Mass Movement

Sentinel-1 radar coverage from before and after the 1 April 2017 mudslide in Mocoa, Colombia. Triggered by heavy rain, the landslide caused greatest movement (red) on top of a mountain. It then pushed mud down across the city of Mocoa (green) and crossed the nearby river. The Sentinel-1-derived data product (from scans on 20 March and 1 April) has been overlaid onto a Sentinel-1 radar image. Image: Modified Copernicus Sentinel data (2017), processed by I. Parcharidis, Harokopio University of Athens.

Definition

Mass movements can be defined as as any type of downslope movement of earth materials, such as sediment, soil and rock material. Mass movements are processes of erosion, transport and accumulation of material that occur on both gentle and steep slopes mainly owing to gravitational forces (IRDR Glossary).

These movements are generally associated with other disasters such as earthquakes, floods, thunderstorms and heavy rainstorm. They can be also associated with manmade hazards like construction roads, buildings, structures, infrastructure facilities.

 

Facts and figures

Mass movements occur based on several factors and causes differ depending on different regions. Mass movements are affected by the slope gradient, climate, rock type and structure, physical setting and geological and geomorphological outlines (Advances in Geosciences).

Mass-wasting events come in many shapes, sizes and speeds. Typically, the steeper the angle of a slope, the faster will be the down-slope movement of rock and sediment.  Also, water can play a significant role in mass wasting, sometimes acting as the key component to a mass-wasting event, or serving as a lubricant within a mass of sediment and rock, enabling it to travel faster and further than it would otherwise.

 

One type of mass wasting can evolve into another type of mass wasting as the body of sediment/rock moves down a slope. This can make it difficult to classify a single event as being one type of mass wasting or another (Department of Geological Sciences, California State University).

A simple classification of the different types of mass wasting can be:

  • Falls  (rock fall and rock avalanche)        
  • Slides  (rock slide, landslide and slump)      
  • Flows  (rock avalanche, debris flow, earth flow and creep).

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