Soil Formation and Mass Movements

How does water cause mass movements? Bellwork: Pg. 143-145 How does water cause mass movements? How do earthquakes cause mass movements?

Climate determines soil formation

Soil Formations Tropical Climate Dry Climate Temperate Climate

Tropical Tropical (wet and warm) Climates make Laterite soils that are thick and infertile

1. Tropical Rain 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

3. Temperate 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

Pedalfer

Pedocal

Mass Movements

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

Triggers of Mass Movements Water – heavy rain and snow saturate the ground

Triggers of Mass Movements 2. Oversteepened Slopes – angles 25 to 40 degrees will hold loose particles. If a slope is steeper than 40 degrees, slips become more likely.

Triggers of Mass Movements 3. Removal of Vegetation – plant roots attempt to stabilize 4. Earthquakes

Classification of Mass Movements Mass movements are based on 3 things: Type of material that moves How it moves Speed of movement

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

Hinsdale County, Colorado 700 years old and still moving Slumgullion landslide Hinsdale County, Colorado 700 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)