Question

First of all, Hello all.

I have some question, I hope anyone can help me out.

The greatest source for heat in Middle Earth is ? (Can be a natural source or Magical). I suppose it is Mt. Doom, but I am not sure.

Why Elrond only wanted to destroy the ring in the Mt.Doom ? Is because the magic of the making of ring liked it there ? If so, there is any quote of Tolkien or even the characters to back up Elrond's idea ? I know the talk of Gandalf to Bilbo when he tell him to destroy the ring only there in the Fellowship of Ring book, but there Gandalf is vague of the reason to do there.
Thanks everyone