11 March 2022
Main Arm: a significant rainfall induced landslide in Australia
The eastern side of Australia has in recent days suffered a rainfall event of extreme severity, causing extensive floods and landslides, claiming at least 22 lives. It is hard to understand the magnitude of this event, and the degree to which it has varied from the long term record. The graph below, produced by the Guardian, shows the 2021-2022 cumulative rainfall to 8 March 2022 versus the long term trend for Brisbane. In this case, “very wet” is the 90th percentile:-
The event of the last week or so is extraordinary, taking cumulative rainfall to double the 90th percentile value for the time of year. This is a La Nina event, turbocharged by global heating, in action.
Unsurprisingly, this rainfall had triggered landslides. An area that has been severely affected in Main Arm in the Northern Rivers region in the northern part of New South Wales. The landslide below was triggered by the rainfall (image tweeted by Liam Mendes – @liammendes):-
@Liammendes has also tweeted another view of the landslide:-
This landslide appears to have occurred in deeply weathered residual soil or regolith. Note the house in the lower right side of the image, which has been destroyed by the landslide.
This is only one of a number of landslides in the area. Recovery from the disaster has been severely impacted by damage to the roads caused by landslides and washouts. Fortunately there have been no reported fatalities in Main Arm.