Thanks, glad you enjoyed it!
As for how it's done, it's a pretty straightforward brute forced solution. In essence, the map is a series of columns, with a full height and grass height. During the final frame of the full sized explosions, we do some circle math to figure out how much to remove from each column.
The map is generated by breaking the full playarea width apart into some random number of segments, setting key points for each segment and lerping between them. Little depressions of flat land are added after the map is generated for each of the tanks, by modifying the heightmap directly under them. And that's it!