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Chapter 5 - Weathering and Soil
Midterm Number II
27
Geology
Undergraduate 1
10/18/2009

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Term
Weathering
Definition

the group of destructive processes that change the physical and chemical character of rock at or near the surface.

 

Term
Erosion
Definition

the picking up or physical removal of rock particles by an agent such as running water or glaciers.

weathering and erosion produce sediments that form sedimentary rocks.

Term
transportation
Definition
the movement of eroded particles by agents such as rivers, waves, glaciers or wind.
Term
mechanical weathering
Definition

the breaking up of rocks into smaller pieces

change in the rock is physical.

Term
chemical weathering
Definition

the decomposition or alteration of rock due to chemical weathering, acts fast on corners and edges.

decomposition of rock from exposure to water and atmospheric gases.

Term
spheroidal weathering
Definition
rounding of the rock due to chemical weathering acting more rapidly on corners and edges.
Term
differential weathering
Definition
different rock types weather at different rates, leads to landforms such as cliffs or slopes.
Term
talus
Definition
soft layers of rock weather to form shallow slopes of eroded rock debris.
Term
pressure release
Definition
reduction of pressure on a body of rock can cause it to crack as it expands.
Term
sheet joints
Definition
develop parallel to the outer surface of the rock as the outer part of the rock expands more than the inner part.
Term
exfoliation
Definition
process of spalling off of rock layers
Term
exfoliation domes
Definition
large rounded landforms developed in massive rock, such as granite, by exfoliation.
Term
frost action
Definition
the mechanical effect of freezing water on rocks, commonly occurs as frost wedging or frost heaving.
Term
frost wedging
Definition

results in expansion of cracks due to freeze/thaw cycles.

pries rock apart.

Term
frost heaving
Definition
lifts rock and soil vertically through freeze/thaw cycles.
Term
clay mineral
Definition
hydrous aluminum silicate with a sheet-silicate structure like that of mica.
Term
oxidation
Definition
oxygen from the atmosphere reacts with minerals, particularly iron bearing minerals like pyroxenes to produce iron oxides like hematite and limonite.
Term
dissolution by weak acids
Definition
some minerals such as calcite dissolve in weakly acidic ground water.
Term
feldspars are altered to form clays
Definition
acidic rain water and ground water react with feldspar minerals to produce clay minerals.
Term
temperature
Definition

higher temperatures generally lead to more rapid chemical weathering.

freeze/thaw cycles can lead to more rapid mechanical weathering through frost action.

Term
soil
Definition

a layer of weathered, unconsolidated material on top of bedrock.

contains organic material and can support plant growth.

Term
loam
Definition
a soil of approximately equal amounts of sand, silt, and clay.
Term
soil horizons
Definition

soil layers.

O - organic matter

A - organic matter mixed with minerals

E - leached zone

B - region of accumulation of clay and iron oxides

C - weathered fragments of bedrock

Term
residual soil
Definition
one that develops from weathering of the rock directly beneath it.
Term
transported soils
Definition
did not form from the local rock but from regolith brought in from some other region.
Term
laterites
Definition
highly leached soils that form in tropical regions where temps are high and rainfall is abundant.
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