Crater Lakes in the National Parks: From Crater Lake to Katmai's Acid Pools

Crater Lake National Park, Oregon. NPS photo.

Crater lakes fill the craters and calderas of volcanoes, usually with rain, snow and ice melt, and groundwater. Some hold fresh water; others are warm and strongly acidic from hot volcanic fluids. Lakes in calderas, the great hollows left when a volcano collapses, can be large and long-lived. Lakes in the craters of active composite volcanoes tend to be small, short-lived and as restless as the volcanoes themselves.

Caldera lakes

Because calderas are hollows formed by collapse, they can slowly fill to become lakes. Even so, they are not permanent: an outburst flood, a later eruption or the ground deforming can drain them.

Crater Lake, Oregon

The best-known volcanic lake in the national parks, Crater Lake is the deepest lake in the United States and the ninth deepest on Earth, at 1,949 feet (594 m). The eruption that formed its caldera happened 7,700 years ago, and the lake probably took about 460 years to fill, though estimates from rainfall range from 420 to 740 years.

An oblique view of the Crater Lake caldera, with the lake floor shown in shaded relief. USGS.

The same view, with features labelled. USGS.

Famous for its deep blue color, its clarity and its setting in the forests of the Cascades, the lake is 5 to 6 miles (8 to 10 km) across and lies entirely within the caldera, its surface about 1,000 feet (300 m) below the rim. It is a closed basin: no stream flows out. Most of its water comes from precipitation, with some from springs, and it loses water to evaporation and seepage, so its level varies with each year's rain and snow.

Mount Katmai, Alaska

By contrast, the lake in Mount Katmai's caldera in Katmai National Park and Preserve is young. The caldera formed in the 1912 eruption that created the Valley of Ten Thousand Smokes, and the lake is still rising.

Katmai caldera, looking northwest toward Mount Griggs and the Valley of Ten Thousand Smokes, with part of Trident Volcano at left. NPS photo by Chuck Lindsay.

• 1916–1917: National Geographic Society expeditions led by Robert Griggs climbed Katmai and saw a shallow lake.
• 1923: an expedition found the lake drained.
• 1951: the caldera held a lake about 524 feet (160 m) deep.
• 2010: the lake was about 787 feet (240 m) deep, still 689 feet (210 m) below the lowest point of the rim.

No one knows whether it will fill to the rim or settle at a steady level, as Crater Lake has.

Kaguyak Crater, Alaska

Kaguyak, also in Katmai, is a collapse caldera in a cluster of lava domes, formed in a large explosive eruption about 5,800 years ago where nine separate dome complexes once stood. Its lake is about 500 feet (150 m) deep, and its islands are domes pushed up after the collapse.

Kaguyak Crater and its lake. NPS photo by Chuck Lindsay.

Aniakchak, Alaska

A lake filled most of the 6.6-mile-wide (10.5 km) Aniakchak caldera soon after it formed 3,660 years ago. Wave-cut terraces on the caldera walls, and pillow basalts that only form in eruptions under water, record it. It stood at least 555 feet (169 m) above today's remnant lake and may have been nearly 1,000 feet (305 m) deep. About 1,800 years ago a great flood burst out through The Gates, draining most of it, scouring the Aniakchak River valley and leaving terraces and huge boulders downstream.

Aniakchak caldera from above. NPS.

The caldera with the outline of its former lake. NPS.

What remains, Surprise Lake, is about 64 feet (19.5 m) deep and fed by warm springs. It is the source of the Aniakchak River, which runs to the Pacific, and it gives sockeye salmon and Arctic char places to spawn and grow.

Lakes on active volcanoes

Craters on active volcanoes change with every eruption, and between them. In the national parks, the only composite volcanoes with active crater lakes are in Katmai:

Mount Douglas in front and Fourpeaked Mountain behind, September 30, 2006. USGS photo by Michael Poland.

• Mount Douglas has a small summit lake with steam vents. It is strongly acidic and warm, with a scum of sulfide minerals floating on it.
• Mount Mageik's youngest crater holds a lake 360 feet (110 m) across, very hot (198°F, 92°C) and very acidic. Vents beneath make it look as if it is boiling, and sulfide minerals turn it yellow-green.
• Mount Martin has a small lake and steam vents in its summit crater.

A brief lake on Kīlauea

Halemaʻumaʻu, the pit crater in Kīlauea's summit caldera in Hawaiʻi Volcanoes National Park, has often held a lake of lava. From July 2019 to December 2020 it held a short-lived lake of water instead, the first surface water there in at least 200 years, until a new eruption boiled it away.

Water in Kīlauea’s summit caldera, 2020. USGS photo by M. Patrick.

National park sites with crater lakes, present or past, include Aniakchak, Crater Lake, Hawaiʻi Volcanoes, Katmai, Valles Caldera and Yellowstone, where Yellowstone Lake lies partly within the Yellowstone Caldera.

Sources

• National Park Service, "Crater Lakes," Volcanic Features series; rewritten in hubnx's own words. Photographs and images: NPS and USGS.