What are landslides and how do they occur?

Landslides have always existed on our planet. Generally classified as mass movements of rock, debris, and soil down a slope of land. While landslides are a naturally occurring environmental hazard they have recently increased in frequency in certain areas due to human activity. Although there are many different causes of landslides, they all have two things in common. According to Geoscience Australia's website at http://www.ga.gov.au "...they are the results of the failure of the soil and rock materials that make up the hill-slope and they are driven by gravity."

Natural causes of Landslides:

Earthquakes: Seismic activities have always been a main cause of landslides throughout the world. Any time plate tectonics move the soil that covers them moves with it. When earthquakes occur on areas with steep slopes, many times the soil slips causing landslides. Furthermore, ashen debris flows caused by earthquakes can also trigger mass movement of soil.

Heavy Rainfall: When sloped areas become completely saturated by heavy rainfall many times landslides can occur. Without the aid of mechanical root support the soil simply runs off when it contains too much water.

Human causes of Landslides:

Clear Cutting: Method of timber harvesting which completely removes all old growth timber from the area. This method is hazardous because it destroys the existing mechanical root structure in the area.

Mining: Mining operations that use blasting techniques often cause other areas that are at the risk of sliding to slide due to vibrations under the soil.