Warm-up

Soil and Weathering Test Review

Weathering and Erosion

Weathering breaks down the rocks, erosion moves the particles, and deposition drops the sediments in another location.

Badlands National Park, South Dakota

Order1.Weathering2.Erosion3.Deposition

WeatheringThe process in which water, ice, and heat break down rock into smaller pieces, called sediments.

Arches National Park, Utah

Mechanical (physical) Weathering

1. Frost Wedging and Root/Plant Wedging

2. Exfoliation3. Abrasion

Physical Weathering – the breakdown of rocks and minerals into smaller pieces without a change in chemical composition.

Mechanical (physical) WeatheringFrost Wedging - alternate freezing & thawing of water

Root/plant wedging – plant roots growing into existing joints and fractures.

Exfoliation- outer layers of rock get stripped away over time

Abrasion- when rocks rub against each other

Chemical WeatheringThe breakdown of rocks and minerals into smaller pieces by chemical action.

7 Colors Hill, ArgentinaBadlands National Park, South Dakota

Chemical WeatheringOxidation- when oxygen unites chemically with a mineral. Ex. Rust (iron oxide)

Hydration- when water unites chemically with minerals.

Climate- the average weather of a location over time (precipitation and temperature)

Rates of Weathering

Surface area - If particle size goes down then weathering rate goes up

Rock type and composition

• Different minerals weather at different rates.

• Hard rocks weather slowly

• Soft rocks weather quickly

Rates of Weathering

Erosion and Deposition

Erosion – the removal and transport of weathered material by:

1. Wind 2. Gravity3. Glaciers4. Running water5. Living Things

Deposition –The process in which sediment is dropped and comes to rest

ErosionWind Erosion– hot and dry areas especially

Glacial Erosion– scrape and gouge, carry debris

ErosionRill erosion – caused when water runoff is heavy (after rainfall)

Gully Erosion – removal of large amounts of soil by heavy rainfall

Soil•Soil- made primarily of particles of rocks, minerals, and humus – decaying organic matter.

•Horizons- The layers of soil

Residual soil - Soil formed from the rock material beneath the soil.

Transported soil - Soil that has been moved from its place of origin.

•Topsoil- (A horizon) the top layer of mature soil containing organic matter and the most weathered rock.

•Subsoil - (B horizon) the layer below the topsoil made of partly weathered rock, clay sized particles, and very little organic matter.

•Bedrock- (C horizon) rock layer underneath useable soil

Soil Horizons

Parent Material

Humus- (O horizon) dead material on top of the soil column. Rich in

nutrients.

Not all horizons may be present!

Soil is the result of weathering and biological activities.

Humus “improves” the soil texture and helps it to hold water.

Can take 100 years for 1 cm of soil to form!

Soil Profile: The vertical

sequence of soil layers.

•Sand- any rock particle less than 2 mm but more than 0.05 mm

•Silt - any rock particle less than 0.05 mm but more than .002 mm

•Clay- any rock particle smaller than .002 mm

Soil Texture: classified according to % of the various sized grains: clay, silt, and sand.

30% Clay

50% Sand

20% Silt

Soil Type:Sandy clay loam

Soil Types• Often classified based on climate:

• polar• temperate• desert• tropical• other

• Climatic conditions are the main influence on soil development

Mass Movements1. Creep - Slow, steady, downhill flow of loose

materials – 3 cm/year2. Slides - Rapid, downslope movement of layer

of loose material 3. Mudflow - Swiftly moving mixtures of mud

and water4. Slump - Landslide along a curved surface5. Avalanche - Landslides of snow

All mass movements occur on a slope!

Glacial Erosion

• Glacier: large, moving mass of ice

• Weight of top layers exerts downward pressure forcing snow below to recrystallize into ice

If Formed in Valley:• Snow accumulation causes glacier to become

heavy and to flow downhill, due to gravity• Speed affected by slope, temperature, thickness

of ice and valley shape – 1mm/day

Valley Glaciers• Carve out U-

shaped valleys from bedrock

• The deep depressions where carved out from valley called a cirques

More rounded – U Shape