Jump over onto the walls, and use the hatchet to climb towards the edge.
Move along the upper edge of the wall and keep an eye on the Deathless' preparations for battle.
When Lara drops into the rift, try to go ahead and come out into the open.
A bit ahead, start climbing over the ice wall. Do not go left and go up, instead. Then, turn left.
Jump over onto the lips of the huge head, from the beam covered with ice. You will get near the newly-discovered camp. If you have any skill points that need distributing, you can do it now.
Past the camp, Lara will have to walk over a narrow ledge, while hugging the wall. At the same time, you can observe a team of the Deathless heading out to fight.