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5 th year Geography.  Causes of Mass Movement  Different types of Mass Movement  Case Studies of Mass Movement  Impact of Human Activities on Mass.

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Presentation on theme: "5 th year Geography.  Causes of Mass Movement  Different types of Mass Movement  Case Studies of Mass Movement  Impact of Human Activities on Mass."— Presentation transcript:

1 5 th year Geography

2  Causes of Mass Movement  Different types of Mass Movement  Case Studies of Mass Movement  Impact of Human Activities on Mass Movement

3  The movement of material downhill under the influence of gravity.  The loose material is called regolith.

4  Natural  Torrential rain  Heavy snow  Earthquakes  Volcanoes  Human  Road building across hills and mountains  Waste being piled on unstable slopes  Quarry blasting  Deforestation  Skiing

5  Gravity  Slope  Water  Vegetation  Human Activities  Type of Material

6  Can be grouped according to;  Speed  Water Content

7  Very Slow  Soil Creep  Solifluction  Fast and Dry  Rock Falls  Avalanches  Fast and Wet  Mudflows  Bogbursts  Lahars  Landslides  Slumps

8 Soil creep  Very slow movement  Underlying rock becomes heavily saturated following periods of heavy rainfall  Water can no longer pass through the rock  Soil particles expand and later contract when they dry out  Causes soil particles to creep slowly downhill under the influence of gravity


10 2. Slump-rotational slide  Loosely consolidated rock layers moves down slope  Influence of gravity  Moderate speed  May be an isolated occurrence or they may occur in large areas  Often associated with areas which have been affected by human activities  E.g. during the construction of roads where the land has been too steepened and has been left unstable  Also linked to coasts and river banks where, due to erosion, slopes have been undercut  Also associated with landscapes following heavy rain

11 3. Earthflow  Water saturated material (fine sand, silt and clay) flows downslope  Influence of gravity  Moderate speed  Generally occur on hilly slopes  Associated with heavy rain  Speed at which they travel varies from several cm per year to hundreds of metres per day  More common in humid areas  Tend to have a lower water content than mudflows

12 4. Rockfall  Rocks fall downslope  Influence of gravity  Rapid speed  Occur following periods of heavy rain and frost weathering  Strong earthquakes may also cause rock falls to occur  Caused by either a biological or a climatic event changing rock stability


14 5. Debris avalanche  Movement of rocks, soil and debris mixed with ice or water or both  Rapid movement  Material transported liquefies  Rapid speed  Can move further than the foot of a slope due to their rapid speed

15 6. Mudflow  Saturated regolith flows rapidly downslope  Influence of gravity  Associated with steep slopes and deep soils  Fast speed  Soil becomes waterlogged and saturated if there is an impermeable rock layer beneath  Can be of speeds in excess of 100 km per hour  Can occur as a result of volcanic activity – known as lahars  Volcano with snow on its top erupts, the melting snow and ice cause a mudflow

16 Mudflow case study  15 June 1991, Mount Pinatubo, Philippines  Volcanic eruption deposited more than 5 cubic kilometers of volcanic ash and rock fragments on the volcano slopes  Heavy rains washed this material down into the surrounding lowlands in giant, fast-moving lahars  The next four rainy season’s lahars carried about half of the deposits off the volcano, causing even more destruction in the lowlands

17 7. Bogburst  An area of bog moves downslope  Influence of gravity  Slow to fast speed  Tend to occur mostly during autumn and winter due to high precipitation levels  Periods of very heavy rain after long periods of very dry weather seem to be associated with the occurrence of bog bursts  Human activity is also linked to the occurrence of bog bursts, e.g. peat cutting, draining of land for agriculture and the construction of wind farms

18 Bogburst case study  Derrybrien, Slieve Aughty Mountains, Co. Galway  16 October 2003: bog had been affected by a dry spell during the summer and when heavy rain fell, the peat became saturated  Resulted in local roads being closed  Lough Cutra river system was polluted  Thousands of fish killed when some 70 acres of bogland flowed down river  Triggers- Human Activity & Heavy Rain



21 Avalanche  Very rapid movement of snow downslope  May occur due to either natural events or human activity  Fast speed  Usually occur on mountain slopes  Occur when the weight of the snow is too much for the slope to hold


23 Major causes of avalanches may include the following: 1. Weather – they are most likely to occur after a heavy snowstorm 2. Snowfall – recent snowfall exerts increased pressure on existing snow deposits 3. Temperature – warmer temperatures experienced over several days may cause upper layers of snow to melt and weaken 4. Wind direction – snow may be packed unevenly on the leeward side of a mountain due to prevailing wind direction 5. Slope angle – most avalanches occur on slopes of between 30 and 45 degrees 6. Slope orientation – most avalanches occur on slopes facing north, north-east and east 7. Human activities – deforestation and tourist activity may lead to the occurrence of avalanches

24 9. Landslide  Slope stability changes from stable to unstable  Causes may be loss of vegetation, erosion of slope, weakening of slope, earthquake activity, volcanic eruptions and human activities  Fast speed




28 Human activities can impact on the operation of surface processes  Impact of overgrazing  Impact of overcropping  Impact of deforestation

29 Sahel case study  Areas that are most affected by desertification are regions/areas that are on the edges of deserts  Sahel Region lies to the Southern end of the Sahara Desert in Africa  Covers an area of approximately 1000 km in total  Stretches from the Atlantic Ocean coast to the Red Sea coast and is located at the southern end of the Sahara desert  Desert is growing at a rapid rate  Experienced an increase in population in recent years

30 Sahel case study (continued)  High birth rate and immigration rates are also high  High population growth increases the demand for food  Increased demand for food and for land to cultivate  Growth of farming and cultivation has led to soil becoming exhausted and exposed to erosion  Increase in the number of animals required for food has also resulted in overgrazing  Cattle are also seen as a sign of wealth in the region.  Energy needs are satisfied by cutting down trees

31 Sahel case study (continued)  Vegetation, along with the trees, bind the soil together  When removed, the soil becomes weak and dry  When extra land is needed, a practice of ‘slash and burn’ has been used and has increased the barrenness of the region  The Sahel Region has experienced long periods of drought  Also experiences spots of unpredictable heavy rainfall  This type of rain can damage crops  When land experiences desertification, fertility is reduced and this has a direct effect on food supply; it may lead to famines

32  Saharan Desertification  Millions of years ago the Sahara was a green and pleasant land, but over the centuries desertification changed its climate.

33  Examine how human processes can impact on the process of mass movement. (30m)  Describe and explain any one process of mass movement. (30m)

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