Fires in Australia

To Sesa,
An arsonist is one that lights fires.
"The crime of maliciously, voluntarily, and willfully setting fire to the building, buildings, or other property of another or of burning one's own property for an improper purpose, as to collect insurance." - Arson
http://www.thefreedictionary.com/arsonist
Arsonist - one who commits Arson.
There are many motives for arson to be committed , such as insurance fraud, revenge, avenge.
Perhaps other sources of such fires include out-of-control campfires.
Hope that has helped you.