Download 5.1 Weathering

5.1 Weathering
*Weathering- key part of rock cycle
2 types
1. Mechanical
2. Chemical
*Mechanical Weathering- physical
forces break rock into smaller and
smaller pieces w/o changing its
composition.
3 processes
1. frost wedging
2. unloading
3. biological activity
weathering and erosion
*Frost wedging- mechanical breakup of
rock caused by the expansion of freezing
water in cracks & crevices.
-common in mountains
*talus-accumulation of rock debris at
base of a cliff
*Unloading- large masses of igneous rocks
may be exposed through uplift & erosion of
overlying rocks.
-outer rocks expand more than the rock
below.
*Exfoliation- slabs of outer rock break off in
layers (like onion peels)
-Ex. Stone Mountain, GA and Liberty Cap in
Yosemite
*Biological Activity- activities or
organisms
-tree roots breaking rock apart
-animals burrowing
*Chemical Weathering- transforms rock
into one or more new compounds
Ex. Rust, acid rain
http://www.youtube.com/watch?v=RUrk
bQXXRp8
Granite-chemicals dissolve and wash
away. Due to runoff, some of the quartz
debris ends up in rivers and oceans
contributing to beaches & sand dunes.
Spheroidal weathering- chemical
weathering can change the shape of
rocks. It wears away corners and edges
resulting in a rounded “Spherical” shape.
Spheroidal Weathering
Rates of Weathering
1. Rock characteristics- physical
characteristics such as cracks and
mineral composition
2. Climate- temp, moisture, & type of
vegetation
3. Differential weathering- different
parts of the rock weather at
different rates
Differential Weathering
-caused by different mineral composition
throughout rock
-caused by cracks and spaces
-results in Pinnacles