Because of Crabbe's poor navigation skills, instead of taking the easy route to Ithaca camp, he accidentally ends up taking his canoe down a waterfall. Before he goes down the waterfall, he experiences a lot of rapids.
After a very traumatic experience, Mary is a little out of it, some might even say suicidal. As her and Crabbe were walking quite high up, she falls and dies.
It starts to flurry and Crabbe thinks it's a good idea to go home instead of staying the winter alone in the wild. He underestimates the difficulty of traveling in the snow and wind, and ends up getting frostbite.