Lecture 7// Weathering

Question 1

Weathering (4)

Answer 1

The breakdown of menials and rocks by mechanical (physical), biological, or chemical processes.

Susceptibility to chemical and physical weathering differs amongst minerals and rocks; some being more stable than others:

• Olivine & Pyroxene is the least stable
• Quartz is the most stable

Question 2

Erosion (1)

Answer 2

-The transport of weathered material.

Question 3

Physical weathering (4)

Answer 3

-Mechanical breakdown of minerals and rocks without a change to its chemical composition. (abrasion, freeze-thaw, hydraulic action, pressure release)

Question 4

Abrasion (3)

Answer 4

Grain-to-grain contact:

• sand blasting by wind
• pebbles and in the bedload of a stream

Question 5

Freeze-thaw (1)

Answer 5

-Water fills cracks during the day and freezes overnight, expanding slightly in volume and thus widening the crack bit by bit with each freeze-thaw cycle.

Question 6

Talus (2)

Answer 6

• A cone of weathered debris at the base of a hill, formed by rock fall material from above.
• ex. Rockville, Utah, near Zion National Park.

Question 7

Hydraulic action (2)

Answer 7

from waves at high tide erodes the base of the cliffs, creating overhangs and sea cliff retreat.
-ex. coastal weathering and erosion in New Zealand.

Question 8

Pressure release (9)

Answer 8

Tectonic uplift over geologic time results in weathering and erosion.
-Expansion of once deeply buried rock results in joints (fractures).

Commonly results in vertical, parallel joints which weathering is greatest due to its larger exposed surface area.

• Over time produces parallel ridges, and differential ridges producing arches and rock pedestals.
• ex. sandstone ridges in Arches National Park, Utah
• ex. delicate arch in Arches National Park, Utah
• ex. balanced rock in Arches National Park, Utah

Pressure release also occurs in uplifted plutonic rocks. Forming sheet (curved) joints.
-ex. sheet joints and exfoliation (resulting in small rock slide) near Porteau Cove

Question 9

Biological weathering (3)

Answer 9

Disintegration of rock physically of chemically by living organisms:

• Tree roots: physically breaking rock apart.
• Lichen: chemical breakdown by symbiotic fungus and algae.

Question 10

Chemical weathering (6)

Answer 10

The chemical decomposition of minerals in rock:

Dissolution: Minerals dissolved fully and are washed away by rain water.
-ex. dissolution of calcite in limestone resulting in features of karst topography (dissolution of water sources in an environment (streams) causing sinkholes and karst caverns)

Hydrolysis, Oxidation: Minerals form as a weathering product, in addition to some compounds dissolving.

• ex. hydrolysis of feldspar (KAlSi3O8) resulting in kaolinite (Al2Si2O5(OH)4); in solution: K+ ions and silica (si & O)
• ex. oxidation of ferromagnesian silicates in granodiorite (fractured rock exposed)