Landslides kill an estimated 4,600 people per year globally and cause billions of dollars in infrastructure damage. The interactive explorer below visualizes nearly 13,000 recorded events across 156 countries, according to the United States Geological Survey (USGS). As extreme rainfall intensifies and development expands into hillside terrain, understanding landslide causes is critical for protecting communities and infrastructure.
Landslide causes fall into two categories: the conditions that make slopes unstable and the triggers that set them in motion. Rainfall is the most common trigger, but the underlying causes include slope angle, soil composition, vegetation loss, and human activity. As one of the 12 physical risk hazards in climate risk assessment, landslide risk combines precipitation intensity with terrain analysis to identify where slopes are most likely to fail.
What Causes Landslides?
Landslide causes include both preparatory factors that weaken slopes over time and triggering events that initiate movement. Most landslides result from a combination of multiple causes rather than a single factor.
Intense or prolonged rainfall. Water is the most common landslide trigger. Rainfall saturates soil, increases pore water pressure, and reduces the friction that holds slopes in place. A single day of extreme rainfall can trigger hundreds of landslides across a mountainous region. Regions experiencing increases in rainfall intensity face growing landslide risk even on slopes that have been stable for decades.
Steep slopes. Gravity is the driving force behind all landslides. Steeper slopes concentrate gravitational stress on soil and rock layers. Slopes above 15° are significantly more susceptible, and slopes above 30° face high landslide risk even under moderate rainfall. Slope angle is the strongest predictor of landslide causes in risk assessment models.
Soil and rock composition. Weak geological materials, including clay-rich soils, weathered rock, and unconsolidated sediment, are more prone to failure. Layers of permeable material sitting above impermeable bedrock create slip planes where water accumulates and reduces cohesion.
Vegetation removal. Tree and shrub roots stabilize slopes by binding soil and absorbing water. Deforestation, wildfire, and land clearing remove this natural reinforcement, dramatically increasing landslide causes. Studies from the Food and Agriculture Organization (FAO) show that deforested hillsides are up to 10 times more susceptible to shallow landslides.
Human activity. Road construction, mining, and building on slopes alter natural drainage patterns and remove material that supports hillsides. These human-caused modifications rank among the leading landslide causes in developing regions where construction regulations are limited.
Types of Landslides
Landslides vary in speed, material, and mechanism. The four main types reflect different landslide causes and conditions:
Slides. Blocks of soil or rock move along a defined slip surface. Rotational slides curve along a concave surface, while translational slides move along a flat plane. Slides are the most common type in mountainous terrain with layered geology.
Flows. Saturated soil and debris move as a fluid mass. Mudflows and debris flows travel at high speed, carrying boulders, trees, and sediment. Flows are typically triggered by intense rainfall on steep, saturated slopes and rank among the most destructive landslide types.
Falls. Rock or soil detaches from a steep slope and falls through the air. Rockfalls are common on cliff faces and road cuts where weathering loosens material. Falls happen rapidly with little warning.
Spreads. Lateral spreading occurs when a stable upper layer moves over a weaker, liquefied lower layer. Spreads are often triggered by earthquakes but can also result from erosion undermining the base of a slope.
Explore Global Landslide Events
The landslide causes described above have contributed to over 12,948 recorded events across 156 countries. The interactive map below, powered by NASA’s Cooperative Open Online Landslide Repository (COOLR), visualizes two decades of landslide data. Use the category filters to explore different landslide types, or drag the timeline slider to focus on specific years.
South and Southeast Asia account for the highest event density, driven by the combination of steep terrain, monsoon rainfall, and deforestation on hillsides. These are the same landslide causes identified above, converging in regions where population growth pushes development into high-risk slopes. For the full-page version with detailed country data, visit the Landslide Risk Map tool.
How Is Landslide Risk Assessed?
Landslide risk assessment combines NASA NEX-GDDP-CMIP6 precipitation data with NASA SRTM elevation and slope analysis. The methodology calculates a landslide susceptibility score by multiplying maximum daily precipitation by a slope factor that reflects landslide causes related to terrain:
| Terrain Type | Slope | Slope Factor | Landslide Risk |
|---|---|---|---|
| Flat | Less than 2° | 0.0 | Always Low (no slope) |
| Moderate slope | 2-5° | 0.5 | Risk only with extreme rainfall |
| Steep slope | 5-15° | 1.0 | Significant susceptibility |
| Very steep | Greater than 15° | 2.0 | High susceptibility, debris flow risk |
The resulting landslide susceptibility score is rated on a 5-tier scale:
| Risk Rating | Susceptibility Score | Interpretation |
|---|---|---|
| Low | Less than 30 | Minimal slope failure potential |
| Moderate | 30-80 | Possible under extreme conditions |
| High | 80-150 | Likely during intense rainfall events |
| Severe | 150-250 | Frequent slope failures expected |
| Extreme | Greater than 250 | Chronic instability, high debris flow risk |
Flat terrain always receives a Low risk rating regardless of rainfall, since slope is the primary enabling condition for landslides. Platforms like Continuuiti assess landslide risk alongside 11 other climate hazards for a complete physical risk profile.
Landslide Prevention and Mitigation
Preventing landslides focuses on addressing the landslide causes that can be controlled: drainage, slope reinforcement, and land use management.
Drainage management. Redirecting surface water and groundwater away from vulnerable slopes reduces the water pressure that triggers most landslides. Drainage systems, retention walls, and grading are the most effective interventions for slopes with known instability.
Slope reinforcement. Retaining walls, soil nailing, and geotextiles stabilize slopes by providing mechanical support. Vegetation planting restores the root networks that naturally reinforce slope stability.
Land use planning. Avoiding construction on steep, unstable slopes is the most cost-effective landslide prevention measure. Hazard mapping identifies high-risk zones where development should be restricted or require engineered mitigation.
Early warning systems. Rainfall-triggered landslide warning systems monitor precipitation thresholds and soil moisture to issue alerts before slope failure. These systems are particularly effective for protecting transportation corridors and settlements in mountainous regions.
Frequently Asked Questions
What are the main causes of landslides?
The main landslide causes are intense or prolonged rainfall, steep slopes, weak soil or rock composition, vegetation removal, and human activity such as road construction and mining. Most landslides result from a combination of multiple causes rather than a single factor.
What are the types of landslides?
The four main types are slides (movement along a defined slip surface), flows (saturated debris moving as a fluid mass), falls (rock detaching from steep slopes), and spreads (lateral movement over a weaker lower layer). Flows are typically the most destructive.
How is landslide risk assessed?
Landslide risk assessment combines NASA NEX-GDDP-CMIP6 precipitation data with NASA SRTM slope analysis. Maximum daily precipitation is multiplied by a slope factor to produce a susceptibility score rated from Low to Extreme. Flat terrain always receives Low risk regardless of rainfall.
How does climate change affect landslide risk?
Climate change intensifies extreme rainfall events that trigger slope failures. Regions with rising rainfall intensity face growing landslide causes even on previously stable slopes. Increased wildfire frequency also removes slope-stabilizing vegetation, compounding the risk.
Landslide causes are well understood but their interaction with climate change creates new risk in regions that were historically stable. As extreme precipitation intensifies and land use changes accelerate, landslide risk screening that combines rainfall projections with terrain analysis identifies where slope failures are becoming more likely.
