Mass Movement • A down slope movement of loose sediment and weathered rocks resulting from the force of gravity. • Erosion following weathering climatic conditions determine which materials and how much • All mass movements occur on slopes • Several variables influence mass movement • 1) Material weight result from gravity • 2) Materials resistance to sliding or flowing • 3) Trigger ie. Earthquake • 4) Water • Movement occurs when a force works and pulls materials is the stronger than its resistance • Erosion and undermining soil increases the materials pull down of the slope
MaSSmOVEMENT • Too little H2O does not stop material’s potential mass movement. • Increase H2O, weight of material increases and acts like a lubricant. With the force of gravity , mudslides. • H2O moves with material. It is not a transport agent.
Types of Movements • 1. Creeps • 2. Flows • 3. Slides • 4. Slumps • 5. Avalanches • 6. Rockfalls
Creep • Creep - slow/steady flow of loose weathered material. • Noticed over a long period of time. Indication - tilt of structures. • The slow, downhill movement of loose, water-logged materials that occurs in regions of permafrost is called solifluction.
Flows • Flows - materials flow as thick liquids. Speed - few cm’s per year to 100’s km per hour. • Swift mixtures of mud and H2O. Trigger - earthquakes, volcanic eruptions heat the earth. • Common in sloped, semi arid regions - short rain storms - ex. LA Basin
Slides • Slides - Rapid downward movements of earth materials that • occur - landslides - speed 200 km per hour. Stop at the bottom of slope as debris piles. Common - steep slopes. • Rockslides - type that occur when a sheet of mud moves down hill on a sliding surface. Trigger - Earthquakes.
Slumps • A slump is a mass of material in a landslide that rotates along a curved surface. • Locations of slumps are in areas of thick soil on moderate to steep slopes and highways. • Common after rain, reduces friction, forces between the center of the soil. • Slumps leave crescent shaped scars on the slope.
Avalanches • Avalanches - Landslides that occur in mountainous areas with thick accumulation of snow. - slopes 35°. • 10,000 avalanches occur in U.S. Sun melts the snow. • It reflects/ more snow added weight causing breakoff.
Rock Falls • Rockfalls - Occur at high elevations in step road cuts and on rocky shores. • Physical weathering process - breakdown - rock - rock falls straight down. • Human Factor - affect mass movement construction - heavy building - roads- weight helps makes slopes unstable. Leakage/septic tank seaps around.
Catastrophic mass movement - most common on slopes greater than 25° with annual rainfall of over 90 cm. • Preventative action for land movement: trenches along roads to catch debris; protective fencing; steel netting along slopes; retaining walls.
Wind • Wind transports material up hill and down erosional agents that are modified, ie. wind changes the landscapes in arid and coastal regions. • Ability to move material as less than H2O and ice. • Wind transports materials causing them to move different ways.
Methods of Transportation Strong winds - carry long distance (suspension) Saltation - Bounding motion of particles, ie. sand wind transport occurs in areas with little vegetation, ie., desserts, some arid areas, seashores and lakeshores
Wind transports material up hill and down erosional agents that are modified, ie. wind changes the landscapes in arid and coastal • regions. • Ability to move material as less than H2O and ice. • Wind transports materials causing them to move different ways.
Deflation Deflation - lowering of the land’s as surface result of movement. Problem - agriculture regions: 1930’s Dust Bowl - Sever dust storms - clouds of dust blown by the wind create deflation blowouts - shallow depressions
Abrasions • Abrasions - when particles such as sand rub against the surface of rocks and other materials. Rocks shaped by wind blown sediments are called ventifacts.
Wind Deposition Occurs in arid regions of change in wind velocity. Particles drop out of the air to the ground
Dunes Formation of Dunes - sand accumulates from the dropping of wind. A dune is a pile of wind blown sand. Conditions necessary for formation of dunes: 1) Availability 2) Wind velocity 3) Wind direction 4) Amount of vegetation
Desert Pavement - when finer sediments are blown away by wind and the heavier larger particles and pebbles are left behind. • Tallest dunes - Sands in Arabia - more than 100m in height • QuartzsSand - most common • Gypsum Dune - white sand - National Monument in New Mexico • Calcite Dune - Bermuda and areas of the Caribbean Sea
Loess - wind carries fine, lightweight particles, ie. Clay and silt • Loess deposits - Illinois, Iowa, Missouri, South Dakota, Nebraska
GlaciersThey shape the landscape by: a) eroding b) transporting c) depositing huge volumes of rock and sedimentsToday, scientists measure movements and size changes of glaciers to track climate change.
MOVING Masses of Ice • Glacier – a large moving mass of ice. • Formed near the earth’s poles and at high elevations in the mountains. • They cover only 10% of the earth.
Glacier Classification • Classified in two ways: • 1) Valley Glaciers - form in valleys in high mountainous areas, occurs when growing ice mass becomes too heavy to maintain its rigid shape and begins to flow. • Flow begins when the accumulation of snow and ice exceeds 20 meters in thickness.
Continential Glaciers • 2) Continental Glaciers - cover broad, continent sized Areas. • They form under the same climatic conditions as valley glaciers, but move in a different way. • The weigh of this glacier forces it to flatten is all directions. • These glaciers are also called ice sheets.
Glacier Erosion • Of all erosional agents, glaciers are the most powerful because of their great size, weight, and density when a valley glacier moves, it breaks off pieces of rock through a process called plucking. • When glaciers with embedded rocks move over bedrock valley walls, they grind out parallel scratches into the bedrock. • Small Scratches are called striations, larger ones are called grooves.
Glacier History • Scratches and grooves provide evidence of a glacier’s history and establish its direction of movements. • Glacier features include: • 1) cirques - deep depressions • 2) arete - where two cirques on opposite sides of a valley forming a sharp, steep ridge. • 3) horn - glaciers on three or more sides of a mountain top, a steep, pyramid shaped peak forms. Ex. Switzerland’s Matterhorn • 4) hanging valley - tributary valley that enters a U-shaped valley from high up a mountain side • 5) waterfalls • 6) U-shaped valleys