Glossary

A volcanic mudflow composed of fragmented material and water, that may be triggered by torrential rain, snow melt or crater lake breaching or overspill.

A landslide is a geological phenomenon that incorporates a wide range of ground movement including 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:

- erosion by rivers, glaciers, or 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

- volcanic eruptions produce loose ash deposits, heavy rain, and debris flows.

- vibrations from machinery, traffic, blasting and even thunder may trigger failure of weak slopes

- 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

- groundwater pressure

- in shallow soils, the removal of deep-rooted vegetation that binds the colluvium to bedrock.

A mudslide (sometimes called a mudflow) is the most rapid (up to 80 km/h) and fluid type of downhill mass movement comprising of at least 50 per cent silt and clay-sized materials and up to 30 per cent water.

An avalanche is a very large slide of snow down a mountainside, caused by the release of accumulated snow down a slope, and is one of the major dangers faced in the mountains in winter. The potential for a snow slope to fail depends on a range of factors including the terrain (steepness, direction, profile and surface of a slope), structure of the snowpack (compacted snow is less likely to move than powdery snow), solar radiation, temperature, wind and snowfall amount.