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Mass Movement Definition: Is the process by which material moves down a slope under the influence of gravity Type of material includes: Rocks, soil, stones, mud, and snow Causes = Natural processes ( weathering and erosion), Natural disturbances ( Earthquakes) or Human Activity ( dam collapse, forest clearance, road building) What factors influence mass movement??? 1. Gradient of slope, the steeper the slope the more likely that mass movement 2. Slope Material, if solid (compacted or cemented) less likely to move. 3. Water content: if large amount of water, it acts as a lubricant 4. Vegetation: roots help to bind soil and absorbs much of the rainfall 5. Tectonic Activity: triggered by volcanoes and earthquakes Classifying Mass Movement Type of mass movement Speed of mass movement Type of material Processes of Mass Movement Soil Creep Slowest type Occurs on slopes of less then 5 degrees Less then 0.5cm per year Terracettes Poles tilted Base of tree turned down slope Walls broken Slides Are sudden and rapid downward movements of masses of rock and soil under the influence of gravity. Rock Slides Occur along bedding planes, rocks slide along bedding planes down the slope at high speed (assuming slope is steep) Slumps Occur when the base of the slope is removed either by man or natural processes (undercutting). Spoon shaped sliding Flows Is a downhill movement of soft wet material (soil, clay, silt and peat) That has been made fluid by rain or melted snow Earth flows Local features, common on hill sides or valley sides especially after heavy rainfall Slow movement, produce bulges or lobes in the landscape, and leave scars on the landscape (no vegetation) Bog flow / Bog bursts Affects blanket bogs in upland areas. Peat soil Lots of rainfall Slieve Aughty Mountains in 2003 Mudflow Consists of 30% water Can occur after heavy rainfall, snow melt or volcanic eruptions in upland areas Water increases volume and acts as a lubricant Streams of mud like slurry pour down valleys 80 km per hour, very powerful LAHAR Associated with volcanic eruptions Nevado del Ruiz (Columbia, 1995) Hot magma and pyroclastic material melted snow and ice, water picked up volcanic ash and other material, moved down slope and killed over 21000 people in village of Armero. Fall Movement of a single rock or thousands of rocks, normally no soil cover High speed Very steep slope Speeds up to 300 km per hour Rock fall Can be triggered by freeze thaw, build up to form scree or talus slopes Rock Avalanche Rock fall dislodging other rocks and causing them to move down slope too. Human Influences on mass movement Over grazing…..sheep….Galway and Mayo… 2 million Soil erosion is common in upland areas Nephin area in County Mayo Connemara uplands in Co, Galway 30% has been seriously eroded Cause : high stock rates ( 5 times higher then UK) Rivers and lakes have been affected by silt loading Solution???? Sahel Region Narrow, semi-arid region between Sahara Desert to the North and equatorial forests to the south Natural vegetation = Savannah ( grassland and open woodland) People: Nomadic, moving to follow rains Moving between 5km to 10km a year Desertification Why??? Climate change (drought) Human Interference Cattle = number of cattle = wealth, cultural Between 1950 and 1970 rainfall was much heavier, so there was more pasture land 50% increase in the number of cattle Then drought hit, below average rainfall since below 1968 Result = Overgrazing Land stripped of its protective cover, vegetation unable to regrow, soil exposed, nutrients blown away in the wind Overcropping Population growth, high birth rates and immigration due to wars and drought Farmers began to settle not move, used land more intensively Crops like rice, maize and cash crops like nuts and cotton were grown in marginal land NO FALLOW YEAR No chance for land to replenish nutrients and yield was decreased Deforestation Very important for maintaining soil fertility Leaves form humus Roots bind soil together Wood is major energy source, 90% of heating and cooking and construction Soil is exposed Impact Lack of vegetation leaves soil exposed, any heavy downpours, water acts as a lubricant, mudslides and landslides are common