Download Weathering and Erosion

Erosion and Weathering
Erosion - the removal and transport of
earth materials by natural agents.
Some of these agents include glaciers,
wind, water, earthquakes, volcanoes,
tornadoes, hurricanes, mud flows, and
avalanches.
Glaciers
• Glaciers have caused extensive erosion in the
northern United States and around the Rocky and
Cascade Mountains.
• There are two different ways in which glaciers cause
erosion, by removing material and by depositing
materials.
• Some features caused by glaciers are:
• horns (pyramid shaped peaks)
• arêtes (knife shaped ridges)
• cirques (a bowl shaped depression found in
mountains)
• erratics (boulders )
• valleys
• tunnels
• lakes.
Volcanoes
• Volcanoes are the primary natural disasters
noted for erosion. They take materials from
inside the earth and spread them on the surface.
The volcano can eject these materials in several
different forms:
• Lava
• Pillow lava
• Tephra which includes all sizes of solid
fragments of lava from ash to blocks.
• Pyroclastics
Earthquakes
• Earthquakes may not seem like an
example of erosion, but they can be
considered as one. Earthquakes include
• the mass movement of rock
• friction between plates can wear away and
transport materials to a new location
• the shaking may initiate mud flows or
avalanches that can be very hazardous to
animals and plants alike.
Tornadoes and Hurricanes
• Tornadoes and Hurricanes could be
included with wind and water erosion.
• They accelerate the effects that wind and
water have on land forms.
• The wind speed in tornadoes can reach
500 km an hour and hurricanes have wind
speeds over 140 km per hour.
• These terrifying winds can move materials,
such as boulders, rocks, sands, and soils.
Wind
• Wind is one of the primary eroders, next to
water. Wind can erode by:
• Abrasion - Sand grains are the best tool in
abrasion, because it is made up of hard
minerals, like quartz. Desert sand blasts can
grind down boulders, usually into a smooth face
or facet
• Deflation - the process in which winds remove
loose rock particles from the surrounding area
• Deposition - depositing of sediments as well as
removing them.
Water
• The two main types of water erosion are that by streams
and that by waves.
• Stream erosion - can carry and deposit material, running
water in a stream can carry materials that attack the
bedrock of the river and create deeper valleys, materials
are then deposited at the mouth, or end of the river,
usually to form a delta.
• Waves erosion - storm waves can strike rock cliffs with a
force of thousands of kilograms per square meter,
bedrock can be split by water forced into cracks and
fissures, or scoured away by the grinding of sands and
pebbles, when waves break they cut away rock up to
their highest level and create an overhang, which
eventually creates a sea cliff.
Weathering is similar to erosion in that
it includes the breakup of rocks, just not
the transportation of the materials. The
specific definition of weathering is: the
breakup of rock due to exposure to the
atmosphere.
Chemical Weathering, also known
as decomposition, is when a rock's
minerals are changed into different
substances.
Chemical processes include acid
rain, acid etching by plants,
oxidation, and demineralization by
water
More than one of the processes
can occur simultaneously.
Elements Required for
Chemical Weathering:
-oxygen, carbon dioxide and other gases
from the atmosphere
-water from rain and snow
-minerals.
Solution
• Carbon dioxide is
dissolved in water and
forms carbonic acid
• When Calcite is exposed
to this acid it turns into
calcium bicarbonate
• Calcium bicarbonate is
soluble and is carried
away by water
• Broken up pieces of rock
are left behind
Sink hole near Stephenville,
Western Newfoundland
Hydrolysis
• Ions of water replace
ions of silicate
• The rocks fall apart and
the small ones are carried
away
• Clay is left behind – Bay
of Fundy
Oxidation
• Occurs mostly in igneous
and metamorphic rocks
• Oxygen is dissolved in
water and turns iron into iron
oxide
• The iron oxide is washed
away
• What remains is reddish
brown stained rock – can be
seen all around Clayton Park
Valley of Fire, Nevada
Mechanical Weathering
Mechanical weathering takes place when rock is
split or broken into smaller pieces of the same
material without changing its composition.
Mechanical processes include flash floods,
landslides, creep, exfoliation, root pry, frost action,
mud slides, abrasion, mass wasting, undercutting,
avalanches, and glaciers
Frost Wedging
• Frost wedging is caused by the repeated
freeze-thaw cycle of water in extreme climates
• Most rocks have small cracks in them, called
joints (or, tectonic joints). When it rains, rainwater
seeps into these joints. As the day cools and
temperatures at night drop below freezing, the
water inside the joints freezes.
• As water freezes into ice, it expands.
• The expanding ice places pressure on the
joints in the rock. Finally, when the pressure is
too much, the joint expands.
Root Prying
Roots force their way soil and rocks
causing rocks to split apart
Roots force their way under rocks pushing
them to the surface and apart from one
another
Thermal Expansion
• Exists in climates where there is
extreme hot and cold temperatures
• Rocks become very cold at night
(desert) and then are heated in the
daytime by the sun
• The rocks expand when they are
heated and shatter
Exfoliation or Sheeting
• Rocks that are formed under
great pressure within the
earth (Metamorphic) come to
the surface of the earth
• The pressure is no longer
present, so the rocks fall apart
• Usually in sheets, or layers
• This process is very
common in Canada especially
in the Canadian Shield