America's deepest lake fills the crater left by a mountain that erupted itself apart

About 7,700 years ago, Mount Mazama in Oregon erupted so violently it emptied its own magma chamber and collapsed into a caldera nearly 2,000 feet deep. Rain and snowmelt slowly filled it with no river feeding in or out, producing Crater Lake — the deepest lake in the United States, famous for water so clear and blue that sunlight scatters through it almost like an open ocean. The Klamath people, who witnessed the eruption, still consider the lake, which they call Giiwas, sacred.

— Wikipedia contributors, Crater Lake National Park — Oregon, United States