Aniakchak

Aniakchak National Monument protects 137,176 acres on the Alaska Peninsula, centered on one of the world's most dramatic volcanic features—the Aniakchak Caldera. This massive volcanic crater, six miles in diameter and 2,500 feet deep, formed approximately 3,500 years ago when a catastrophic eruption caused the summit of a volcanic cone to collapse. Within the caldera lies Surprise Lake, which drains through a dramatic breach in the caldera wall via the Aniakchak River, offering one of the most challenging and spectacular wilderness river trips in Alaska. The monument's extreme remoteness, severe weather, and challenging access make it one of the least-visited units in the National Park System, with fewer than 200 visitors most years.