Landforms and Weathering
Transcript Landforms and Weathering
Landforms and Weathering
Major Unit Goal/Learning Outcomes
• Students should be able to:
Describe how forces change landforms over time
Rate the effects of weathering forces
Understand how water movement shapes landforms
Describe the characteristics of landforms
Discuss how water flow effects erosion
Identify landforms using maps and aerial photographs
Understand the influence of humans on erosion and
• Identify and analyze forces that cause change
in landforms over time including:
– Water and Ice
• Investigate and discuss the role of the water
cycle and how movement of water over and
through the landscape helps shape land
• Discuss and consider the wearing away and
movement of rock and soil in erosion and its
importance in forming:
• Describe the deposition of eroded material
and its importance in establishing landforms
• Flood Plains
• Discuss how the flow of water and the slope
of the land affect erosion.
• Identify and use models, maps and aerial
photographs as ways of representing
• Discuss and analyze how humans influence
erosion and deposition in local communities,
including school grounds, as a result of:
– Clearing land
– Planting vegetation
– Building dams
What are Landforms?
• Landforms are the natural features of the
• Mountains, plateaus, plains and hills are all
examples of landforms.
Changes Over Time
• Landforms constantly develop and change as
the forces of weathering and erosion change
rocks and break them down. Weathering is
the force that causes rocks to fragment,
crumble, crack and break down either
chemically or physically.
Weathering of Rocks
• Rocks weather in different ways and at
different rates depending on the mineral
composition and location of the rock. The
rocks break down into small rock fragments as
they are weathered. These fragments are
broken down further into particles that
comprise soil along with organic material.
When water is frozen it expands, so when
water seeps into cracks in rocks then freezes,
the expanded ice can cause the rock to split
and crack. This process is known as ice
wedging and it can reduce a rock to rubble
• Soil can also collect inside of the cracks of
rocks. Plants can grow in this soil and
eventually the roots grow large enough to
cause pressure on the rocks, causing the crack
to expand. The rock can split apart from this
• Minerals found in the rocks can change to
other minerals due to the reaction with water
or air. Reactions such as rusting or acid
formation can also cause the rock to break
down into smaller fragments.
Changes Over Time
• Erosion carries away the rock debris caused by
weathering. The eroded rocks and sediments
are deposited by forces such as volcanoes,
wind, water, ice and waves to various
depositional environments on Earth’s surface.
• A variety of landforms are carved by water.
Moving water erodes rocks and transports the
small pieces of rock.
• Groundwater or underground water can
dissolve limestone causing caverns or
• Ocean waves shape our coastline. The waves
also transport sand and rocks causing
• Wind moving at high speeds can transport a
large amount of dust and sand.
• Erosion of this type shapes deserts by carrying
the sand and by sandblasting rock. If soil
doesn’t contain plants to hold its place, it can
be exposed to vast amounts of erosion.
• Loss of soil can cause loss of farmland.
1930 Dust Bowl
• During the Dust Bowl in the 1930’s, over
cultivation of the farmland removed the
native grasses that held the soil in place.
• Drought and wind stripped the land of its
• Glaciers also help to shape landforms. These
huge sheets of ice move slowly over the land
in the polar regions of the Earth and in high
mountains where vast amounts of snow build
up and turn to ice.
• The mass of ice moves slowly, only a few
inches per day. This movement is caused by
layers of ice moving each other or by the
layers of ice sliding on a thin layer of water
that begins to melt at the bottom of the
• As the glaciers moves, it pull out pieces of the
bedrock which become embedded into the
bottom of the glacier.
• As the glacier moves over the land, these
pieces of embedded rock grind down on and
under the glacier, shaping a variety of
• When glaciers retreat, possible landforms that
are created include: canyons, huge boulders,
rock piles, hills, valleys and lakes.
Forces that Build
• Plate tectonics is a major force that builds
large masses of land.
• Faults, volcanoes and mountains are formed
as rocks are moved across the surface of the
Earth and shape mountains.
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• There are smaller building forces that can
occur by transporting weathering agents such
as water, wind and ice.
• These are the same forces that erode the land.
• These weathering agents can carry sediment
and deposit it somewhere else through a
process called deposition.
• Deposition of sediment can form beaches,
deltas, sand dunes and change
• the shape of rivers and
People and the Land
• People have a direct affect on weathering, erosion
• People can speed up erosion by clearing the land for
farming, housing developments, building roads,
deforestation and strip mining.
