Landslides have been occurring as a natural phenomenon since ancient times causing devastation and altering the geographical landscape. It has only been in recent years however that human causes have begun to have an effect on how landslides occur, their frequency and severity. Although there are many causes that have been assessed to be a contributing factor in the causation of landslides there are always two intrinsic factors that are present in all landslides that “are all results of a failure of the soil and rock materials that make up the hill-slope and they are driven by gravity” (Geoscience Australia, 2012). A landslide is defined as “the movement of rock, debris or earth down a slope. They result from the failure of the materials, which make up the hill slope and are driven by the force of gravity. Landslides are known also as landslips, slumps or slope failure.” (Geoscience Australia, 2012). The purpose of this report is to evaluate four key factors that are primary to landslide research. This report will examine the causes and range of impacts of landslides on the population and the environment, the spatial distribution and temporal distribution of landslides. This report will look at The Thredbo landslide as a key example in the causes and impacts of landslides. After attempting to define key terms, the spatial and temporal distributions of landslides will then be addressed more generally (“Commentary on Guideline for Landslide Susceptibility, Hazard and Risk Zoning for Land Use Planning”, 2007, pp. 38-43).

What one event causes a landslide is difficult to determine as landslides are the result of many different contributing factors. They can range from a single boulder falling off the top of a slope to millions of tonnes of debris and earth moving down a slope, they can also vary in extent, with some occurring very locally and impacting a very small area or hill slope while others affect much larger regional areas. The distance travelled by landslide material can also differ significantly with slides travelling from a few centimeters to many kilometers depending on the volume of material, water content and gradient of the slope. In general the causes of landslides can be placed into two categories: natural and man-made. The most common natural causes are elevation of pore water pressure by saturation of slope material from either intense or prolonged rainfall and seepage, vibrations caused by earthquakes, undercutting of cliffs and banks by waves or river erosion, and volcanic eruptions. The man-man causes are the removal of vegetation, interference with or changes to natural drainage, leaking pipes such as water and sewer reticulation, modification of slopes by construction of roads, railways, buildings, the overloading of slopes, mining and quarrying activities, vibrations from heavy traffic, blasting, and the excavation or displacement of rocks. (Alex and Er, 1992, pp. 165--179) The scope of this report however cannot cover the extent of these causes and it would be recommended that further study be conducted in order to effectively analyse the causes of landslides in their entirety.

For the impact of landslides this report will focus primarily on the Thredbo Landslides that occurred in 1997. This is due to the Threbdo Landslides providing a real life scenario and example of the devastating nature of landslides which fulfills the aim of this report to provide the reader with an understanding of landslides through empathy, as opposed to facts and figures. The impacts of landslides are various and indiscriminate in their nature and have the potential to be extremely destructive.
On 30 June 1997 the Thredbo landslide occurred. As a result economic and social (population) impacts occurred. Evidently immediately after the landslide occurred, there were environmental impacts. Erosion played a huge role in damaging the natural environment of the affected area. When a part of a cliff or the origin of the landslide breaks off, it engulfs everything that goes in its path, which demonstrates as to why erosion was a significant environmental impact in the Thredbo landslide. Another environmental impact of the landslide was that there was a loss of topsoil. Hence, several floras were not able to grow due to the lack of soil and stability in the ground. Also, there was a great loss of vegetation and trees. Due to this, habitats of several different species of fauna were damaged and most were entirely demolished. The community expressed that they were regretful that they did not use vegetation on cliffs and hills to improve the stability of the area greatly prior to the landslide occurring. Before the disaster occurred, the street that was hit, Alpine Way was built with landfill, which seemed to be a mistake as it was not suitable for snowy conditions. The instability in the geographical and geological structure of Alpine Way allowed for the landslide to be arguably greater than it would have been in more stable conditions. As a result the destruction occurred on a large scale with much environmental damage and geographical wipe out. The effects of the landslide were long lasting with environmental regeneration being a timely process and restabilisation requiring much planning and investment.
The Thredbo landslide resulted in a very severe social impact on the community. At first, there was a fear that there was a second landslide to come. Several precautions were taken as a result as they began to build Alpine Way with a much more suitable filling (not landfill). In fear of a second landslide, tourists were timid and frightened to visit Thredbo. They also did not want to come to Thredbo due to the destruction of the town as the environment was severely impacted. Over time, the community of Thredbo was mourning for the losses of people who belonged to the community. This may have resulted however in grief and mourning, yet the community came as one and they helped the part of Thredbo that was affected rebuild and restore the morale of the ones who had lost loved ones and people close to them. (Landslides, 2007)
Staying relevant to Australia and the probability of landslides, this section of the report will focus on the spatial and temporal distribution of landslides. To predict the spatial and temporal patterns of areas susceptible to landslides, a distributed approach is needed that incorporates varying precipitation intensity, soil depth, vegetation (species, age, density), and root strength. In Australia, landslides are not a common occurrence. Landslides are more frequent and more likely to occur on higher ground. This is mainly due to the fact that the Australian landscape has an elevation that is relatively low, making it the lowest continent in the world. On average, Australia has an average elevation of 330 metres, which is low compared to Eurasia, which has an average elevation of 860 metres. Landslides usually occur on cliffs in coastal mountainsides, gorges, road cuttings or quarry faces. (Thredbo Alpine Village, 2011))

This is evident in the map recorded in 2007 by Geoscience in Australia (Fig.1). It is clear that the coastal cliff lines of New South Wales, Victoria and Queensland are highly populated with recorded landslide events. The Central zone of Australia is not prone to landslides to due its low elevation. This is contrasted to the coastal plains of New South Wales and Queensland, which has high elevation over 600 metres. These coastal areas are prone to landslides as they are adjacent to the Great Dividing Range. As seen in the map, Tasmania has had many landslides recorded. Tasmania has a substantial amount of Dolerite Mountains a type of igneous rock, prone to landslides that are located on highly elevated areas. Also, in Western Australia there are very few landslides recorded due to the low elevation and its location in relevance to the Nullabor Plain, which is a vast flat, arid area. (Landslides, 2007)

This report has identified key factors that play a role in landslides and has focused on the Thredbo Landslide. Using a key example from Australia and relating the report back to landslides occurring in Australia and made this report valid for Australian situations, as not every country experience landslides due to the same factors. The aim of analysing and identifying the 4 key themes of spatial and temporal distribution, and causes and impacts of landslides. Landslides. Overall landslides can have a devastating effect on social and environmental surroundings, and the spatial and temporal distribution of a landslide.