Why is Crater Lake unique?

Answer 1

Crater Lake in Oregon is unique because it used to be a tall volcano called Mt. Mazama. It blew up about 7700 years ago leaving a caldera where a complex mountain peak once stood. Over the next 500 years or so it filled with water and became a lake. Since there are no natural inlets to the lake virtually all of the water in the lake is derived from snow falling directly into the caldera. The lack of external sources and turbidity make it one of, if not the most, clear and pure natural bodies of water on earth. At 1943 feet at it's deepest point it is the deepest lake in the United States and seventh deepest in the world. A sign of the most recent volcanic activity is Wizard Island, a cinder cone, which rises above the surface over 700 feet on the western edge of the lake.