Weathering and erosion

What is Weathering? Weathering is

the breaking down of rocks and other materials on the earth’s surface

Two Types of weathering

1. Mechanical/Physical – Breaks rocks into different shapes and smaller pieces.

o There is no change in the rocks chemical composition.

Agents of mechanical weathering

Temperature : Changes in temp. cause repeated expansion and contraction.

Agents of mechanical weathering

Ice Wedging: when liquid water goes into cracks and then freezes causing the cracks to get wider.

A rock in Iceland that has been weathered by the freeze-thaw process.

Agents of Mechanical Weathering

Biological activity (root-pry, burrowing animals, human activities)

Agents of mechanical weathering

Gravity: Rocks falling and colliding with other rocks.

How can gravity cause weathering????

Agents of mechanical weathering

Abrasion: Wearing away by solid particles. Happens when 2

rocks rub together

Wind Blown Sand

Wind abrasion has carved this Double Arch located in Arches National Park

What Happened?

Before After

Agents of mechanical weathering

Unloading: The expanding of high pressure rock when exposed to a lower pressure rock

Sheeted Granite in Yosemite National Park. The granite is broken into gently plates by unloading joints. This happens as the rock is exposed by erosion. These joints provide pathways for water to enter the rock.

Closer to home

These rocks on Stone Mountain have been broken into sheet because of uploading

Chemical weathering

The altering of the composition of minerals within a rock that results in a reduction in size.

Agents of chemical weathering

Water: Dissolves minerals in rocks, making them weaker.

Agents of chemical weathering

Acid: Dissolves minerals in rocks (examples: carbonic acid, acid rain, and plant acid)

Limestone and marble are the most affected types of rocks.

Acidic Water has dissolved the limestone on the statue.

This marble tombstone in New Orleans has been weathering by acid rain.

Lichens, a moss like plant that grows on rocks, can produce weak acids that react with the rock, causing weathering.

Agents of chemical weathering

Oxidation: Oxygen combines with iron minerals and sulfur minerals changing the composition of the rock

Oxidation turned these rocks in Nevada's Valley of Fire red.

Factors that determine the rate of weathering

Composition: What the rock is made of

Physical condition of rock: Cracks, holes, crevices – easier weathering

Solid, unbroken – more weather resistant

Factors that determine the rate of weathering

Climate: Cold Climates: mechanical weathering

breaks down rocks rapidly Warm, wet Climates: chemical weathering

breaks down rocks rapidly Topography:

The position of the rock. Air Pollution:

Amount of time rock was exposed. Surface area that was exposed.

Erosion

The movement of weathered particles from one location to another, where it is deposited.

The 4 main agents of erosion are: Water, Wind, Gravity, and Ice.

Water erosion

Liquid water is the most common type of erosion.

Why? Streams, raindrops, waves

Wind Erosion

Happens mainly in dry, windy climates. Ex: Deserts, the beach (sand dunes)

Ice erosion

Moving ice, in the form of glaciers, changes the surface of the Earth.

Glaciers are the most powerful form of erosion, but the least common.

Gravity erosion

Movement of particles on steep slopes because of the influence of gravity.

Deposition

The process by which material is laid down or dropped.

Water, wind, ice and gravity all move the sediments (erosion).

Eventually, the energy is lost and this movement slows down. When the sediments no longer move, they are deposited.

Objects with more mass will settle faster than objects with less mass.