25 March 2021
Wongawallan: a damaging landslide in Australia
The eastern side of Australia has suffered devastating rains over the last few days, causing extensive flooding. There have been a number of landslides too, of which the most spectacular may be the one at Wongawallan in the Gold Coast hinterland in Queensland. This landslide appears to have affected the grounds of a very beautiful house. The image below, from Reddit, shows the site before the landslide:-
The image below shows the aftermath of the landslide, again the image is from Reddit:
Clearly for the homeowner this is a disastrous landslide, causing enormous levels of damage. Looking at Google Earth, it appears that the property was constructed between 2004 and 2009. The mound upon which it is located appears to be made ground, initially without the terraces, which appear to have been under construction is an image in November 2013. I wonder why the slope was terraced at this later stage? The Google Earth images might provide a clue, but I do not wish to speculate. The location of the landslide is -27.880° 153.245°.
The image below shows the state of the terraced slope, and the adjacent slopes, in 2016:-
The obvious part of the failure is the section of terraced slope directly below the house, but the landslide appears to have extended all the way down to the gates, a distance of about 110 metres:-
There are two obvious possible failure mechanisms here. It could be that the terraced mound has failed, loading the lower part of the slope, inducing failure lower down. An alternative is that the ground beneath the mound has failed, with the instability retrogressing though the mound. A proper site investigation is needed to ascertain the cause.
The impacts are unfortunately likely to be extremely expensive, and to be very disruptive for the owners of a beautiful property.