Mudslides and Landslides Dangerous Earth Movements

Introduction

"Mudslide, also called a landslide or a land slip. It is a downward mass movement of earth or rock on unstable slopes, including many forms resulting from differences in rock structure, coherence of material involved, degree of slope, amount of included water, extent of natural or artificial undercutting at the base of the slope, relative rate of movement, and relative quantity of material involved. Many terms cover these variations; creep, earthflow, mudflow, solifluction, and debris avalanche are related forms in which mass movement is by flowage. If shearing movement occurs on a surface on consolidated rock, the dislocated mass is a debris slide. Cliffs may become so steepened through undercutting by rivers, glaciers, or waves that masses of rock will fall freely and constitute rock fall type of mudslide"(Britannica, 1985).

[Photo Complements of the National Landslide Information Center, U.S. Geological Survey

Geologic Processes

This picture comes from the U.S.G.S Public Affairs Office Menlo Park, California	Mudslides occur when a portion of a hill side becomes too weak to hold up its own weight. This is generally caused by an entense amount of rain fall. With all of the new water intrduced into the slope the content of liquid makes it so heavy that gravity pulls it downward(Landslides, 2002). Although water plays a major factor in creating the mud that flows in a mudslide the real reason that the land begins to slide is gravity. What happens is mudslides redistribute soil and sediments in a process that can be in abrupt collapses or in slow gradual slides(APA, 2002). Some other factors in causing mudslides are earthquakes, slope faliures, heavy storms. All of the natural causes of mudslides are not nearly as bad as the human made causes such as grading terrain cutting, and excessive development. These factors fall under the external causation of loading and un loading. According to the Royal Academy of Engineering the causation of mudslides can be catorgized into to two groups internal factors and external factors.
This Image comes from Economist, 03/18/2000, Vol. 354 Issue 8162, p43, 1p, 1 map, 1bw   Do you think that these kids are thinking of the angle of repose that they are sliding down? So much devastation is involved with a mudslide, it is nice to see someone actually enjoying the aftermath of a mudslide. Also the only unloading of material in this picture is done by the kids bellies.	I.Geometrical change 1. Gradient 2. Height 3. Slope length II.Unloading 1. Natural 2. Human-induced III.Loading 1. Natural 2. Human-induced IVShocks and Vibrations 1. Single 2. Multiple/continuous Internal V.Progressive failure (internal response to unloading, etc.) 1. Expansion, swelling 2. Fissuring 3. Strain softening 4. Stress concentration VI.Weathering 1. Physical property changes, swelling 2. Chemical changes VII.Seepage Erosion 1. Removal of cements 2. Removal of fines VIII.Water Regime Change 1. Saturation 2. Rise in water table 3. Excess pressures 4. Drawdawn
	This picture shows how over development can cause mudslides that are dangerous. The bank that was cut out for the highway that was cutting through exposed the soil to the process of weathering which is a major cause of slides. The construction unloaded the vegetation and rocks along the side to fit the road in this allowed for the slide to cover the road.

The Geomertrical changes are the main reasons for mudslides changes in the gradient will cause for sediments to loosenes and rocks and debris to start to move. Hieght plays an important role due to the concept of potential enegery what potentional enegery is the higfher that you are the more room that gravity has to pull on you. The slope lenth in cojunction with the hieght gives you the angle of repose this is the angle at which the material will remain stable. If the angle is acted upon by loading or unloading than it is changed and the cliff is no longer stable(Forces of Nature 2 2002).

Products of the Geologic Process

This diagram illustrates the movement of a large chunk of land that is starting to slide. The gravity is pulling it downward at a pretty fast speed. The movement of the block is parallel to the plains of weakness.

Also another type of slide is a flow it travels like lava flowing from a volcano. Some fluid like substance picks up the sediment. The main fluid like substance is water that comes from rainfall. Also like I mentioned lava flows called lahars(What Are Landslides 2002).

This diagram is of a slump, which is another type of slide. This type of slide is due to the amount of water in the soil (APA 2). The water content allows the material to fall or slump down the hill the usually is not very fast.

This type of slide is normally caused by extreme wet weather, human disturbances like roads that have been cut out, also logging. These types of loading and unloading of the soil take away the stability of the slope. If the angle of repose is changed than the slope will not be as stable this may cause slope failures. When the slope fails than anything in its way will be cover and probably destroyed(Puget 2002).

One final type of slide is a Torrent, this normally occurs when an extreme amount of rain falls in a short amount of time. One other form of torrents is lava flows that explode down the slide of cliff. This sudden rush of water creates channel like discharges of water and debris that is carried by the water.

Impacts

Some impacts from landslides can be devastatinging in Southeren Italy last year over 147 people were killed when a landslide tore through the region of Campania in southeren Italy. Over the year s there have been landslide that have killed thousands of people(Ieropoli 1998). I have listed below a list of the top ten deadlist Landslides of all time(Forces of Nature 2002).

Date Location Dead

1920, December 16 Kansu,China Over 180,000
1949 Khait, Tadzhikistan 12,000
1618, Sept. 4 Chiavenna Valley, Itlay 2,240
1966, Jan. 11-13 Rio de Janeiro, Brazil 550
1806, Sept. 2 Goldau Valley, Switzerland 500
1974, April 26 Huancavelica Province, Peru 200 to300
1980, Sept. 8 Darjeeling, India 250
1981, Oct. Sichuan Province, China Over 240
1923, Sept. 1 Nebukawa, Japan 200
1971, March18 Chungar, Peru 200

Literature cited

Puget Sound Department of Ecology 2002 Home page http://www.ecy.wa.gov/programs/sea/landslides/about/about.html
Accessed March 15,2002

Forces of Nature: TQ 2000. Home page. http://library.thinkquest.org/C003603/english/landslides/tenworst.htm Accessed March 19,2002

Forces of Nature 2: TQ 2000. Alternate page on mudslides http://library.thinkquest.org/C003603/english/landslides/tenworst.htm Accessed March 17,2002

Royal Academay of Engineering. 1995 Home page. http:royalacademy/eng/.org Accessed March 16, 2002

USGS science for a changing world. 2002. Hazard fact sheet. http://landslides.usgs.gov/html_files/nlic/page5.html Accessed March 12, 2002

Ieropoli, Rosa. May 21,1998. The Italian government ignored geologist's warnings http:www.wsws.org/news/1998/may/1998/it-21.shtml Accessed March 2, 2002

Grade 7 Natural Disasters Project. Landslides 2002 http:www.germantown.k12.il.us/html/landslides.html Accessed March 1, 2002

APA Research/landslide Hazards and Planning/ The Causes of Landsliding: last updated 2/18/2002. http://www.planning.org/landslides/docs/causes.htm Accessed March 2, 2002

[Links to all class members sites will be inserted here.]

Copyright ©-2001 Earlham College. Revised 25 February 2002. Send corrections or comments to donatru@earlham.edu