Mass wasting

A mass movement, landslide or landslip is a geomorphological process, is continuously drawn in the soils, regolith and rocks under the influence of gravity down. Mass movements can occur in the form of creep, sliding, flowing, tipping or dropping - each with their own characteristics - and can take in their sequence between seconds and years. Mass movements take place both at the land surface as well as in submarine terrain and have also been observed on Mars and Venus except on Earth.

Overview

If the gravitational force acting on a slope and exceeds the frictional force, there is a mass movement. The strength and cohesion of the ground material, and the amount of internal friction help maintain the slope stability. One speaks in this context of the shear force. The steepest angle, the slope may have a cohesion -free, without loss of stability is known as the angle of friction. If a slope that angle, the shear keeps the gravitational force acting exactly in balance.

Mass movements can take place very slowly, especially in areas that are very dry or in which sufficient precipitation has fallen, so that a stabilizing vegetation cover could form. You can also carry a very high speed run, in the form of rock falls or landslides around, can have devastating consequences, which occur either immediate or delayed (in the form of a Abdämmungssees ).

Factors that can alter the potential of mass movements are: change of slope, weakening of the material due to weathering, increasing the water content, changes in vegetation cover.

Processes and forms of mass movements

Mass movement is one of the processes of areal erosion ( denudation ). In terms of their dynamics different types can be distinguished from mass movement:

  • Sturzdenudation and landslides have a high speed. The mass movements take place either by falling, sliding, flow or creep. Accordingly, various rapid mass movements can be distinguished: overthrow Rockfall, block fall
  • Rockslide
  • Landslide
  • Slump (rotational landslide block )
  • Landslide, landslide
  • Volcanic debris avalanche
  • Debris flow, mudflow, landslide
  • Lahar, mudflow in volcanic deposits
  • Solifluction ( floor tiles )
  • Soil creep, among other things, the formation of Plaiken
  • Talzuschub
  • Movement of debris and boulders
  • Rock glacier
  • Kriechdenudation is a very slow downslope movement of loose material. Creep can a continuous motion, induced Splash - creep caused by the continuous displacement of the material due to expansion and contraction processes of clay and water or in the rain.

The importance of water for mass movements

Water may increase or decrease depending on the amount of water present, the stability of a slope. Small amounts of water can strengthen soils because the soil as play an increased cohesion due to the surface tension of the water. This allows the soil to be more resistant to erosion than if it were dry.

However, if too much water is present, it acts as a lubricant, thereby accelerating erosion processes that result in different types of mass movement (eg landslides, mudslides, ...). Can well imagine you look at this, if you think of a sand castle. The sand must be mixed with water to keep its shape. If you add the sand too much water runs down the sand thereof; using too little water, the sand pile collapses because it can not be kept in shape.

Trigger for mass movements

Soils and regolith linger on a slope, as long as the gravitational force does not exceed the frictional force that holds the material in place. Factors that reduce this friction can be:

  • Seismic activity
  • Congestion by building
  • Increased proportion of soil moisture
  • Reduction in root density, which holds the earth in the underground
  • Weathering by frost heave
  • Bioturbation
  • Submarine gas hydrates

Swell

  • Monroe, Wicander: The Changing Earth: Exploring Geology and Evolution. Thomson Brooks / Cole, 2005, ISBN 0-495-01020-0.
  • Selby, MJ: Hillslope Materials and Processes, 2e. Oxford University Press, 1993, ISBN 0-19-874183-9.
  • AH and AN spotlight spotlight: Physical Geography, 3rd edition. UTB, Stuttgart, 2005, ISBN 3-8252-8159-0
  • Sebastian Krastel: Submarine landslides: a ( underestimated ) natural hazard, IFM -GEOMAR, Leibniz Institute of Marine Sciences at Kiel University, March 15, 2011, http://www.ifm-geomar.de/index.php?id=6099?
  • Erosion
  • Geomorphology
Computersimulation San Mateo County, California Sturzstrom Downhill creep Stone run Isfjorden (Svalbard) Frost heaving
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