The Mount Mazama volcano was one of the major Cascade Range volcanoes which formed during the Quaternary geochronological period. Before its caldera-forming eruption, Mount Mazama stood at an elevation between 10,800 to 12,100 feet which would place the summit about 1 mile (1.6 km) above the current lake surface and would have made Mount Mazama the highest peak in Oregon. However, following the last eruption, most all of the mountain collapsed into the caldera.

Mount Mazama formed as a group of overlapping volcanic edifices such as shield volcanoes and small composite cones, becoming active intermittently until its climactic eruption about 7,700 years ago. That eruption, the largest known within the Cascade Volcanic Arc in a million years, destroyed the entire summit of Mazama and reduced its height by about 1 mile. Further, that eruption is believed to have released about 12 cubic miles of magma to the surface, an eruption with a volcanic explosivity index of 6 on the scale of 0 to 8.

Much of the edifice fell into the partially emptied neck and magma chamber of the volcano and created the caldera. An ancient volcano, known today as Phantom Ship can still be seen rising above the lake surface from the eastern rim.

Mazama is dormant, but the US Geological Survey says eruptions on a smaller scale are likely, which could pose a threat to its surroundings.

After the eruption and collapse of Mount Mazama, a 12,000 foot high volcano about 7,700 years ago, Crater Lake began to fill the caldera that formed. Since that eruption, all volcanic activity within the park area has only occurred within the caldera.

There has been five post caldera vents which have extruded lava onto the caldera floor, including the vent forming Wizard Island, which has been the only eruption that has been able to break the surface of Crater Lake. These post caldera volcanoes, including Wizard Island volcano, were active while Crater Lake was filling with water.

The caldera, known as Crater Lake, is one of the best known in the world, and covers and area with a width of about 6 miles (10 km).

Crater Lake sits inside the volcano′s caldera and with a depth of 1,943 feet, it is the deepest body of freshwater in the United States and the second deepest in North America being second only to the Great Slave Lake in Canada.

Now, since there is no outlet or inlet flow of water, the water level of Crater Lake is maintained by a balance between precipitation, surface evaporation and seepage. Because this area of Oregon has an average annual rain water supply of about 88 inches, and the thick layer of permeable glacial till in the caldera wall serves as a drain, together, these two are the most significant factors effecting the lake level.

Crater Lake National Park covers an area of 250 square miles, including forest areas, alpine terrain, the Crater Lake, and the vast majority of Mount Mazama.

As a wilderness area, the national park was dedicated in 1902 and is overseen by the National Park Service. It receives about 500,000 visitors each year, and these tourists can go hiking, take bike, ranger-guided, and trolley tours, swim, fish, camp, and participate in other recreational activities.

The Park area remains open throughout the year, however, certain roads and facilities close in the winter season, particularly the northern parts of the park.

The Volcanic Legacy Scenic Byway, a road path journeys of over five hundred miles traverses the Crater Lake National Park.

Crater Lake National Park and the area surrounding Mount Mazama range in elevation from 4,000 to 8,929 feet, providing diverse habitats. In the Cascades, the topography and elevation have influenced local climate patterns, also shaping global climate when volcanic gas and dust have been released into the atmosphere.

The southern region of the park supports ponderosa pine forests, and for elevations from 5,000 to 7,000 feet, mixed coniferous, fir, and hemlock forests are common. Subalpine zones occur above 7,000 feet (2,100 m), often featuring whitebark pine.

From US 97, south of Chemult, Oregon, turn west on SH 138 and travel west about fifteen miles to a sign that reads Crater Lake: Left. Turn left onto the Crater Lake north entrance road and in a quarter mile arrive at the Crater Lake National Park sign. From here, it is another 15 miles, (which has numerous stops with overlooks of Crater Lake) to the Rim Village Drive where there is a cafe with gift shop, visitor center and the Crater Lake Lodge.

Native Americans have inhabited the area around Mazama and Crater Lake for several millennia and the volcano plays an important role in local folklore. The tribes that lived within the area were of those who were descendants of the Sons of Hadoram, particularly tribes of the Pacific interior plateau culture, especially the Klamath and Modoc indigenous people.

Lost Creek Campground (national park: 42.8795968, -122.0381230)

Mazama Campground (national park: 42.8673728, -122.1669941)

J. F. Kimball State Park, Oregon (primitive: 42.7331698, -121.9773262)

Caves and Karst

Cinder Cones Volcano

Geothermal Systems

Glacial formations

Hydrothermal features

Post Caldera Volcanoes

Pyroclastic flows and ignimbrites

Shield Volcano

Caldera Volcano

Volcanic Crater

Volcanic Vents

Crater Lake National Park

Pacific Crest National Scenic Trail

Crater Lake Lodge