3. Rocks and Weathering Case Study Flashcards
What is the case study
The Abbortsford landslide, Dunedin
When did it happen
8th August 1979
What were the early signs that something was going to happen?
Cracks in their houses,
water main pulled apart
The water had made layers of clay on the hill soft, and the sandstone above it was sliding
How did the authorities react
Civil defence emergency was declared on 6th August
What was the damage
69 homes were destroyed and 600 people were displaced
What was the total cost for the destruction
7 million pounds
What were the effects of the landslide on people?
depressed house prices
Psychological trauma
public inquiry
What made up the landslide
A block slide of sandstone resting on a weaker bed of clay. Permeable hard rock resting on an impermeable soft rock.
What was the angle of the slope
7 degrees
What processes caused the landslide
Water was absorbed into the porous clay which reduced its strength and cohesion. this caused the sandstone to slip along the boundary of the 2
How much did material did the sandstone involve
5.4 million meters cubed
How long did the landslide last
30 minutes, at a speed of 1.7m per minute
What other factors contributed to the landslide
Deforestation
Reduced evapotranspiration
less binding of the soil with plant roots
Urbanisation cutting and infilling
Surface drainage increased the removal of water
Quarrying at the base removed support
What triggered the landslide
Leaking water pipes, heavy rainfall
What can be learnt about the abbortsford landslide
Landslides can occur on gentle slopes
Attention to early warning signs can save lives
Human activity can destabilise slopes
