If I recall correctly, the geography of Middle Earth was heavily changed during the wars between Morgoth and the Valas. I.e., it wasn't entirely shaped by natural processes but also by the willfull acts of semi-Gods
Meddlesome demons ruin everything. Too bad Feanor didn't think to create Stormbringer instead of the fucking Silmarils; he could have shoved it up Melkor's arse and then put the rest of the Valar and Maiar in their place.
