Soil Formation and
Mass Movements
Bellwork:Pg. 143-145
How does water cause mass movements?
How do earthquakes cause mass movements?
Soil Formation:
Climate determines
soil formation
Soil Formations1.Tropical Climate2.Dry Climate3.Temperate Climate
Tropical• Tropical (wet and
warm) Climates make Laterite soils that are thick and infertile
1. TropicalRain washes away the A Horizon, but rotting vegetation covers the B Horizon
Laterite
2. Desert•Desert (Dry) climates make soils from mechanical weathering•Soil is thin and mostly of parent rock (regolith)
3. Temperate• Temperate (cool to warm) climates make 2 soils that depend on rainfall.• Rain fall is not excessive
a. Pedalfer Soils – more than 65 cm of rain per year ex: clay, quartz, iron
b. Pedocal Soils –less than 65 cm of rain per year
ex: calcium carbonate
3. Temperate
Pedalfer
Pedocal
Mass Movements Definition• The transportation of
rock and soil down slope due to gravity
•Talus: a pile of rock fragments that accumulates at the base of the slope
•Together, weathering and mass movements
produce most landforms
•Streams and valleys are the most
common landforms on earth
• Why?
• Most mass movements end up in a stream or valley
1.Water – heavy rain and snow saturate the ground
2. Oversteepened Slopes – angles 25 to 40 degrees will hold loose particles. If a slope is steeper than 40 degrees, slips become more likely.
3. Removal of Vegetation – plant roots attempt to stabilize
4. Earthquakes
Mass movements are based on 3 things:
1.Type of material that moves
2.How it moves3.Speed of movement
Classification of Mass Movements
Types of Mass Movements…
1. Rockfall: rocks or fragments fall freely through the air =fast movement•Common on steep slopes & can trigger other mass movements
2. Slide: material moves suddenly along flat, inclined surface
Rockslide: slides including segments of bedrock
Slumgullion landslide
Hinsdale County, Colorado700 years old and still moving
3. Slump: downward movement of material along a curved surface•Leaves a crescent-shaped cliff
A slump is a type of slope failure which involves the rotational movement of soil or rock
4. Flows: materials containing large amounts of water
Earthflow – moves slowly
Mudflow – moves quickly
5. Creep: slowest type of mass movement. (freezing & thawing)