Landslide's+History

= = =~LANDSLIDE HISTORY~=

A **landslide** is a geological phenomenon which includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows. Although gravity's action on an over-steepened slope is the primary reason for a landslide, there are other contributing factors affecting the original slope stability: In order to clarify the meaning of the word "landslide", the main points of agreement among various authors in the terminological definitions of landslide events can be summarised as follows: • Landslides represent one category of phenomena included under the general heading of mass movements. The term therefore describes a movement of a mass of rocks or soil from a higher point to a lower one. • Gravity is the principal force involved. The movement of the masses is due to the action of the force of gravity, but other forces like those due to earthquake or due to water filtration can be involved. • Movement must be moderately rapid. Creep that affects the regolith without definition of the sliding surface is therefore a slope movement but is not a landslide. • Movements may include falling, sliding and flowing. The first is the movement of masses or blocks in free fall; the second is the movement along more or less well-defined surfaces, the third, is movements of masses in a fluid-plastic or viscous state. • The plane or zone of movement is not identical with a fault. A fault can be a part of a sliding surface. • Movements should be downwards and outwards with a free face, thus excluding subsidence. Subsidence is a mass movement, in which a mass goes downwards induced by gravity and/or specific water conditions. • The displaced material has well-defined boundaries and usually involves only limited portions of the hillside. This shows that a landslide movement always involves a volume of material whose limits can be recognised or approximated and whose determination is at the basis of the identification of the mechanism movements. • The displaced material may include parts of the regolithe and/or bedrock. The materials involved can therefore be rocks at various levels of alteration or the product of disgregation phenomena in the past. • Frozen ground phenomena are usually excluded. Therefore solifluction due to frozen ground phenomena such as creep, can be classified as slope movement but is not a landslide. • On the basis of what is stated above, a complete definition of a landslide event could be the following: "Movement of soil or rock controlled by gravity, superficial or deep, with movement from slow to rapid, but not very slow, which involves materials which make up a mass that is a portion of the slope or the slope itself". 1181786109Soraya Yousefi
 * Natural Causes:**
 * erosion by rivers
 * glaciers melting
 * ocean waves create oversteepened slopes
 * rock and soil slopes are weakened through saturation by snowmelt or heavy rains
 * earthquakes create stresses that make weak slopes fail (see liquefaction, Hope Slide)
 * volcanic eruptions produce loose ash deposits, heavy rain, and debris flows.
 * thunder may trigger failure of weak slopes
 * excess weight from accumulation of rain or snow
 * groundwater pressure acting to destabilise the slope
 * Human Causes:**
 * vibrations from machinery
 * traffic and road construction
 * blasting
 * stockpiling of rock or ore, from waste piles, or from man-made structures may stress weak slopes to failure and other structures
 * in shallow soils, the removal of deep-rooted vegetation that binds the colluvium to bedrock
 * Mining
 * Logging
 * Overgrazing

Landslides occur and can cause damage in all 50 States. Severe storms, earthquakes, volcanic activity, coastal wave attack, and wildfires can cause widespread slope instability. Landslide danger may be high even as emergency personnel are providing rescue and recovery services.

To address landslide hazards, several questions must be considered: Where and when will landslides occur? How big will the landslides be? How fast and how far will they move? What areas will the landslides affect or damage? How frequently do landslides occur in a given area?

Answers to these questions are needed to make accurate landslide hazard maps and forecasts of landslide occurrence, and to provide information on how to avoid or mitigate landslide impacts. 1181153426Soraya Yousefi

= = Landslides cause $1-2 billion in damages and more than 25 fatalities on average each year. A landslide is a geological phenomenon which includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows. They can occur on any terrain given the right conditions of soil, moisture, and the angle of slope. 1179243209

Landslides that have happened over the years!!! [|La Conchita]

When- The 2005 La Conchita landslide occurred at about 12:30 p.m. on January 10. Where- Lacinchita happened in the gated (private) community of La conchita. How- It happened beccause of all the rain that had fell the night before. [|Some more info] La conchita was a huge surprise to the community of La conchita. It was a huge disaster. it caused a lot of damage both emotionaly and meatiraly. From December 27, 2004 through January 10, 2005, Ventura received 378 mm (14.9 in) of rainfall, only slightly less than its avarage annual total of 390 mm (15.4 in). The rain soaked into the hilside of La conchita.\
 * - [|BILLYBOBNORTON]** [[image:http://www.wikispaces.com/user/pic/BILLYBOBNORTON-sm.jpg width="16" height="16"]] May 17, 2007 8:23 am