Adam Clarke on Psalms 83:14

The flame setteth the mountains on fire - This may refer to the burning of the straw and chaff, after the grain was threshed and winnowed. And as their threshing-floors were situated often on the hills or mountains, to take the advantage of the wind, the setting the mountains on fire may refer to the burning of the chaff, etc., in those places. Let them be like stubble driven away by the wind, and burnt by the fire.