Given its remote location and challenging weather conditions, Aniakchak is one of the most wild and least visited places in the National Park System. This landscape is a vibrant reminder of Alaska's location in the volcanically active "Ring of Fire," as it is home to an impressive six mile (10 km) wide, 2,500 ft (762 m) deep caldera formed during a massive volcanic eruption 3,500 years ago.

...Excerpt from NPS website