Mountains and hills represent stability. They are the very foundation of creation, but even these are shaken and melt away in the face of the Lord’s judgment. There is no part of creation, no part of humanity that is untouched by his judgment.
In the New Testament, Peter speaks of the final judgment in a similar way (2 Peter 3:10–13). The heavens will pass away, and all things will be dissolved (melt away). But they will be replaced by a new heaven and a new earth.
5 The mountains quake before him; the hills melt; the earth heaves before him, the world and all who dwell in it.