IN THIS PICTURE YOU CAN SEE THE STRUCTURE OF CRATER LAKE. The structure is Caldera.

Crater Lake in Oregon, USA is the second deepest lake in North America and the ninth deepest on the planet. Crater Lake is famous for its deep blue color and  fore water clarity.

Volcanic activity in the area is fed by subduction off the coast of Oregon as the Juan de Fuca Plate slips below the North American Plate.

Last known eruption: 2850BC (?)

Most recent eruption 7,700 years ago.

Mazama is most famous for a catastrophic volcanic eruption that occurred around 5,677 (± 150) BC.[1][3] The eruption, estimated to have been 42 times more powerful than Mount St. Helens'

• Avarage hight from crater lake's surface to caldera rim. About 1,000 feet (305 m)
  
• The hight of the Mount Mazama volcano used to be 4,500 meters high
• Lake surface area 21 square miles( 54.4 km2)
• Lake is 11 kilometers across, and water is over 600 meters deep.