Sting's head = 9.8 px = 0.25 m
Diameter of cylinder (minimum) = 935 px = 23.8 m
Panel height = 1047 px
Object = 2atan(Object_Size/Panel_Height/(tan(70/2))) = 0.37 degrees
Using this calculator the distance is 38.7 m
Destroyed volume is a cylinder
V = π *r^2 * h
V = 17216.89 m^3
Rock was violently fragmentized
Energy for violent frag = 120 J/cc
Energy = 2.06e12 Joules ( 493 Tons of TNT ) or Multi City Block level
But there are some things that aren't taken into consideration on the above calc that i think cancel each other, 1.There are tunnels below the arena so the the destroed should be the cylinder volume multiplied by 0.5 or 0.75
2.Natsu and Gajeel keept falling after the above picture so the height of the cylinder is a bit bigger
3.The diameter i scaled on the panel is a part of the entire diameter of the crater.