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Coledale, NSW, 1988A booklet for Students and the Community
Chapter 10
THE NATURE OF LANDSLIDES
How They are Caused
Landslides usually involve the movement of large amounts of either earth, rock, sand or mud, or any combination of these.
Contributory Factors - Causes include earthquakes, volcanoes, soil saturation from rainfall or seepage, or human activity ( ie vegetation removal, construction of roads, railways or buildings on steep terrain).
Their Effects
Rate of Land Movement - This varies from exceptionally slow, only centimetres per year (which can damage roads, buildings, pipelines, etc) to a sudden total collapse or avalanche of perhaps millions of tonnes of debris, with the potential to crush vehicles, buildings and people, or to sweep away roads, power and telephone lines.
Degree of Land Movement - The distance travelled by landslide debris can also vary greatly, from a few centimetres in ‘ground slumps’, to many kilometres when large mud flows follow river valleys.
AUSTRALIAN LANDSLIDES
Since 1842, there have been hundreds of known landslides. Examples of areas affected by landslides in Australia are the Great Dividing Range (mainly on the steeper, moister coastal side), the Strzelecki and Otway Ranges of Victoria, the Mt Lofty Ranges near Adelaide SA, and the Tamar Valley and north-west coast of Tasmania. Our worst landslide was in the NSW Alps at Thredbo (see Case Study 4).
Serious Effects
Deaths and Injuries - It is worth noting that known deaths from landslides (at least 73) were about five times those caused by earthquakes (15) between 1842 and 1997, although the opposite applies to injuries (landslides=49, earthquakes=170). These deaths and injuries have resulted from 42 landslides and four earthquakes in Australia over that period.
Damage and Costs - In the same period more than 150 landslides have caused well over $200 million damage to buildings, roads, railways, pipelines and crops. A total of over 200 buildings are known to have sustained damage due to landslides. In the worst recorded case at Lawrence Vale, Launceston, Tasmania, 35 houses were destroyed in two adjacent landslides in the 1960s.
AUSTRALIAN REGION LANDSLIDES - CASE
STUDIES
1.
Coledale, NSW, 1988
On 30 April 1988 in this small coal mining town near Wollongong, a
landslide which resulted from a combination of human interference and two weeks of heavy
rainfall had fatal consequences. A 20 metre
high railway embankment collapsed after blocked drains caused earth and rock ballast in an
old mine dam to become saturated and cause severe undermining. A sudden rush of mud and rock collided with a
house below, turning it through a 60° angle before completely demolishing it and
tragically killing a woman and her infant son inside.
2. Finisterre Ra, PNG 1993
A powerful earthquake in the Morobe and Medang Provinces of Papua New Guinea set off massive, devastating landslides which: killed 37 people; destroyed two bridges, two airstrips and three villages; and damaged a further 58 villages as well as hundreds of food crops. Over 8,000 villagers had to be evacuated from the affected areas.
3. Gracetown, WA, 1996
On 27 September 1996, a 20 m high limestone sea-cliff collapsed on spectators at a school surf carnival at Cowaramup Bay near Gracetown (Margaret River). They had been sheltering from rain under the overhang when about 30 tonnes of rock and sand fell, killing nine people (4 adults and 5 children) and injuring three others. One survivor, a 10 year old girl, was dug from beneath the rubble by emergency workers after being trapped for 90 minutes, saved from suffocation by an air pocket. Miraculously, she survived with relatively minor injuries.
4. Thredbo, NSW, 1997
At about 11.30
pm on 30 July 1997 Australia’s worst landslide occurred when a large section of steep
mountainside below the Alpine Way road collapsed immediately above part of Thredbo Ski
Village in the NSW Alps. About 1,000 tonnes
of earth, rock and trees slid rapidly down the steep slope: firstly shearing the Carinya
Lodge off its foundations; and then,
causing it to collide with the Bimbadeen
Lodge at high speed. Both multi-level buildings were completely
crushed and their debris and parked cars scattered over and under the lower 250 m of the
400 m landslide. 
Rescue efforts were hampered by several further
minor ‘slides’ and the very
unstable mass of earth, rock, shattered lodges and trees and vehicles. All major emergency services took part in a
tedious and cautious search and rescue operation, firstly securing broken water, gas and
oil lines and precariously balanced boulders
and concrete slabs. Thermal imaging cameras
and seismic listening devices were used to aid in finding survivors. After 55 hours, rescuers located a survivor buried
in a void below three huge concrete slabs, 2.5 m below the rubble. Following 10 more hours of painstaking tunnelling
and shoring on the very steep, unstable slope, the slightly injured man was successfully
rescued. It was indeed a miracle he had
survived the complete demolition of his lodge, hypothermia from 65 hours with wet
clothing, and almost drowning after water entered his air space! He had endured three nights with air temperatures as low as
-12°C. Over seven days of exhaustive
searching, rescuers recovered the 18 bodies of those who died in this tragic disaster
which also caused damage worth many millions of dollars.
LANDSLIDE SURVIVAL
& PROPERTY PROTECTION
Local governments are heeding past lessons and now more thoroughly
investigate sites for instability before approving building developments. Land managers are also increasingly promoting
personal safety in dangerous and unstable areas. They
have erected safety fences and warning signs and even made physical changes to improve
some very unsafe features. Individuals can
help protect themselves in the following ways:
