Crater Lake

Declared in 1902, it is the oldest national park in Oregon. Its lake formed some 7,700 years ago after the violent collapse of the Mount Mazama volcano, whose eruption — some 42 times more powerful than that of Mount St Helens in 1980 — left a caldera almost 10 km across which in time filled with rain and meltwater, with no river or stream feeding it and none draining it. At 594 metres deep it is the deepest lake in the United States and one of the deepest in the world, and its extraordinary purity — no sediment and no tributaries bringing in particles — gives it an intensely deep blue, celebrated among photographers and studied for its exceptional clarity.