Chapter 3 – Erosion and Deposition
Section 1 - Wearing Down and Building Up
Erosion – process by which natural forces move weathered rock and soil from one
place to another
 Landslide
 Gravity
 Running Water
 Glaciers
 Waves
 Wind
Sediment – material moved by erosion
Deposition – when the agents of erosion lay down the sediment
Deposition
Weathering
Erosion
Mass Movement
Gravity – the force that moves rock and other materials downhill
Causes Mass Movement
 Landslides
 Mudslides
 Slump
 Creep
Landslides – rock and soil slide quickly down a steep slope
Mudflow – rapid downhill movement of a mixture of water, rock and soil
(water can be as high as 60%)
Clay soil can turn to liquid quickly
Slump – mass of rock and soil suddenly slips down a slope – in ONE LARGE
MASS – often when the base of the soil is rich in clay
Creep – very slow downhill movement of rock and soil. It’s so slow that you
can barely notice it. Can tilt objects. Often from freezing and thawing.
Section 2 – Water Erosion
Runoff and Erosion
Moving water is the major agent of the erosion that has shaped Earth’s land
surface
Runoff – the remaining water that moves over Earth’s surface.
Sheet Erosion – when runoff flows in a thin layer
Rills and Gullies
Rills – tiny grooves in the soil made by runoff
Gully – a large groove or channel in the soil that carries runoff –
rills running together – flow only after it rains
Streams and Rivers
Stream – a large channel formed by gullies running together (creeks or
brooks)
River – streams running together
Amount of Runoff – depends on 5 factors
1. amount of rain an area receives
2. vegetation
3. type of soil
4. shape of the land
5. how people use the land
River Systems
Tributary – stream that flows into a larger stream
Drainage basin – land area from which a river and its tributaries collect their
water.
Divide – the high ground between two drainage basins
Erosion by Rivers
Creates:
Valleys
Waterfalls
Flood plains
Meanders
Oxbow lakes
Flood plain – flat, wide area of land along a river
Meander – a looplike bend in the course of a river
Oxbow lake – a meander that has been cut off
Deposits by Rivers
Deposition creates landforms such as alluvial fans and deltas
Deposition can add to a river’s flood plain.
Alluvial fan – a wide, sloping deposit of sediment formed where a stream
leaves a mountain range. Deposit is shaped like a fan.
Deltas - sediment deposited where a river flows into the ocean – variety of
shapes
Soil of the flood plains – deposition of new soil on the flood plain makes it
fertile for forests and crops.
Groundwater Erosion and Deposition
Groundwater – underground water
Causes chemical weathering – combines with carbon dioxide to form
carbonic acid. Breaks down limestone. Hollows out pockets and eventually can
become a cavern or cave.
Action of carbonic acid results in deposition.
Stalactites – from the roof
Stalagmites – from the floor
Karst Topography –land where there is a layer of limestone and has features
of caves and valleys.
Section 3 – The force of Moving Water
Work and Energy
Energy – the ability to do work or cause change
Potential energy – stored and waiting to be used later
Kinetic energy – energy an object has due to its motion
Potential energy changes to kinetic as gravity pulls water down a slope
How Water Erodes and Carries Sediment
 Sediment comes from mass movement and runoff
 Sediment comes from the bottom or sides of a river
 Wind can drop sediment into the water
Abrasion - wearing away of rock by a grinding action
Load – amount of sediment that a river carries
Ways sediment is carried in a river
 Solution
 Suspended
 Moving along the bed - Rolled along or bounced
Erosion and Sediment Load
What affects how fast the river flows and how much sediment is can erode.
 River’s slope
 River’s volume of flow
 River’s shape of the streambed
Slope – the amount a river drops toward sea level over a given distance
Volume of flow – volume of water that moves past a point on the river in a
given time
Streambed shape – affects the amount of friction
Turbulence –roughness from boulders and other obstacles in the river that
increases friction and reduces the river’s speed.
Shape affects deposition.
Straight rivers – deposition along sides - slowest
Curved rivers – deposition on the inside curve where it is slowest
Section 4 – Glaciers
Kinds of Glaciers
Glacier – any large mass of ice that moves slowly over land
Valley glacier – long narrow glaciers that forms when snow an ice build up
high in a mountain valley
Continental glacier - covers much of a continent
10% of earth’s land
Ice Ages
When continental glaciers covered large parts of earth’s surface
How Glaciers Form and Move
Form in areas where more snow falls than melts
Snow on the bottom compacted into ice
Gravity starts to pull the glacier downhill
Valley glaciers can slide down more quickly – SURGE (one direction)
Continental glaciers (all directions)
Glacial Erosion
Processes:
Plucking – breaking up of rocks and taking them with it
Abrasion – from the rocks
Glacial Deposition
When the glacier melts, it deposits the sediment it carried to create various
landforms.
 Till- sediments deposited directly on the surface.
 Moraine – ridge of till at the farthest point reached by a glacier
 Prairie Potholes – shallow depressions in till that were formed by flowing
water as the glacier melted.
 Kettles – made by retreating glaciers – small depression that forms when a
chunk of ice is left in glacial till.
Section 5 – Waves
Energy comes from wind that blows across the water’s surface
Erosion by Waves
 Impact – hitting with force
 Abrasion – wave carries bits of sand and gravel that wears away rock when
it hits land.
 Change in direction causes a drag on the bottom. Energy concentrated on
headlands (part of a shore that sticks out in the ocean). Over time wears
away the headlands
Landforms Created by Wave Erosion
 Sea caves –
 Wave-cut cliff
 Sea Arch
 Sea Stack
Deposits by Waves - Waves shape the coast through erosion and deposition.
Forming of a beach – an area of wave washed sediment along a coast
Usually Sand
Can be coral or sea shells
Longshore Drift – process where waves hit the beach, and some of the
sediment moves down the beach with the current.
Spit – result of a longshore drift. Beach that projects like a finger out into
the water. Form from deposition of longshore drifts.
Barrier Beach – similar to a sandbar but forms when storm waves pile up
sand above sea level.
Section 6 – Wind
Sand dune – deposit of wind blown sand
How wind causes Erosion
Deflation – process by which wind removes surface materials.
Deposits resulting from Wind Erosion
Sand Dunes
Many shapes and sizes
Loess – fine, wind – deposited sediment
Helps to form fertile soil