1. Learning Objectives
I can identify & explain some of the mass movements that break down materials.
I can summarize the agents of erosion.
I can identify two important factors that affect erosion in a given region.

2. Ch.12, Sec.3 – Mass Movements & Erosion
- weathered rock materials do not stay in place because wherever the ground slopes, gravity causes soil & rock fragments to fall, slide, or move at slow speeds to lower levels
- rain or wind may remove sand & dust from the side of a hill, and a river transports weathered material downstream
- mass movement refers to the downward transportation of weathered materials by gravity
- erosion is the removal and transport of materials by natural agents such as wind & running water

3. Ch.12, Sec.3 – Mass Movements & Erosion
- geologists use the term talus to refer to rock fragments that have been weathered from a cliff and pulled down by gravity
- the movement of a mass of bedrock or loose soil and rock down the slope of a hill, mountain, or cliff is called a landslide
- landslides occur on steep slopes after heavy rains or after snow has melted

4. Ch.12, Sec.3 – Mass Movements & Erosion
Landslide in Keelung, Taiwan in 2010
4 people lost their lives

5. Ch.12, Sec.3 – Mass Movements & Erosion
- there are four different types of landslides: creep, slump, earthflow, & mudflow
- a creep is a very slow movement of soil down a slope (usually made worse by the presence of water)
- a slump is a block of land that tilts and moves downhill along a surface that curves into the slope
creep

6. Ch.12, Sec.3 – Mass Movements & Erosion
slump

7. Ch.12, Sec.3 – Mass Movements & Erosion
- an earthflow is a mass of weathered material that has been saturated with water and flows downhill
- the downhill movement is slower and less fluid than a mudflow
earthflow
earthflow in Colorado

8. Ch.12, Sec.3 – Mass Movements & Erosion

9. Ch.12, Sec.3 – Mass Movements & Erosion
- a mudflow is the rapid movement of water that contains large amounts of suspended clay and silt
- mudflows have much more water than earthflows
- mudflows that follow volcanic eruptions are called lahars
mudflow
lahar

10. Ch.12, Sec.3 – Mass Movements & Erosion

11. Ch.12, Sec.3 – Mass Movements & Erosion
Erosion and Landforms
- rivers, streams, glaciers, wind, ocean waves & currents are all agents of erosion
- rates of erosion in a given region is based upon these agents, climate, and the composition of rocks
- rates of erosion vary based upon the elevation and topography of a region: erosion is greater than uplift in the Appalachians, whereas uplift is greater than erosion in the Himalayas

12. Ch.12, Sec.3 – Mass Movements & Erosion
- regions with humid climates (water is the primary agent of erosion) tend to have a more rounded topography
- regions with dry climates (wind is the primary agent of erosion) tend to have sharp and jagged topography
- some rocks are very resistant to erosion, like volcanic necks which are made of dense, hardened igneous rock
Agaltha Peak in Arizona

13. Ch.12, Sec.3 – Mass Movements & Erosion