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 Formations

1. Tropical Climate

2.Dry Climate

3.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

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 moves

3.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, 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)