Release of PressureAs
removes material from the surface
of a mass of rock, pressure on the rock is
. This release of pressure causes the
outside of the rock to crack and
off like the layer of an onion.
Freezing and ThawingWhen
freezes in a crack in a rock, it
expands and makes the crack
.
The process of
also widens cracks in sidewalks and causes
in streets.
Animal ActionAnimals that
in the groundincluding moles, gophers, prairie dogs, and
some insects- loosen and
rocks in the soil.
Plant GrowthRoots of trees and other
enter the cracks in rocks. As roots grow, they
the cracks farther apart. Over
time, the roots of even small plants can pry
cracked rocks.
AbrasionSand and other
that are carried by wind, water, or
can
wear away exposed rock surfaces like sandpaper
on wood.