USA — Can a landslide spontaneously combust? It can if it contains the right kind of rocks.
In August 2004, fire crews attended a wildfire near Santa Barbara, California. After hosing down the burning grass, they traced the fire to a recent landslide, but had no idea how it started.
A few weeks later, Robert Mariner, from the US Geological Survey in Menlo Park, California, and his colleagues visited the site and found that the temperature of the rocks in the landslide was 307 ° C – hot enough to start a fire. The analysis of gas from boreholes ruled out geological ignition sources such as volcanic activity or flammable natural gas, so it appeared that a chemical reaction in the rocks caused the ignition.
The landslide exposed a mineral called pyrite to the air, causing an oxidation reaction that heated a nearby patch of low-grade coal to more than 300 ° C (Geology,DOI: 10.1130/G25285A.1).
Ian West at the University of Southampton, UK, thinks that landslide fires may be more common than we realise: “There have been a few along the UK’s Dorset coast in the last few hundred years, and there are records of a huge fire in the Dead Sea area, dating from King Solomon’s time, which may have started this way.”