Why is Crater Lake, Oregon, not in the impact crater listing?
Crater Lake, Oregon was not formed by an impact event, even though it has the superficial appearance of some of the fresher (less eroded) impact structures. It was formed instead by the explosive eruption of Mount Mazama, a large andesitic volcano that stood at this location prior to the climactic eruption that destroyed it. The explosion blew the top off the mountain, similar to that which occurred in 1980 at Mount St Helens in neighbouring Washington State. Subsidence of the volcano, called caldera collapse, followed the eruption of Mount Mazama, forming the depression now filled with water, known as Crater Lake. Subsequent minor volcanism from a small fissure on the floor of the lake has constructed the small conical Wizard Island. This is not a central uplift.