• People change the course of rivers by channeling
them and building dams across them
• The shapes of mountains are changed by building
roads and highways.
• Coastlines are changing by building roads and houses
that may alter the natural changes of the coastline.
Examples of Landforms:
• Valleys are depressions on the surface of the
Earth that are borders by hills or mountains.
• The naturally formed troughs are made by
water and/or ice (glacier) erosion.
• As rivers and streams flow through valleys,
they carry sediments and other materials of
• Fertile soil is found at the bottom or floor of
the valley. The valley floor slopes
Valleys formed by rivers have more v-shape.
U-shaped valleys are formed by glaciers.
• Plateaus are formed in different ways:
– Some are formed as a result of lava flows covering
a large area and building up the surface.
– They can also formed by the forces of upward
folding, followed by the erosion of surrounding
land. These forces leave large areas of fairly level
highlands that are separated from land by steep
• Plateaus can be surrounded by mountains or
can be higher than the land around them.
• Mountains are created by huge forces in the
Earth over a long period of time.
• They are formed by the movements of the
Earth’s plates (plate tectonics).
• The forces of heat and pressure underneath
the Earth’s crust cause movements in the
• These movements are what most scientists
believe form most of the mountains.
• The lithosphere of the Earth is divided into
sections called plates.
• Through plate tectonics these plates move
and collide, separate, and slide past each
• When some plates collide, one moves under
the other and causes the eruption of
• Other plates compress causing folding and
wrinkling of the crust. (Appalachian Mts.)
• Plains are wide stretches of land that do not
have significant changes in elevation.
• Some plains (Great Plains) are found inland
while others found along the coast.
• Plains contain fertile soil so these areas are
often well populated.
• Roads, towns and cities are also easily built in
• Coastal Plains are stretches of lowland along
the seacoast that slope towards the ocean.
Along the NC coast, the coastal plain is
flooded by the ocean and the edge of the
North American continent is actually
submerged beneath the ocean. In some areas
the plains is part of an elevated ocean floor.
• Sediments and other solid materials are
carried by rivers and waves where they are
deposited along the coastline extending the
• The sharp upward slope of land along the
plain’s inward is called the fall line.
• Lakes are bodies of water that are different
from marine environments.
• They are small, fairly closed systems, and have
less pronounced tides.
• When sediment flows into lakes, the coarser
sand and gravel are deposited in the shallow
areas of the lakes, especially during the
• The finer silt and clay are deposited in the
deeper areas of the lakes, especially during
• Alternating thin layers of light-colored and
dark colored finer grained sediment are called
varves, this is one type of deposit and forms in
all types of lakes (glacier and nonglacial).
• While most sediment deposits in lakes come
from rivers, some deposits are from wind, icerafting and volcanic rock erosion.
• Volcanoes create different types of rocks
because of the various mineral compositions
that compose magma.
• Depending on the amount of gas found in the
magma and the thickness of magma, the
volatility of volcanic eruptions and the
landforms that are made differ.
• Lava in mountain building environments is the
most thickness and has higher gas content.
• The eruptions from these volcanoes are more
explosive and form an extrusive, solid volcanic
material called tephra.
• Rich fertile soil is formed from ash and is used
for growing crops.
• In the USA most volcanoes are found in
Hawaii, Washington and Oregon.
• As a results of volcanic activity, there are three
different types of landforms that are created.
1. Lava Plains and Lava Plateaus are volcanic
landforms that are created when a large volume
of fluid lava flows over a wide surface area.
The result is topography with extremely
flat surfaces that aggrades with each
successive lava flow.
Volcanic composite cones
• Composite cones are very distinctive in
• They have layers of interbedded, blocky
tephra that is composed mainly of ash and
• The peaks can rise several thousands of
meters with narrow circular bases.
• Mount Rainer in Washington is an example of
a composite volcano.
• These are created by volcanoes that have
erupted then have later collapsed inward.
• Composite cone volcanoes are much more
likely to form calderas due to the tephra
sheets that they contain.
• Crater Lake in Oregon and Yellowstone Plateau
in Wyoming are calderas.
• Not all landforms are created by deposition.
• The Grand Canyon is a landform that was
created by the erosive forces of water and
wind that cuts and etched the land over
millions of years.
