Restore the Tears of the Mountain (3) | The Tears of the Mountain Darksiders 2 Guide

Start by picking up the rest of the items dropped by the boss and his Earth Crags. When you do it, use the newly unlocked passage. Your target is the switch shown on the above screen with which you need to interact.

[TIP: If you want to complete side quests connected with Karn, don't waste time trying to look for him, because he'll be waiting by the entrance to the dungeon involved in the next main quest.]