A2 GEOGRAPHY REVISIONHAZARDOUS ENVIRONMENTS

9.2 HAZARDOUS ENVIRONMENTSRESULTING FROM MASS MOVEMENT

KEYTERMSANDDEFINITIONSMass movement is any large-scale movement of the Earth’s surface that is not accompanied by a moving agent. Landslide is a movement of a mass of rock, earth or debris down a slope. Landslides are divided into the following types of movement: falls, slides and flows. Mudslide is a rapid (up to 80 km/h) and fluid movement of a large mass of mud formed from loose material and water. Denudation is the wearing away of the Earth’s surface. It includes erosion, weathering and mass movements. Shear stress refers to the forces trying to pull a mass downslope. Shear resistance is the internal resistance of a slope.

KEYTERMSANDDEFINITIONSRegrading is the levelling of steep slopes into gentler ones. Avalanche is a rapid mass movement consisting of snow, ice, rock and debris. Wet avalanche is an avalanche consisting of partially melted snow. Dry avalanche is an avalanche consisting of fresh snow that has fallen off older snow. Pleistocene is the first epoch of the quaternary, preceded by the Pliocene and followed by the Holocene. It was a period of glacials and interglacials. The boundary between the Pliocene and Pleistocene is put at somewhere between 3 million years and 600 000 yrs ago (1.6 million yrs is sometimes taken as a middle ground boundary), whereas the boundary of the Pleistocene and the Holocene is generally regarded as being 10 000 yrs ago.

TOPICSUMMARYThe most important factors that cause mass movement are gravity, slope angle and water. ● Landslides are a common natural event in unstable, steep areas. ● Human activities can increase the risk of landslides. ● Methods to combat the landslide hazard are largely labour intensive and include building restraining structures such as walls, piles, buttresses and gabions; excavating and filling steep slopes to produce gentler slopes; and draining slopes to reduce the build-up of water and watershed.

TOPICSUMMARYAvalanches are mass movements of snow and ice. ● Avalanches are classified in a number of ways, such as by water content; e.g. dry or wet avalanches. ● Loose avalanches, comprising fresh snow, usually occur soon after a snowfall. ● Slab avalanches occur at a later date, when the snow has developed some cohesion. ● Meteorologists have warned that changes to weather patterns resulting from global warming will lead to increased snow falls in the Alps that are heavier and later in the season.

ADDITIONALWORK1. Outline the factors that contribute to increased shear stress and to

reduced shear strength. 2. Explain how human activity can increase the risk of landslides. Use

examples to support your answer.3. Explain how physical and human factors interacted to produce the

mudslides of Italy and Venezuela.4. Under what conditions are avalanches likely to occur? To what extent is

it possible to manage avalanches?5. Outline the natural and human reasons why landslides occur.6. To what extent can the risk of landslides be reduced?

SUGGESTEDWEBSITESwww.halcrow.com/Documents/geotechnics/Slopes_ Landslides_%20May10.pdf for examples of slope stabilisation and landslide management. http://iaeg2006.geolsoc.org.uk/cd/PAPERS/IAEG_522.PDF for a very detailed case study of landslide risk in an urban area.www.virtualmountains.ca for the Avalanche Education Project.www.chamonix.eu.com/some-things-you-probably-dontknow-about-avalanches for avalanche facts.