Ch. 8 Sec. 1 Mass Movements
Mass movements alter Earth’s surface over time due to gravity moving sediment and rocks downslope. Review Vocabulary gravity: the force every object exerts on every other object due to their masses
I. Mass Movements - • downslope movement of soil and weathered rock resulting from the force of gravity • Climatic conditions determine the extent • Occurs on slopes • Fine-grained to boulder size
II. Factors that Influence Mass Movements • material’s weight • material’s resistance to sliding or flowing • triggers that shake material loose • the presence of water
III. Types of Mass Movements A. Creep - slow, steady, downhill flow of loose, weathered Earth materials • Usually noticeable only over long periods of time • Solifluction • a. Creep in permafrost areas • b. Mud-like liquid due to melting
One way to way to tell whether creep has occurred is to observe the positions of structures and objects.
B. Flows • Earth flows are moderately slow • Mudflows are swiftly moving • a. Triggered by earthquakes (vibrations) • b. Common near volcanoes (heat melts snow) • c. Also common in sloped, semi-arid regions that experience intense, short-lived rainstorms romania
3. Lahara. Mudflow after volcanic eruption b. Snow and ash Mt. St. Helen
C. Slides • Landslides • a. Rapid, downslope movement • b. Block of soil, rock, and debris separates from the underlying bedrock • c. Common on steep slopes
2. Rockslide - a sheet of rock moves downhill a. Often triggered by earthquakes.
3. Slump a. landslide moves along a curved surface b. Crescent-shaped scars on slope
4.Avalanche a. Landslide that occurs in mountainous areas (slopes of 30o to 45o) b. Thick accumulations of snow c. Occur when snow builds up, becomes heavy, slips off, and slides downslope.
D. Rockfalls • On high cliffs • Rocks loosened by physical weathering • Break up and fall downward • Common at high elevations, in steep road cuts, and on rocky shorelines • Talus Slope
IV. Mass Movements Affect People Human activities such as construction of buildings, roads, and other structures can make slopes unstable, contributing to the factors that cause mass movements. The best way to reduce the number of disasters related to mass movements is to educate people about the problems of building on steep slopes.
Mass movements alter Earth’s surface over time due to gravity moving sediment and rocks downslope. • Mass movements are classified in part by how rapidly they occur.
Factors involved in the mass movement of Earth materials include the material’s weight, its resistance to sliding, the trigger, and the presence of water. • Mass movements are natural processes that can affect human life and activities. • Human activities can increase the potential for the occurrence of mass movements.
What is a lahar? Answer: A lahar is a mudflow that forms on a volcano, often just after an eruption. The presence of loose volcanic ash and snow that can melt rapidly contributes to conditions favorable for the formation of lahars.