• The Colorado River cut deep gorges into less
resistant rock and created the canyon while
the more resistant, less weathered rock
Other Types of Landforms:
• Alluvial deposits are rock debris and
sediments such as silt and clay that are carried
down by mountain streams or rivers to the
• Alluvium is soil or sediments deposited by a
river or other running water.
• Alluvium is typically made up of a variety of
materials: fine particles of silt or clay, larger
particles of sand and gravel.
• A river constantly picks up and drops sediment
throughout its length.
– Where the river flows quickly, more particles are
picked up than dropped.
– Where the river flows slowly, more particles are
dropped than picked up
• Areas where more particles are dropped are
called alluvial or flood plains, and the dropped
particles are called alluvium.
• Alluvium often contains valuable ores such as
gold and platinum as well as a wide variety of
• Such concentrations of valuable ores are
termed a placer deposit.
• Stream flows that occurs in humid climates
are distributed into fan shaped landforms
called alluvial fans.
• Alluvial soils are finely layered and deep.
• The alluvial sands found close to river banks
and on natural levees are sandier, but can be
more clayey or peaty when close to swampy
• Some alluvial deposits have rich top soil and
are very fertile allowing for the area to be a
• Colluvial deposits are materials that are
moved down slope by gravity and/or erosion
and collect at the base of mountains or
foothills with little or no sorting. (Soils from
colluvial deposition are deep and hard, clay
soils are more common).
• Eolian desert deposits are found in arid
regions around the world.
• Dry air masses create wind systems that
transport then deposit sediment.
• Silt particles, called loess, are carried by the
wind and collect around the fringes of the
• Large areas of the desert environment that
have more than 125 square kilometers of
eoloan sands are called sand seas or ergs.
• Smaller areas are called dune fields
• Variable wind directions and wind force
transport and deposit sand creating different
types of dunes.
• Some dunes are shaped by the wind into
ridges, strings, domes, stars, or half-moon
• Desert consist mainly of wind-deposited sand
that originated from sandstone that has
eroded over time.
• Glacial deposits can move huge amounts pf
soil and bedrock.
• Over 10,000 years ago glaciers extended into
lower latitudes and elevations than in the
• The climate became warmer and these
glaciers began to melt and wear away the
bedrock below the glaciers.
Rate of Glacier Melts
• Different rates of ice melt caused the eroded
sediment to fall out of the retreating glaciers.
• This glacier till formed deposits called
moraines and drumlins.
• The melt-waters flowing in around the
margins of the glacier accumulated deposits
known as outwash plains and depressions
(kettles), small mound shaped accumulation
of sand or gravel called kames, and eskers
(narrow ridges of sediment).
• Loess deposits are commonly located in or
near glacial regions but can also be found in
the desert regions of the world.
• These deposits are composed mainly of silt
grains, with less significant amounts of clay
• Mineral quartz is dominant in loess with
feldspar, carbonates and clay minerals in
• Depending on the type of region where the
loess is found, there will be varying types of
minerals, rocks and sediments.
• Outwash is transported to floodplains by
rivers that drained form glacier melt-water.
• These outwashes are composed of sand, silt
• This debris becomes airborne by strong winds
because there is very little vegetation to hold
the sediment down.
• These loess can be suspended several
kilometers high and travel hundreds of
kilometers in distance.
• Marine deposits mainly rework and distribute
carbonate materials forming ooids on the
• Moderate water circulation on the marine
shelf brings nutrients from deep water to
shallow water that aids in organic growth of
ooids that eventually become cemented
• Waves move the fine carbonate mud and
coarser sediment to form sand and gravel
covered tidal flats, beaches, dunes, marshes,
lagoons and swamps.
• The waves can also move these sediments
towards the sea forming spits, tidal deltas as
well as bar and barrier islands.
• The pounding waves against the shore also
contribute to rock particles and sediment on
the coastal shelf.
• Reefs can be characterized as either thick
masses of living carbonate “rock” or structures
produced by sediment-binding, live
• Other marine depositional environments
• Estuarine deposits consist of cross bedded
sands and mud, or a mixture of both sand and
• Lagoonal deposits include evaporites, fine
grained sediments and black shale.
• Delta deposits and tidal flat deposits contain
primarily mud in the upper zone, mud and
sand in the middle zone and sand in the lower