Soil

Regolith: Rock and mineral fragments that cover the Earth from weathering.

Soil: the part of the regolith that supports the growth of plants.

3 important characteristics of soil 1. Soil composition: Soil contains mineral matter (broken down rocks) 45%, organic or humus (plant and animal) 5%, water 25% and air 25%.

2. Soil texture: clay, silt, sand mixtures. (Loams best for growth)

3. Soil structure: When soil clumps, factors play into cultivation, erosion, water penetration susceptibility.

How does soil form? 1. Parent material: the source of the mineral in soil.

2. Time: the longer a soil has been forming, the thicker it becomes.

3.Climate: Greatest effect on soil formation. Temperature and precipitation influence the rate, depth and type of weathering.

4.Organisms: living organisms have a huge impact on soil’s physical and chemical properties due to vegetation.

5.Slope: Steep slopes have more erosion so their soil is thin or nonexistent. Flat areas have little erosion so soil is thick.

What is a soil profile? A soil profile looks at the soil on down. Soil varies in composition, texture, structure and color at different depths. They are divided into zones called SOIL HORIZONS. They give us a SOIL PROFILE!

Horizons A Horizon: top soil  loose and partly decayed organic material on top. Then mineral mixed with some organic material B Horizon: Clay transported from above C Horizon: Partially weathered parent material. On top of a bed of unweathered parent material.

3 Common Types of Soil: 1. Pedalfers – temperate areas/ <63 cm rain per year/E. US/forested/ B horizons contain lots of iron oxide and aluminum rich clay/brown to red/ brown. 2. Pedocals – dry/ W. US / grassy and brush vegetation/ contains less Clay than E. US/ contain Calcite, calcium carbonate/ light gray-brown.

3. Laterite- hot, west tropics/ iron oxide and aluminum oxide/ orange or red color/when dried it makes bricks EX- temples/ poor soil due to quick decomposition/ lots of rain.

What is soil erosion? Soil erosion- loss of topsoil. Most abused human resource.

How does water erode soil? Water strikes the Earth’s surface and carries away dislodged particles. Thin sheets of water are called sheet erosion. Streams form rills, keep eroding, make trenches known as gullies.

What are rates of erosion? Human activities that remove natural vegatation such as farming, logging and construction have greatly accelerated erosion. Without plants, soil is easily carried away by wind and water. EX – 30s Dust Bowl.

How does sediment deposition pose as a problem to the environment? 1.Clogs up rivers 2.Fills in reservoirs- storage, floods, electricity 3.Holds pesticides- leaches into waterways

How can we help in controlling erosion? Although it’s difficult to do, we can begin with soil conservation by planting tree windbreaks, hill terraces, plowing on contours of hills, rotating crops, etc.

What is mass movement? Mass movement or mass wasting is the transfer of rock and soil downslope due to gravity.

What triggers mass movement? 1.water- heavy rains and rapid melting snow. 2.Oversteepened slopes – slopes greater than25 to 40 degrees can cause movement. 3.Removal of vegetation 4.EQs- most dramatic

How geologists classify mass movements? Geologists classify mass movements based on the kind of material that moves and the speed of the movement.

5 basic types of mass movement? 1.Rockfalls – rock or rock fragments free falling due to steep slopes and weathering. 2.Slides- 1 block moves and Causes rockslides. Most in high Montain regions. Over 200 km/ Per/hour/ rain or melting snow usually the cause.

3. Slumps – downward movement of a block on a curved surface. Slow and leaves crescent shaped cliff above slump.

4. flows- movement with lots of water. EX Mud flows. Earthflows move slowly over time. 1mm to several meters per day. 5.creep- mm to cm’s per year. Alternate freezing and thawing – slight hill.