heyelan

Heyelan is the Turkish term for landslide, a mass movement of rock, soil, and sometimes water-saturated debris downslope under gravity. It includes a range of phenomena, from slow creep to rapid events such as translational slides, rotational slumps, debris flows, and rockfalls, depending on material properties and triggering conditions.

Causes include natural triggers such as heavy rainfall, snowmelt, earthquakes, and volcanic activity, as well as human factors such as deforestation, slope modification, over-steepening, poor drainage, and mining. Groundwater pressure, weak layers, and seismic shaking can reduce shear strength and initiate motion.

A landslide typically begins when a stable slope becomes unstable, often through rainfall infiltration that lubricates a slip surface, or by undercutting at the base of a slope. Movement can be rapid and destructive, generating debris flows that bury roads, buildings, and farmland, and may reroute rivers or alter drainage.

Hazard assessment relies on inventories, historical records, slope-stability analyses, and rainfall thresholds. Monitoring uses field sensors, satellite radar (InSAR), lidar, and rain gauges. Mitigation includes drainage improvements, retaining structures, rock bolts, revegetation, and land-use planning to avoid high-risk zones. Early warning systems can reduce casualties in populated areas.

In Turkey and neighboring regions, heyelan is a common geohazard in mountainous terrain and along unstable riverbanks, with activity influenced by rainfall, earthquakes, and land-use changes. Research and municipal planning map susceptibility and implement engineering measures to lessen risk.