The Earth’s Crust Weathering & Erosion

Soil begins with rocks – so how is rock turned into soil? How does soil travel and move?

Inside the Earth The Earth's Crust is like the skin of an apple. It is very thin in comparison to the other three layers. The crust is only about 3-5 miles (8 kilometers) thick under the oceans(oceanic crust) and about 25 miles (32 kilometers) thick under the continents (continental crust). The temperatures of the crust vary from air temperature on top to about 1600 degrees Fahrenheit (870 degrees Celcius) in the deepest parts of the crust

Weathering & Erosion Weathering – a natural process that breaks down and wears away rocks to create sediments Erosion is the movement of small rock particles by wind, water and ice

There are three kinds of weathering: 1. Mechanical 2. Chemical 3. Biological

Mechanical Weathering– the physical break up of rocks.

Examples Gravity – pulls rocks down cliffs and mountains smashing them

Moments before this rock fell, it was one large rock Moments before this rock fell, it was one large rock. How many pieces of rock do you think there are now?

ICE– the freezing and thawing of water within cracks in rocks

Freeze-Thaw Action

What do you think will happen to this rock when it falls?

This rock froze and thawed so many times that it slowly burst from the strain.

Erosion– wind, water, and ice wear away at the surfaces of rock and carry the pieces to another spot. E.g. dust storms, rivers, glaciers, ocean waves

Mass Movement Mass movement means the movement of any loose material (rocks, soil, mud) down slope under the influence of gravity. The loose material is known as regolith. The rate of mass movement is influenced by 4 factors. Gradient Water Content Human Activity Vegetation

Influences on Mass Movement Gradient – Mass movement occurs on sloping land. Mass movement is fastest on steep slopes. Water Content – After heavy rain the regolith (loose material) is heavier. Human Activity – People often cut into hillsides to make roads or railway lines. This creates steep slopes where mass movement can occur. Vegetation – The roots of trees and plants help keep the regolith together, slowing down mass movement.

Speed – Slow Speed – Fast Types of Mass Movement There are different types of mass movement. They are grouped according to the speed at which they occur. Types of Mass Movement Speed – Slow Speed – Fast 1. Soil Creep 1. Landslides 2. Bog bursts 3. Mudflows

Soil Creep

Soil Creep

Landslides

Mudflows

Chemical Weathering– the breakdown of rocks by water, chemicals, and gasses Chemical reactions can speed up the process of erosion – e.g. acid rain. Acid rain dissolves minerals found in rock which weakens the entire rock making it easier to break. It occurs because rainwater mixes with carbon dioxide in the atmosphere, forming a weak carbonic acid.

A Karst Limestone Pavement

3. Biological Weathering – the breakdown of rock by living organisms (plants, fungi, and bacteria)

The roots of plants can work their way into the cracks of rocks and widen them while other plants and animals produce chemicals that can erode rock.

These lichen are beginning to break down this rock – the first step in a long process of creating soil. How long do you think it takes for soil to form from solid rock?

Even these mushrooms break down rock – they secrete digestive juices onto the forest floor and then absorb the nutrients – the acids also inadvertently dissolve small rocks.