She was a young, healthy person in what she believed was a manageable situation.

She had underestimated the distance and the conditions, but she was moving toward help, and she had not yet crossed the threshold into the territory where fear takes over from determination.

The cold was doing its work, though, whether she felt its full significance or not.

The human body responds to extreme cold in a programmatic way — a physiological cascade that begins as soon as the body detects that it is losing heat faster than it can generate it.

Blood vessels in the extremities constrict, redirecting blood flow toward the core to protect the vital organs.