IH the major 原因 of Landslide

English:
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 acting on an over steepened slope is the primary reason for a landslide, there are other contributing factors affecting the original slope stability:
1.erosion by rivers, glaciers, or ocean waves create oversteepened slopes
2.rock and soil slopes are weakened through saturation by snowmelt or heavy rains
3.earthquakes create stresses that make weak slopes fail (see liquefaction, Hope Slide)
4.volcanic eruptions produce loose ash deposits, heavy rain, and debris flows.
5.vibrations from machinery, traffic, blasting and even thunder may trigger failure of weak slopes
6.excess weight from accumulation of rain or snow, stockpiling of rock or ore, from waste piles, or from man-made structures may stress weak slopes to failure and other structures
7.groundwater pressure acting to destabilise the slope
8.in shallow soils, the removal of deep-rooted vegetation that binds the colluvium to bedrock
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 follow:

• 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 regolithe 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. 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 mass which goes downwards and is 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 like 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".

2007-03-02 19:53:01 補充：
山泥傾瀉（landslide ）:1)當岩層上部為透水層，下部為不透水層時，則不透水層頂部易於聚水，容易使上部岩層下滑。2)強烈風化或鬆散的岩層、斷層面、節理面及岩石層面等天然軟弱面，容易下滑。3)地下水和坡面地表水浸濕斜坡物質。斜坡物質被浸濕後，一方面會軟化，可塑性增強，4)黏著力和摩擦力降低，產生了潤滑作用；另一方面，岩層或土層含水，也增加了重量和動力。5)坡面植被，因自然或人為因素（如斬伐、開田）而被清除或變得稀疏，水分容易滲入土層積聚。6)坡腳被自然或人為因素掏蝕，山坡下部變陡或失去支撐而變成不穩定，上部塊體容易下滑。