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

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

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

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

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

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

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

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

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

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

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