Imminent Collapse

You have come upon a cave entrance in the northern Heathfells, on the border of Isengard, where you have encountered a rather unusual dwarf. Seemingly without heed to his own safety, he seems to have set about collapsing the cave entrance, which he claims leads to a warren of Orcs below.

Description
Stage 1
Stage 2

'Hey there, my good ${RACE}, I don't suppose you would be up for a quick bit of sport?

'This cave is packed full of Orcs, and I see no reason to leave it as is...it is better to seal the lot of them in the dark below!

'I have found a weak point in the rock here that should bring it down, but it will take a few minutes and make a whole lot of noise, so I could use a hand holding the Orcs off until I can bring it down.'

Help Ondor the Dwarf collapse the entrance to the Orc-cave.