The part of the hole where the guy on the right is standing looks to be about 10' deep, and those 'tiles' in the neighborhood of 2' thick by whatever their planar dimensions are.
By the looks of it, about a dozen of them were ripped up and tossed further down the spillway .. imagine one of those comin' at ya !
The right side of the hole appears to be about 30' deep, with lots of unconsolidated material in the egress area bottom right.