Weathering, Soil, and Wasting
Unit 7 notes
Weathering

What is it?
◦ Disintegration and Decomposition of rocks

Where does it happen?
◦ At or near the surface of the Earth
Weathering

What does this process look like?
Weathering

Why does it happen?
◦ It is the response of Earth’s materials to the
changing environment.
Weathering

How many types are there?
◦ Mechanical
◦ Chemical
Weathering- Mechanical
A physical process
 Rocks are broken into smaller and
smaller pieces, each retaining the
characteristics of the original (parent)
material

Weathering- Mechanical

Frost Wedging
◦ Water enters and fills cracks in the rock. It
will expand when the water freezes and push
the rock apart more.
Weathering- Mechanical

Talus Slopes
◦ The pile of rocks that forms at the base of a
vertical rock formation. Most often the result
of frost wedging.
Weathering- Mechanical

Unloading
◦ Large scale loss of rocks off of the original
parent material
Weathering- Mechanical

Sheeting is also known as exfoliation.
◦ What is exfoliation on people?
Weathering- Mechanical

Sheeting◦ When large masses of rock (particularly
igneous) are exposed and large flat pieces are
broken off due to a reduction in pressure
Weathering- Mechanical

Thermal Expansion
◦ What happens when you heat something up?
◦ Cool something down?
Weathering- Mechanical

Biological activity
◦ Plants, animals (including humans), lichens,
mosses
◦ Plant roots will wedge in between rocks to
seek water. Lichens will actually digest the
surface of rocks for nutrients. And humans
will do what we do…
Weathering- Chemical

Carbonic Acid◦ H2CO3 is produced when CO2 dissolves in
H2O.
◦ Water vapor in the air undergoes this
reaction.
Weathering- Chemical

How carbonic acid works on Feldspar…
◦ 2 KAlSi3O8 + 2 H2CO3 + H20 
Al2Si2O5(OH)4 + 2KHCO3 + 4SiO2
◦ What it looks like…
Weathering- Chemical

Rocks that undergo this process tend to
take on a spherical shape.
Soil

“Science, in recent years , has focused
more and more on the Earth as a planet,
one that for all we know is unique-where
a thin blanket of air, a thinner film of
water and the thinnest veneer of soil
combine to support a web of life of
wondrous diversity in continuous change.”
◦ Jack Eddy 1993
Soil

Regolith
◦ The surface layer of the Earth that is
composed only of weathered rock and
mineral fragments
Soil

What is it?
◦ A combination of weathered mineral particles,
organic matter, water, and air

What makes for good soil?
◦ A mixture of approximately 50% regolith and
50% humus (decayed organic material)
Soil

This is where erosion fits into the mix.
Soil

As materials are eroded, certain minerals
and elements can be left behind or
concentrated to form ore and mineral
deposits.
Mass Wasting

Large movements of rock and/or soil in a
downhill direction
Mass Wasting

Triggers of mass wasting
◦ Water saturation
Mass Wasting

Triggers of mass wasting
◦ Oversteepened slopes
Mass Wasting

Triggers of mass wasting
◦ Vegetation- or rather removal of vegetation
Mass Wasting

Triggers of mass wasting
◦ Earthquakes