Download Weathering and Erosion

Weathering & Erosion
Weathering
Weathering – the process
by which natural forces
break down rocks
Types of Weathering
•Mechanical Weathering
•Chemical Weathering
Rate of Weathering
•Surface Area – the more of a rock’s surface
that is exposed to air and water, the faster
the rock will break down because there are
more surfaces to be weathered
Rate of Weathering
•Rock Composition – different kinds of rocks
break down at different rates, because some
rocks contain softer minerals than others
Rate of Weathering
•Climate
•Chemical weathering
occurs faster in hot,
wet regions
•Mechanical
weathering caused by
freezing and thawing
occurs more in cold
regions
Weathering
•Mechanical
Weathering – the
breakdown of
rocks into smaller
pieces of the same
material without
any change in its
composition
Mechanical Weathering
•Ice Wedging – when water
freezes in the cracks and
pores of rocks, the force of
its expansion is strong
enough to split the rocks
apart
•Occurs where there are
frequent freezes and thaws
•Can cause potholes to form
in pavement
Mechanical Weathering
•Abrasion – the process of wearing down
by friction (wind and water)
Mechanical Weathering
•Pressure Release – Earth’s
forces can push rock that
formed underground up to
the surface, the release of
pressure causes the rock to
expand and crack
•Exfoliation – in geology,
the process in which layers
or sheets of rock gradually
break off
Mechanical Weathering
•Plant Roots –
when plants grow
in cracks in a
rock, their roots
can widen the
cracks and force
the rock apart
Weathering
•Chemical
Weathering – the
breakdown or
decomposition of
rock that takes place
when minerals are
changed into
different
substances
Chemical Weathering
•Dissolving – the
slightly acidic water
breaks down minerals
in rocks
•Acid rain can cause
holes to form in rocks
and/or smooth out
rough edges
•Carbonic acid in water
dissolves calcite, which
can hollow out
underground caverns
Chemical Weathering
•Rusting –
oxygen in the air
and water
combine with
iron to produce
iron oxides, or
rust
Soil Destruction
•Farming
•Farmers clear trees and
other plants and plow up the
soil to plant crops, but
without its natural plant
cover, the soil is more
exposed to rain and wind
and therefore more likely to
get washed or blown away
•Overgrazing by animals
destroys natural vegetation
and causes the soil to wash
or blow away more easily
Soil Destruction
•Construction
•Exposed soil at
construction
sites washes or
blows away and
ends up in
nearby water
sources
Soil Destruction
•Mining
•Exposing rocks
and minerals to
the air and
rainwater speed
up the rate of
chemical
weathering
Soil Destruction
•Desertification –
the expansion of
desert conditions
in areas where the
natural plant cover
has been
destroyed
Soil Conservation
•Crop Rotation –
the practice of
planting different
crops on the same
field in different
years or growing
seasons to
maintain soil
fertility
Soil Conservation
•Conservation
Tillage – a system
of cultivating the
land that reduces
soil and water loss
by leaving at least
30% of the crop
residue on the
surface at the time
of planting
Soil Conservation
•Terraces – flat,
step-like areas
built on a hillside
to hold rainwater
and prevent it
from running
downhill
Soil Conservation
•Contour Plowing
– the practice of
plowing along the
curves, or
contours, of a
slope helping
channel rainwater
so it doesn’t run
straight downhill
Soil Conservation
•Windbreaks –
rows of trees
planted
between fields
to reduce the
force of winds
that can carry
off soil
Erosion
•Erosion – the process in
which sediment is picked
up and moved from one
place to another
•Deposition – the process
in which transported
sediment is laid down
•Mass Wasting – the
downhill movement of
loose rock or soil
Erosion
•Rockslide – a
large mass of
rock slides as a
unit down a
slope
Erosion
•Mudflow – a
mixture of soil,
water, and
debris flowing
downward,
picking up
sediment as it
rushes down
Erosion
•Slump – a
slide of loose
debris that
moves as a
single unit
Erosion
•Creep – the soil closer to the surface
moves faster than the soil farther down
Glaciers
Glacier
•A mass of ice that exists
year-round and moves
over land
•Glaciers move lots of
sediment that can carve
striations (grooves) into
rocks
•The glacier deposits
debris as it melts
Glaciers
•Alpine Glacier –
form in
mountains and
flow down
through valleys
(also called valley
glaciers)
Glaciers
•Continental
Glacier – much
larger than alpine
glaciers, they can
cover entire
continents (also
called ice sheets)
Glaciers
•Till– sediment
of different
sizes left
directly on the
ground by a
melting, or
retreating,
glacier
Glaciers
•Erratic– large
boulders left
behind by
glaciers
Glaciers
•Kettle Lake – a
bowl-shaped
lake that was
formed as
sediment built up
around a block of
ice left behind by
a glacier
Running Water/Stream Erosion
Streams
•Flowing water will lift and carry small
sediments such as silt and sand
•Where water moves more swiftly there will
be more erosion
Running Water/Stream Erosion
•Where the water slows down, sediments
will be deposited
•The steeper the slope, the faster erosion
will occur
Stream Erosion
•Meander – curves
and bends that
form a twisting,
looping pattern in
a stream channel
Water Erosion
•Oxbow Lake – a
crescent-shaped lake
formed when a stream
cuts a new channel
that by-passes a
meander during a
flood
Stream Erosion
•Waterfall–
soft rock
erodes,
leaving a hard
ledge over
which the
stream falls
Stream Erosion
•Delta– an area of land formed by the
buildup of sediment at the end, or mouth,
of a river
Stream Erosion
•Floodplain– the area of land on either side of a
meandering stream that is underwater when
the stream floods
•Often have rich, fertile soils due to minerals
and fine sediments that have been deposited
by past floods
Stream Erosion
•Canyon– the result of a stream cutting its
way deeper and deeper through the
underlying rock layers
Stream Erosion
•Cave– forms as
acidic rainwater
chemically reacts
with limestone or
dolomite rock layers
underground, slowly
creating larger and
larger spaces as the
rock is worn down
and washed away
Stream Erosion
•Sinkhole – a basin that forms when the
roof of a cave becomes so thin that it
suddenly falls in
Wind Erosion
Wind Erosion
•Carries fine, dry sediments over long distances
•Can carve out landscapes as it carries sediment
•Loess: fine particles of silt and clay deposits
Wind Erosion
•Dune – a mound of sand built up by wind
Wind Erosion
•Desert Pavement –
the layer of stones
and gravel left
behind after wind
blows away all the
smallest particles of
sand and silt
Wave Erosion
Waves
•The crashing of
waves on a
shoreline combined
with storms
continually shape
the beach
•Tidal action and
waves carry away
weathered
materials
Wave Erosion
•Longshore
Drift – the
zigzag
movement of
sand along a
beach, caused
by the action
of waves
Wave Erosion
•Sandbar – a
ridge of sand
built up by the
action of
waves and
currents
(under water)
Wave Erosion
•Barrier Island – a
long, narrow island
that develops
parallel to a coast
as a sandbar builds
up above the
water’s surface
Wave Erosion
•Sea Arch– a
natural
opening
eroded out
of a cliff
face
Wave Erosion
•Sea Stack–
a steep,
vertical
column of
rock near a
coast
Wave Erosion
•Sea Stump–
the collapsed
remnants of
an eroded sea
stack