How Water Shapes the Earth’s Surface
There are 3 processes by which water shapes the Earth’s surface: Weathering and erosion are the 2 main processes by which water breaks down Earth’s landscapes. Deposition is the process by which water builds up features in the landscape.
A. Weathering = the gradual process of breaking rock down into smaller pieces Sediment = rock that has been broken down into tiny pieces Weathering can take thousands of years There are 3 main kinds of weathering:
Physical Weathering – rock is broken down physically without changing its composition
Eg: frost wedging - water gets into cracks in rock, freezes and expands, breaking the rock apart.
Chemical Weathering - the minerals in rock react with chemicals in the environment such as oxygen, carbon dioxide, water and acids
Biological Weathering – physical or chemical weathering caused by plants or animals
Example: plants such as lichen release chemicals that slowly dissolve the rock they grow on
B. Erosion = pieces of weathered rock are transported away from their original location Erosion is said to “carve” the landscape. Erosion can be fast or slow There are 4 main transporters (called “agents of erosion”):
Water - running water carries sediment away.
eg: Rivers in mountainous areas carve steep valleys that have a V-shape.
Wind - strong winds can carry exposed soil away
Gravity - mountains gradually crumble as gravity pulls rocks down.
The sudden rapid movement of rock material down a mountain is called an landslide.
Ice - glaciers carry rocks and boulders with them when they move, then drop them when they melt.
Weathering and Erosion Create Caves
Caves are created by chemical weathering of underground limestone rocks (made of calcium carbonate), Water and carbon dioxide in the air combine to form a weak acid which seeps into the ground and slowly dissolves the rock over thousands of years. underground streams transport the dissolved rock away, leaving a hollow space
When a cave forms close to the surface, a sinkhole may form.
A landscape with many caves and sinkholes is called a Karst
How Glaciers Shape the Landscape
When glaciers move, they leave scratch marks (called “striations”) on the rock
Glaciers are so huge that they can carve out whole valleys Glaciers are so huge that they can carve out whole valleys. These valleys have a U-shape.
A hanging valley is a small U-shaped valley cut off by a bigger valley created by a bigger glacier
A cirque is a bowl-shaped valley at the head of a glacier
An arete is a narrow ridge between two cirques
A horn is a pyramid-shaped peak between three cirques
A fjord is a narrow ocean inlet carved by a glacier
The Effects of Global Warming on Glaciers: All over the planet, glacier have “receded” (shrunk) in the past 100 years.
Mount Kilimanjaro in 1993...
... and in 2000.
Mount Kilimanjaro in 1993...
... and in 2000.
McCall Glacier in 1958... McCall Glacier from July of 1958
... and in 2003 McCall Glacier August 13, 2003
C. Deposition = eroded sediments and other materials are deposited by water or ice, building up the landscape.
A delta is an area of built-up sediment dropped when a river empties into an ocean or a lake. It is usually triangular or fan-shaped.
A moraine is a ridge of rocky material left by a glacier The terminus of Mendenhall Glacier. Ice absorbs all wavelengths except blue.
An erratic is a large boulder left behind by a glacier.