Erosional
Forces
Erosion
• Wearing away of surface materials by
gravity, water, wind, or glaciers.
• Deposition- process where sediments are
dropped by erosion agents as they lose
energy.
• Mass movement occurs as gravity moves
materials down a slope as one large mass.
• Examples: Slumping, Creeping, Rock
Falls/Slides, & Mudflows
 Steep slopes can be made safer with
vegetation, drainage pipes, and walls of
concrete or railroad ties.
Glaciers
• Large masses of ice and snow that slowly
move on land causing erosion.
• Plucking- erosion process caused by
moving glaciers picking up boulders, gravel,
& sand.
• Scour & scrape the soil and bedrock.
• Grooves & striations indicate the direction a
glacier moved.
• Glaciers deposit a mixture of different sized
sediments (till) when they retreat.
oMoraine- a ridge, or pile, of deposit left at
the end of a glacier.
oOutwash- material deposited in layers by
the meltwater of a glacier, with largest
pieces closer to the glacier..
oEskers – outwash deposit formed as
meltwater rivers within the ice deposit sand
& gravel within their channels.
Zone of Accumulation
Snowline
Crevasses
Zone of Wastage
• Types of Glaciers
Continental Glaciers-huge masses of ice
and snow that cover large areas of land.
•Covers 10% of Earth near the poles.
(Antarctica & Greenland)
•Ice Ages - periods of widespread
glaciation over the last 2 to 3 million yrs.
•Thicker than some mountain ranges.
 Valley Glaciers- exist in mountain ranges.
• Cirques- bowl-shaped basins in the sides
of mountains.
• Arête- a long ridge that forms when two
valley glaciers erode a mountain side-byside.
• Peaks- form when valley glaciers erode a
mountain from several directions.
• Valleys formed by glaciers are “U” shaped
Wind
• Scatters dust or volcanic ash over
thousands of kilometers.
• Deflation- wind removes small particles of
loose sediment, leaving behind heavier
materials.
• Abrasion- wind behaves like a sandblaster
The rocks wearing
blowing sand grains against
them down.
• Windbreaks – rows of trees planted to slow
down wind in order to reduce erosion.
• Dunes – mounds of sediment drifted by
wind.
Water Erosion
Surface Water
Runoff
• Rainwater that doesn’t soak in to the
ground or evaporate.
• Affected by:
 Amount of rainfall
 Length of time it falls
 Steepness, or slope, of the land
 Amount of vegetation
Rivers & Streams
• River system –network of groundwater &
streams that come together to form a
system.
• Drainage Basin- area of land from which
a stream or river collects runoff.
 The Mississippi River drainage basin is
the largest in the United States
Young River
 Flows swiftly through a narrow
valley.
 May have rapids & waterfalls.
 Erodes the bottom faster than the
sides.
 “V” shaped valleys
Mature Stream
 Flows smoothly through the valley.
 Erodes more on the sides.
 Forms meanders & oxbow lakes.
 Carves a flat, broad valley floor
called a floodplain.
Old Stream
 Flows smoothly through a floodplain it
has carved.
flood plain
meanders
oxbow lake
valley wall
• Delta – fan shaped area formed by sediments
that are deposited as water empties into an
ocean or lake.
• Alluvial Fan – fan shaped area formed by
sediments that are deposited as water
empties from a mountain valley onto a flat
open plain.
Groundwater
• Groundwater is water that soaks into the
ground and collects in the pores of the
underlying soil.
• Soil and rock are permeable if water can
pass through the pore spaces. (Sandstone)
• Soil and rock are impermeable if water can
not pass through the pore spaces. (Granite)
• Aquifer – a layer of permeable rock that
lets water move freely.
 Zone of Saturation : area where all the
pores are filled with water.
 Water Table : upper surface of the zone
of saturation.
Aquifer
Zone of
Aeration
Water Table
Zone of
Saturation
•Wells are used to pump groundwater from an
aquifer to the surface.
Artesian wells – wells that don’t require a
pump because the water is under pressure.
Spring – free flowing water because the
water table is so close to the surface.
Geyser
The – hot spring that erupts
peroidically, shooting water & steam into
the
the air.
• Caverns are formed by Carbonic acid
dissolving limestone rock, thereby enlarging
cracks to form chambers.
Stalactites– Calcium carbonate deposits
that hang from a cave’s ceiling.
Stalagmites – Calcium carbonate deposits
that form on a cave’s floor.
Other Features:
Soda Straws
Columns
Cave Popcorn
Cave Pearls
Draperies
Ocean Shoreline
 Shoreline Forces
– Waves pound
against pound
against shores.
– Currents move
sediments along
the shoreline.
– Tides carry
sediment out to
sea & bring in
new sediment.
 Rocky Shorelines
 Rocks & cliffs
 C. Sandy Beaches
 Beaches –deposits of sediments parallel
to the shore.
 Barrier Islands – fragile sand deposits
that parallel the shore but are separated
from the mainland.