Name ______Period ______Date ______

Ch.8 Erosional Forces

Section 1: Erosion by Gravity

Erosion- a process that wears away surface materials and moves them from one place to another

Deposition- the relocation of sediments

Mass Movement (4 Types)

  1. Slump- soil and rock slip down slope as one large mass or break into several sections
  1. Creep- occurs when sediments slowly shift their position downhill

Ex: leaning trees and human build structures

  • Common in areas of frequent freezing and thawing
  1. Rockfalls/rock slides- blocks of rock break loose from a steep slope and tumble downhill
  • Common in areas of freezing and thawing
  1. Mudflows– a thick mixture of sediments and water flowing down a slope
  • Usually occurs in areas that have thick layers of loose sediments

Slump, creep, rockfalls, and mudflows all have 3 things in common:

  1. They are all most likely to occur on steep slops
  2. They all depend on gravity to make them happen
  3. They occur more often after a heavyrainfall

There are 3 ways to help Make Steep Slopes Safe:

  1. Plant vegetation
  2. Drainage pipes or tiles inserted into the side of a slope
  3. Build walls of concrete or boulders

Section 2: Glaciers

Glacier- a large mass of ice and snow moving on land under its own weight

Plucking- occurs when glacial ice melts, water flows into cracks in rocks. Later, the water freezes in the cracks, expands, and fractures the rock. Pieces of the rock are then lifted out by the ice.

  • This process is very similar to the mechanical weathering process ice wedging.

How can we tell which direction the glacier moved? By looking at the grooves and striations

Ice Depositing Sediments

What is the term used when a glacier starts to melt and shrink? “Retreat”

  1. Till- A mixture of different sized sediments left behind by a melting (retreating) glacier
  • Some till deposits are so large they can fill in valleysand make them appear flat.
  1. Moraine Deposits- When rocks and soil are moved to the end of the glacier, a big ridge of material piles up.

(These long, dark lines on the Aletsch glacier in Switzerland are examples of medial and lateral moraines.)

  1. Outwash Deposits- material deposited by the melted water from a glacier, most often beyond the end of the glacier
  • This process can sometimes form a fan-shaped deposit
  1. Eskers- Fig 12 refers to eskers as glacial deposits formed by melting water

Continental Glaciers

Continental glaciers cover 10% of Earth.

Climate Changes:

  • In the past, continental glaciers covered about 28% of Earth
  • The average air temp. on Earth was about 5˚C lower during these ice ages

Valley Glaciers

What do you look for to determine if valley glaciers existed in a particular mountain?

  1. Striations
  2. Plucking
  3. Bowl-shaped basins called cirques are eroded into the sides of the mountains
  4. If 2 valley glaciers side by side erode a mountain, a long ridge called an arête will form between them
  1. If valley glaciers erode a mountain from several directions, a sharp peak called a horn will form.

(The Matterhorn in Switzerland is the most famous example of this type of erosion)

  1. Stream eroded valleys are V-shaped. Glacially eroded valleys are U-shaped.

(This valley in Glacier National Park shows the characteristic 'U' shape of a glacially carved valley.)

Give 2 reasons why glaciers are and have been important to the Earth’s surface

______

Section 3: Wind

Deflation- when wind blows across loose sediments, removing small particles such as silt and sand

Abrasion- the process occurs when windblown sediment strikes rock, the surface of the rock gets scraped and worn away

  • Similar to sandblasting

Deflation and abrasion happen to all land surfaces, but occurs mostly in deserts, beaches, and plowed fields due to the lack of plants.