Weathering and Erosion
Processes That
Shape The Earth’s
Surface
Weathering and Erosion
Weathering - Weathering takes place
as rocks are broken down into
progressively smaller pieces by the
effects of weather. These pieces do
not move to a new location, they
simply break down, but remain next
to one another.
Erosion - process of removing Earth
materials from their original sites
through weathering and transport.
Causes of Weathered Rock
A large chunk of bedrock many hundreds of
feet long is broken down into smaller and
smaller pieces, until finally there are many
tens of thousands of small rocks. Often
rocks are broken down so much that they
become dirt.
Weathering is caused by water, as it freezes
and thaws, as well as by chemical
reactions that loosen the bonds holding
rocks together.
Weathering is most common at the surface
where exposed bedrock meets the
atmosphere. However, weathering can
extend many thousands of feet downward
into the Earth’s crust, following cracks,
fissures, and microscopic holes that allow
water to penetrate.
Mechanical Weathering
Mechanical weathering takes place when
rocks are broken down without any change
in the chemical nature of the rocks. The
rocks are essentially torn apart by physical
force, rather than by chemical breakdown.
The most common type of mechanical
weathering is the constant freezing, and
thawing of water. This is called Frost
Wedging.
Frost Wedging
Dome Exfoliation
Rocks break off into leaves or sheets along
joints which parallel the ground surface.
This is usually caused by the expansion of
rock due to uplift and erosion.
Dome Exfoliation
Biotic Weathering
The word ‘bio’ means life. Thus biotic
weathering is any type of weathering that is
caused by living organisms. Most often the
culprit of biotic weathering are plant roots.
These roots can extend downward, deep
into rock cracks in search of water, and
nutrients. In the process they act as a
wedge, widening and extending the cracks.
Plant Wedging
Chemical Weathering
Chemical reactions break down the
bonds holding the rocks together,
causing them to fall apart, forming
smaller and smaller pieces.
Chemical
Weathering
can form
some of the
Earth’s most
glorious
features
caves.
Transport Agents That Cause
Erosion
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Rain
Streams and rivers
Ocean/Beach Erosion
Ice (glaciers)
Wind Transport of Dust
Rain Erosion
Surface runoff forms when the rainfall
intensity causes the soil to reach its
saturation point.
Stream Erosion
Water flowing through a stream performs
three kinds of geologic work. Moving
water erodes material from the bed and
sides of the channel, it transports the
eroded material to a new location, and
then deposits it.
Stream Erosion and Deposition
Ocean/Beach Erosion
Beach erosion is defined by the actual
removal of sand from a beach to deeper
water offshore or alongshore into inlets, tidal
shoals and bays.
Glacier Erosion
A glacier is a moving body of ice. The glacier forms
when more snow and ice falls than melts and evaporates
from previous years. The pressure of the increasing
burden upon the snow converts the snow into ice. The
glacier carries with it the dirt, gravels, rocks and boulders
that it finds in its path as well as that embedded in the ice.
Wind Transport of Dust
Wind velocity plays a very important role in the
displacement of surface soil. Wind erosion physically
removes from the field the most fertile portion of the
soil.
Wind Transport of Dust
A View From Space
Weathering and Erosion Creates
and Changes Landforms
Canyons are formed with wind and water
erosion processes. The formation of a slot
canyon occurs when a channel begins
to erode a joint until it is carved,
cut, and forms a canyon.
Arches
A natural arch is basically a hole eroded
completely through solid rock.
Sand Dunes and Beaches
Beaches are deposition landforms, and are the
result of waves or currents moving the sand or
other loose material. Beach materials come
from erosion of rocks offshore, as well as
from land erosion.
Sand dunes are sculpted by wind. As long as streams
flow and lakes stay wet, the sediment in them is
protected. When lakes or stream beds dry out the
sediment is exposed to the wind and the particles are
ready to move! All it takes is a bit of breeze to put
fine sand in motion.
River Deltas
River deltas form at the
point where rivers join another
body of water. A delta is
formed by deposits of soil or
silt wherever a swift stream or
river empties into a lake,
ocean, or slower river. This
sediment and mud spreads out
into a fan- like shape, or delta,
across the mouth of the river.
Caves
Nearly all caves are formed from a
sedimentary rock called
LIMESTONE. Limestone is an
easy rock to break into smaller
pieces. If enough water keeps
hitting
the limestone, pieces will begin to
break off. This takes a lot of time.
Underground rivers beat against the
rock to form hollows. These
hollows
become bigger over time until a
cavern or cave is formed.
Natures Masterpiece….