Download Erosion and Sedimentation

Erosion and Deposition
Grinding down and washing away
What is sediment? (notes)
• Sediment is a naturally occurring material
that has been broken down.
• Common examples would be clay, peat, and sand
Betsiboka River,
Madagascar
What is erosion? (notes)
• Erosion is the process of moving
sediment from one location to another.
• The most important force that powers
erosion is gravity.
• However, there are many different agents
that directly cause the erosion.
Newton and his amazing gravity
Sometimes erosion takes us by surprise
What is deposition? (notes)
• Deposition (“to deposit”) is the dropping off of sediment
• The size, density, and shape of the particles affect how fast deposition
occurs.
Particle sizes
Particle shapes
Agents of Erosion (not notes)
• Each agent we discuss will have certain properties to the sediment
that it creates.
• The two main points will be:
• The general appearance of the sediment produced.
• Whether the sediment is sorted or unsorted.
Agents of SHIELD Erosion
Agents of Erosion – Water (notes)
• The most common and powerful agent of erosion.
• Sediment appears rounded and smooth
• Sediment is sorted
Water – Sorting (not notes)
• Running water starts with a
whole mixture of materials in it at
the beginning.
• But as it flows the biggest rocks
drop out first, followed by the
smaller ones, and finally the very
smallest particles fall out.
• This sorts the material along the
path of the river.
Boulders
Cobbles
Gravel
Sand
Silt
Clay
Water – Movement of Particles (notes)
• Suspension is when particles that are of low size and density are
picked up and carried by the water.
• Saltation is when particles that are of medium size and density
bounce along the river bottom.
• Rolling is when large particles (“rocks”) are pushed along the bottom
of the river.
Water – River Structure (not notes)
• When rivers flow across an open area they
begin to meander (curve).
• This is because where the river flows faster on
the outer bank it wears away at the bank.
• Where the river flows slower on the inner
bank it drops off sediment.
• In extreme cases the river bends so far that
the tip breaks off and forms an “oxbow lake”.
Oxbow lakes beginning to form in Sandakan, Malaysia
An oxbow lake on the Danube River
Water – Waterfalls (not notes)
• Waterfalls occur when a hard layer of rock is on top of a softer layer.
Agents of Erosion – Ice (notes)
• Glaciers are massive sheets of ice that move slowly along the land.
• Glaciers are the only erosive force that can transport large boulders.
• Sediment appears scratched
and grooved
• Sediment is completely unsorted
Glacial “till”
Boulder in Madison, New Hampshire, that was transported by a glacier
Ice – Sorting (not notes)
• As glaciers grind along they pick up rocks of
various sizes.
• However, when it becomes warmer the
glacier melts and drops all of them in a big
pile.
Valley Shape (notes)
• You can tell what formed a valley depending on its shape.
A U-shaped valley is formed by a glacier
because the ice squashes out and flattens
the bottom.
A V-shaped valley is formed by running
water as it cuts down through the layers.
Agents of Erosion – Wind (notes)
• Wind can only transport very small particles.
• Sediment appearance is…well…small.
• Sediment is sorted (same reason
water sorting occurs)
Wind – Shaping the Land (not notes)
Even though it can only move small
particles, given time it can wear
away a large volume of rock.
Agents of Erosion – Gravity (notes)
• Gravity can act as a direct agent as well as the force that drives
erosion.
• Sediment appears jagged and angular
• Sediment is unsorted (same reason
that glaciers are unsorted)
(Rocks fall; aren’t you glad you came to school to learn this?) ->