Mount Mazama is a composite volcano. It is made of multiple layers of lava flows and fragmented debris. Mount Mazama had a violent eruption around 5677 B.C., which caused the main height of the volcano to collapse and create a caldera, which holds Crater Lake.
Scientists consider Mount Mazama a unique volcano because it is made of multiple stratovolcanoes that overlap. These volcanoes were a mix of both composite and shield volcanoes. As they erupted or collapsed, they combined to create a taller, single volcano. After the massive eruption that collapsed the top of Mount Mazama, melting snow and rain filled the caldera for years, creating Crater Lake, which is the second-deepest lake in North America.