ES Ch 5 Weathering, Soil & Mass Movements

weathering

breaking down and changing of rocks at or near Earth's surface

mechanical

occurs when physical forces break rock into smaller and smaller pieces without changing the rock's mineral composition

Frost wedging, unloading (exfoliation), and biological activity

What are 3 types of mechanical weathering?

frost wedging

water finds its way into cracks in a rock & when the water freezes, it expands which enlarges the cracks in the rock & over time the rock breaks into pieces

talus

sections of rock that are wedged loose & tumble into large piles that commonly form at base of steep, rocky cliffs

unloading

reduced pressure on rock that occurs when large masses of rock are exposed through uplift & erosion

exfoliation

when pressure on rocks reduced, the outer layers of rock expand more than rock below & slabs of outer rock separate like layers of an onion & break loose

biological activity

activities of organisms (plants, burrowing animals & humans)

chemical weathering

transformation of rock into one or more new compounds

water

What is the most important chemical agent?

oxidation

oxygen dissolved in water reacts easily with certain minerals (iron will rust), forming oxides

carbonation

carbon dioxide dissolved in water forms carbonic acid which can dissolve limestone

acid precipitation

Water in the atmosphere also absorbs sulfur oxides and nitrogen oxides (oxides are produced by the burning of coal and petroleum) that produce acids

spheroidal weathering

the rounding of rock due to more rapid weathering of corners and edges

differential weathering

when different parts of rock mass often weather at different rates

regolith

layer of rock & mineral fragments produced by weathering that covers nearly all of Earth's land surface

humus, water, air, minerals

What are the 4 components of soil?

humus

organic, dark material remaining after decomposition by microorganisms

loam

soils are usually best for plant growth

parent material

source of mineral matter in soil

transported soil

parent material was moved from another location by gravity, water, wind, or ice

climate

has greatest effect on soil formation

plants

What is the main source of organic matter in soil?

hardpan

compact, impenetrable layer made of clay

topsoil

A soil horizon

subsoil

B horizon

C horizon

contains partially weathered parent material

pedalfer

usually forms in temperate areas that receive more than 63 cm of rain each year, found in eastern US

pedocal

found in drier western US in areas that have grasses & brush vegetation

laterite

form in hot wet tropical areas

sheet erosion

thin sheets of water move the soil particles across surface

rills

A tiny groove in soil made by flowing water

gullies

deep ditches formed after heavy rainfall

mass movement

the transfer of rock and soil downslope due to gravity

gravity

What is the primary force that causes mass movements?

rockfall

occurs when rocks or rock fragments fall freely through the air

slides

block of material moves suddenly along a flat, inclined surface

rockslides

slides that include segments of bedrock

slump

downward movement of a block of material along a curved surface

slump

leaves a crescent-shaped cliff

flows

mass movements of material containing a large amount of water, which move downslope as a thick fluid

mudflows

flows that move quickly & are common in semiarid mountainous regions

earthflows

flows that move relatively slowly—from about a millimeter per day to several meters per day

creep

slowest type of mass movement which usually travels only a few millimeters or centimeters per year