models to map flood-prone areas, guiding land-use restrictions, requirements, and development prohibitions to limit exposure in high-hazard regions. Structural interventions focus on solutions to manage impounded and enhance stability. Excavation of spillways involves removing to create controlled overflow channels, allowing gradual discharge and preventing overtopping, as applied successfully in restoring river flow after seismic events. Controlled blasting targets weak sections to initiate safe breaches under monitored conditions, accelerating failure in a predictable manner when natural stability is low. Tunneling constructs drainage passages through the body or abutments for sustained outflow, often serving as a permanent remedy in larger blockages. Siphons provide temporary drainage by harnessing to siphon water over or through the dam crest, to lower lake levels without excavation. Pumped diversion uses mechanical pumps to redirect inflow upstream or to channels, averting rapid accumulation during high-rainfall periods. Advanced techniques build on these foundations for complex scenarios. Pumped diversions can integrate with remote monitoring for automated operation, while —such as geotextiles and meshes—bolster dam flanks against and seepage, enhancing overall integrity. These methods have helped avert uncontrolled failures by reducing peak discharge risks, as evidenced in cases where diversions curtailed flows below critical thresholds. New monitoring instruments for dynamic safety evaluation have been developed as of 2023. Policy frameworks provide overarching guidance, with emphases on aligned with the Sendai Framework for , incorporating projections of intensified precipitation and seismic activity into adaptive planning, promoting multi-hazard integration and community-based resilience building.

References

  1. https://www.usgs.gov/glossary/landslides-glossary
  2. https://pubs.usgs.gov/of/1987/0392/report.pdf
  3. https://www.frontiersin.org/articles/10.3389/feart.2021.659935/full
  4. https://www.usgs.gov/publications/formation-and-failure-natural-dams-0
  5. https://www.undrr.org/publication/usoi-landslide-dam-and-lake-sarez-assessment-hazard-and-risk-pamir-mountains-tajikistan
  6. https://www.usgs.gov/observatories/yvo/news/1959-madison-slide-part-1-a-deadly-consequence-hebgen-lake-earthquake
  7. https://pubs.geoscienceworld.org/gsa/gsabulletin/article/100/7/1054/182167/The-formation-and-failure-of-natural-dams
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