Mountain climbing on Mount Rainier is difficult, involving traversing the largest glaciers in the U.S. south of Alaska. Most climbers require two to three days to reach the summit, with a success rate of approximately 50%, with weather and physical conditioning of the climbers being the most common reasons for failure. About 8,000 to 13,000 people attempt the climb each year, about 90% via routes from Camp Muir on the southeast flank, and most of the rest ascend Emmons Glacier via Camp Schurman on the northeast. Climbing teams require experience in glacier travel, self-rescue, and wilderness travel. All climbers who plan to climb above the high camps, Camp Muir and Camp Schurman, are required to purchase a Mount Rainier Climbing Pass and register for their climb.