Can a mountain turn into a river?

Can something be both a mountain and a river?

A dry, silent, still volcano moves,
and starts to burn itself from the core.
It burns until nothing is left but the fire itself.
Then it starts to overflow to its own mind, heart, body,
and keeps going to the rest of it.

Let it overflow and burn the whole world.

Leave nothing but yourself.

Take over me, make me what you are.

Drown me, make me lost in what you are.

You share what you have more of it.

You are fire from heaven.

You are fire holding oceans.

You are fire accepting tears like wood.

Heavier than water, lighter than stone I am.

I am what you are.

What am I?