Weathering and Mass Movements Chapter 5 Weathering and Mass Movements

5.1 Weathering Mechanical Weathering  Mechanical weathering occurs when physical forces break rock into smaller and smaller pieces without changing the rock’s mineral composition.  In nature three physical process are especially important causes of weathering: frost wedging, unloading, and biological activity.

5.1 Weathering Mechanical Weathering 1. Frost wedging The mechanical breakup of rock caused by the expansion of freezing water in cracks and crevices Sections of rock that are wedged loose may tumble into large piles called talus, which typically form at the base of steep, rocky cliffs.

Frost Wedging

5.1 Weathering Mechanical Weathering 2. Unloading Reduced pressure on igneous rock causes it to expand and allows slabs of outer rock to break off in layers in a process called exfoliation. 3. Biological activity The activity of organisms, including plants, burrowing animals, and humans.

Unloading and Exfoliation of Igneous Rocks

Weathering and Biological Activity

5.1 Weathering Chemical Weathering  Chemical weathering is the transformation of rock into one or more new compounds.  Spheroidal Weathering • Causes the corners and edges of rock to be more rounded

Spheroidal Weathering

5.1 Weathering Rate of Weathering  Two other factors affecting the rate of weathering are rock characteristics and climate. 1. Rock characteristics Mineral composition and solubility

5.1 Weathering Rate of Weathering 2. Climate • Temperature and moisture are the most crucial factors. • Chemical weathering is most effective in areas with high temperatures and abundant moisture.

Erosion The movement of sediments from one place to another

Four Agents of Erosion 1. Water  Most common of the agents of erosion, water moves sediment on Earth than anything else Most sediment is moved by water in lakes, rivers, and streams Third strongest force to move sediment Landforms that will be made from this movement of sediments will be mountains into hills and valleys

Agents of Erosion continued 2. Wind Will pick up many small sediments, but there is not a high enough velocity of wind that will pick up large boulders Winds that will pick up larger sediments would be found in sandstorms and hurricanes Fourth strongest force to pick up and move sediment Landforms that are made from wind moving sediments will form structures like sand dunes

Agents of Erosion continued 3. Ice When large sections of ice called glaciers move across the land, the rocks that they move over will be picked up by the ice and carried as the ice moves Ice will pick up the larger sediments and move them hundreds to thousands of mile Second strongest force to move sediments Landforms that are made from these glaciers of ice moving the sediments are sharp mountains and deep valleys

Agents of Erosion continued 4. Gravity If a rock is broken off something, gravity is the force that is moving it then. Gravity will move the largest of sediments because all objects on Earth are subject to gravity pulling towards the center of the Earth Strongest force to move sediments Landforms that are made when gravity pulls a rock off are called cliffs

Sometimes, humans are considered erosional agents because of all of the construction that occurs all over the planet. In this case, an erosional agent has to be a force of natural origins. >Erosion rates on Earth have increased with the active storms and high energy hurricanes/tornados that have been getting large due to increased temperatures from global warming

Erosion: V-shaped valley is caused by running water

Erosion: U-shaped valley is caused by glaciers

5.3 Mass Movements Triggers of Mass Movements  The transfer of rock and soil downslope due to gravity is called mass movement.  Among the factors that commonly trigger mass movements are saturation of surface materials with water, oversteepening of slopes, removal of vegetation, and earthquakes.

5.3 Mass Movements Types of Mass Movements  Geologists classify mass movements based on the kind of material that moves, how it moves, and the speed of movement.