EARTHSC 1G03 Lecture Notes - Frost Heaving, Spheroidal Weathering, Crystallization

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CHAPTER 8: WEATHERING AND SOIL
Processes that alter rocks: weathering, erosion and transportation
Weathering: destructive processes that change the physical and chemical character of the rock
at or near the surface
Erosion: physical removal of rock particles by an agent such as running water or glaciers
Transportation: movement of eroded particles by agents such as rivers, waves, glaciers, or wind
WEATHERING
Alteration of Rocks:
Mechanical weathering: physical disintegration; break rock into smaller pieces
o Increases surface area
o Increases chemical weathering rate
Chemical weathering: decomposition of rock from exposure to atmospheric agents
o Proportional to the surface area
Effects:
Spheroidal weathering: rock has been rounded from initial blocky shape b/c weathering acts
quicker and more intense on corners than surface; example of “small scale exfoliation”
Differential weathering: varying rates of weathering in an area b/c differential resistance among
rocks to weathering
o Ex. Of resistant type: sandstone
o Ex. Of less resistant: shale
When weathered, shale forms gentle slopes of eroded rock debris called talus
MECHANICAL WEATHERING
Pressure release: reduction of pressure on top of a body of rock; causes rocks at depth to crack as they
expand upwards
Sheet joints: fracturing parallel to rock surface or in concentric layers develop parallel as outer
part of rock expands more
o Exfoliation: Process of spalling off of rock layers from the top
o Exfoliation domes: large, rounded landforms developed in massive rock by exfoliation
Frost Action:
Mechanical effect of freezing water on rocks
o Frost Wedging: water expands as it freezes in joints; this wedges the rock apart
Northern climates or mountainous regions
o Frost heaving: lifts rock and soil vertically
Evident in winter with bulging ground surface
Salt Crystallization:
Occurs when saline solutions enter cracks/joints and evaporate, leaving salt crystals; when
heated, salt crystals exert pressure on rock and decompose it
o Arid climates
B/c stronger heating results in stronger evaporation and more salt
crystallization
o Coasts
Other processes:
Plant growth roots growing in cracks thereby breaking up rock
o Break up of rock increases passageways for water and air to enter
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Document Summary

Processes that alter rocks: weathering, erosion and transportation. Weathering: destructive processes that change the physical and chemical character of the rock at or near the surface. Erosion: physical removal of rock particles by an agent such as running water or glaciers. Transportation: movement of eroded particles by agents such as rivers, waves, glaciers, or wind. Mechanical weathering: physical disintegration; break rock into smaller pieces. Chemical weathering: decomposition of rock from exposure to atmospheric agents: proportional to the surface area. Spheroidal weathering: rock has been rounded from initial blocky shape b/c weathering acts quicker and more intense on corners than surface; example of small scale exfoliation . Differential weathering: varying rates of weathering in an area b/c differential resistance among rocks to weathering: ex. When weathered, shale forms gentle slopes of eroded rock debris called talus. Pressure release: reduction of pressure on top of a body of rock; causes rocks at depth to crack as they expand upwards.

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