Grimrock

Some if not all of you probably already experienced tremors, but what does it mean?
Is it like in a rogue-type game where if you stay in a Level for too long something happens as a warning?
is there a limited time before grimrock explodes into a volcano or collapses?

When you First meet the Ranged Skeleton Soldier you'll see 2 pitfalls. I forget which floor it's probably the 2nd floor.

Can you please point to which part of the map the key is?