Mudslide is one of the most widespread geological events. It can engulf an entire village in an instant and can kill thousands of people and paralyze economy.
What are mudslides?
Mudslides are the most rapid fluid types of downslope mass wasting. They are the rapid movements of a huge mass of mud as a result of the combination of loose earth and water. Mudslides are also known as mudflows (not very liquid), debris flows (in high mountains), and mud stream or lahars (from volcanoes).
Mudslides have broad variety in terms of water content (from loamy mud to almost liquid) and material (sandy sediments, silt, wet soil, dirt, volcanic ash, rock debris, small plants and even trees). They also vary in terms of length and total velocity and mass.
Causes
Mudslides usually occur on sharply inclined slopes where vegetation cannot prevent rapid erosion. They can also occur on gentler slopes if certain conditions are met. Large volume of precipitation in short period of time and source materials that are easily eroded are other factors that can trigger mudslides. They are often secondary effects of earthquakes, volcanic eruptions, and heavy storms. Mudslides can occur in any climatic area but they are most common in arid and semiarid regions.
Characteristics
Mudslide deposits are sorted mixtures of organic materials, boulders, silt, and other debris. They have well-defined and abrupt edges, lobate appearance, and irregular surfaces. The deposits are extensive around the bases and on alluvial fans of many volcanoes.
Compared to stream flows, mudslides have a higher viscosity and density. They only deposit the coarsest part of its load, causing irreversible sediment entrainment.
The downhill mass wasting can speed as fast as 80 km/h to 100 km/h ( 50 mph to 60 mph). It may be as high as 3 m to 6 m (10 to 20 feet), but the high viscosity does not allow mudslides to flow far compared to a water flow.
Direct and indirect impacts
Mudslides can cost lives. In Venezuela, for example, the 1999 mudslide killed around 30,000 and left 140,000 people homeless. Trauma is very common in such catastrophe, causing many people to have short term and long term mental problems.
They may also severely damage essential services such as water system, electric system, health centers, hospitals, and lines of communication. Effects can also include loss of property value, crops, and livestock. This further heightens the vulnerability of the population.
