Unbelievable.
I just had the same dream this night. I am not kidding!!!

It involved a huge volcano eruption, and just like you described, sending a massive piece of rock very high upwards, and an amazing ammount of lava flowing down that mountain. It looked huge. Reading your post shocked me.

But I live in Iceland and so I first thought this related to future and expected Katla eruption. No sense of date in my dream.