Geog 331 Exam 1

Weathering

the break down and transformation of rocks and minerals through interacting physical and chemical processes

chemical weathering

decomposition- a chemical change in the nature of the original material

physical weathering

disintegration- process by which rocks are broken into smaller and smaller fragments without changing composition

often, rock is fatigued by repetitive stress

Weathering Debris

both weathering types operate simultaneously and affect the characteristics and rates of the other

Oxidation

occurs when an element loses electrons to an oxygen ion

occurs spontaneously above the water table

Iron is easily oxidized to the ferric state

Characteristic rusty red is indicative of oxidation weathering

Solution

earth material passes into solution by removal of its atoms

many common minerals are soluble in normal ground water

free ions go into solution

Solubility of a mineral is affected by:

temperature

pH

movement of water - leaching

crystal structure

Hydrolysis

the reaction between minerals and hydrogen ions from water

free cations usually dissolve in water

closely linke to solution reactions

important in the decomposition of feldspars and clays

Ion exchange

substitution of ions in solution for those held by mineral grains

most effective in clay minerals

ions to be exchanged have charges

governed by the pH of water: acidic allow H+ to replace metal cation

at high pH mineral cations remain in solution

Mobility

the extent to which chemical weathering alters the parent mineralogy depends largely on the relative mobility of constituent ions

leaching

downward movement of free ions in solution

regolith

all of the unconsolidated, loose deposits covering solid rock

very heterogeneous

saprolite

soft, thoroughly decomposed and porous rock, often rich in clay, formed by the in-place chemical weathering of rock

Soil

a componenet of the regolith profile

supporting plant life and soil organisms

Unconsolidated mineral or organic matter on the surface of the Earth that has been subjected to and shows effects of the genentic and environmental factors of:

climate, temp

parent material

Soil Profile

The vertical arrangement of the layers is a diagnostic property of soils

Layering develops in the weathering mass during the transition from being simply decomposed rock to being a true soil

Main components of soils:

mineral matter

air water

organic matter

Soil Properties

color

texture

structure

organic content

moisture retention

Paleosols

soils that formed on a landscape of the past

Buried soils

developed on a former landscape and subsequently covered by younger alluviumr

relict soils

were not subsequently buried but still exist at the surface

exhumed soils

were at one time buried but were exposed by erosion

Fastest chemical weathering rates occur in:

the tropics

warm/moist conditions

biotic

more chemical weathering

warmer and wetter

more physical weathering

colder and wetter

What is the most important control on regional topography?

tectonics

What kind of margin is the greater part of the western US along?

active margin

the east coast of the US is a:

passive margin

What tectonic movement regionally thickens the crust and builds mountains?

convergence

What is isostasy

an explanation for variations in crustal height over the earth.

What is airy isostasy

thickness of the crust controls topographic height

What is flexural isostasy

lithosphere is elastic and distributes loads over a broad region by bending

What processes remove and redistribute rocks and soil, and tend to control the fine-scale features of the Earth’s surface?

erosional processes