Weathering, soil, and mass movement

Question 1

What is mechanical weathering?

Answer 1

Physical forces break rock into smaller pieces w/o changing the rocks mineral composition.

Question 2

What are the 3 important physical causes of mechanical weathering?

Answer 2

• Frost wedging
  
  • Water freezing in cracks
  • Form “talus” piles
• Unloading
  
  • Igneous rock is uplifted and expands, breaking off in layers (exfoliation)
  • Example: yosemite
• Biological activity
  
  • Plants
  • Burrowing animals (worms)
  • Humans

Question 3

What is chemical weathering?

Answer 3

Transformation of rock into new compounds.

Question 4

What are the 2 factors that affect the rate of weathering?

Answer 4

• Rock characteristics
  
  • Mineral composition/solubility
  • Physical features (joints)
• Climate (temperature/moisture)
  
  • High temps leads chemical weathering.

Question 5

What is the Regolith?

Answer 5

The layer of rock and mineral fragments that covers most of the Earth’s land surface. Includes “soil” which supports the growth of plants.

Question 6

What are the 4 major components of soil?

Answer 6

• Mineral matter or broken-down rock.
• Humus (decayed remains of organisms)
• Water
• Air

Question 7

What is the composition of “good quality” soil?

Answer 7

• 25% air
• 25% water
• 45% mineral matter
• 5% humus (organic matter)

Question 8

What are the characteristics of soil?

Answer 8

• Texture (partical sizes)
  
  • sand->silt->clay
  • Loam (mix of all 3 sizes) is best.
• Structure

Question 9

What are the 5 most important factors in soil formation?

Answer 9

• Parent materials (resident bedrock or tranported materials)
• Time (soil layer becomes thicker over time)
• Climate (bigest factor)
• Organisms (bodies and mixing)
• Slope
  
  • Steep slopes have poor soil
  • Orientation N/S affects temp/moisture.

Question 10

What are the 3 soil horizons?

Answer 10

Soil composition/texture/structure/color varies with depth. The 3 horizons/zones/layers of soil are:

• A (topsoil)
• B (subsoil) - clay particals washed down from A
• C - soil between B and parent material

Question 11

What are the 3 common types of soil?

Answer 11

• Pedalfer
  
  • Dev under forest vegitation
  • Iron oxides / aluminum clays in B horizon.
• Pedocal
  
  • Dev under drier grasslands
  • Accumulates calcium carbonate
• Laterite
  
  • Dev in hot/wet tropical climates
  • Intense chemical weathering

Question 12

What is “Mass Movement”?

Answer 12

Transfer of rock/soil downslope due to gravity.

Question 13

What factors commonly trigger mass movement?

Answer 13

• Saturation of surface material with water.
• Oversteepening of slopes (erosion/roads)
• Removal of vegetation (man/fire)
• Earthquakes.

Question 14

What are some ways to control erosion?

Answer 14

• Planting trees in rows (windbreaks)
• Terracing hillsides
• Plowing along the contours of hills
• Rotating crops.

Question 15

What are the types of mass movements?

Answer 15

• Rockfall (fragments falling freely)
• Slides (block of loose material lets loose).
• Slump
• Flows (w/water, e.g. mud flows)
• Creep (slow downhill movement of soi)