If you can get this video to play and loop, it is quite interesting.
Lighting strikes the tops of the trees in the picture.
Notice how the ground shoots upward at the base of the trees and bushes. You also see splinters of trees fall to the ground.
I am only speculating, but since it's usually the heat that causes the trees to "splinter" when hit by lightning, that may be what causes the ground to explode upward.