Crater Lake

How did a mountain become a lake? A massive volcanic eruption 7,700 years ago left a deep basin in the place where a mountain peak once stood. Centuries of rain and snow filled the basin, forming a deep blue lake whose waters are of unmatched color and clarity. It’s the deepest lake in the United States. Your trip to the rim to view the lake is climb up the flank of this trans-formed volcano.

JUST THE FACTS

How big is Crater Lake?

  • 6.02 miles across (maximum)
  • 4.54 miles across (minimum)
  • 1,943 feet deep at deepest point
  • Hold’s 4.9 trillion gallons of water
  • Tallest point on rim 1,978 feet above lake
  • Lowest point on rim 507 feet above lake

Did a meteor from the crater?

  • No. This deep basin is the belly of an erupted volcano
  • Its geologic name is a caldera

Why is the lake so blue?

  • Other colors of the spectrum are absorbed. Blue wavelengths are scattered and seen by human eyes

A Long Line of Cascade Range Volcanoes

Mount Mazama is one of a line of volcanoes ranging from northern California into British Columbia (diagram, far right). Along this zone, two of the earth’s crustal plates collide. As the denser plate of oceanic crust is forced deep into the earth’s interior beneath the continental plate, it encounters high temperatures and pressures that partially melt solid rock. About 7 million years ago the Cascades began to rise, where the molten rock surfaced as volcanic vents. This process continues. Lassen Peak and Mount St. Helens have erupted within the last century. Future eruptions may destroy the lake and fill the caldera with new rock.

GREW

1 for 400,000 years, repeated volcanic eruptions built 12,000-foot Mount Mazama. Thick lava oozed from vents on the mountain. Thinner lava burst to the surface in more spectacular displays of volcanic power. Glaciers formed and receded more than once.

BLEW

2 The most violent eruption began 7,700 years ago. A huge column of pumice and ash erupted skyward from a vent northeast of the summit, powered by expanding gas released from rising magma under great pressure in a chamber beneath the mountain.

FELL

3 New vents encircling the subsiding peak brought hot flows of pumice, ash, and gas down its flanks. As the magma chamber emptied, the mountain could not support its own weight and collapsed, forming a deep caldera where the snow-capped volcano once stood.

FILLED

4 The deep basin filled with centuries of train and snowfall. No streams run into the lake so very little sediment clouds its pure waters. Precipitation, balanced with evaporation and seepage, keeps the lake level consistent. Wizard Island erupted after the lake began to fill.

FUTURE?

5 It may now be asleep, but Mazama is not an extinct volcano. It may awaken with a new eruptive phase someday as the geologic processes that built the Cascade Range continue. Perhaps the violence of its past will return to once again transform this peaceful landscape.

Surprising Secrets of the Nation’s Deepest Lake

Research on the lake floor in Deep Rover, the submersible (left), found thick mats of bacteria thriving in the absence of light. Hydrothermal pools, unknown before, indicate the volcanic heat source beneath the lake. Thick bands of moss ring the walls at depths over 400 feet. Much remains to be learned; only two percent of the lake bottom has been explored.

A PRISTINE BENNCHMARK FOR CHANGE

Create lake’s purity makes it an indicator of human induced change studies here show possible impact of air pollution, climate change, and invasive species.

After his first visit here in 1885 William Glade stone steel (above) campaigned to protect Crater Lake, which he first heard about as a schoolboy. Steel’s work met success with the park’s creation in 1902.

The first attempt to determine lake depth, in 1886, was surprisingly accurate. Headed by Clarence Dutton of the U.S. Geological Survey, the Cleetwood Expedition was named for its boat (above).

A finding of 1,996 feet was taken that used a simple wooden sounding device to lower a section of pipe attached to piano wire.

Sonar equipment records the lake’s depth as 1,943 feet.

Park aquatic biologists (with moss, above) explored the lake floor in Deep Rover, in the research tradition that the Sonar equipment now records the lake’s depth as 1,943 feet.

Park aquatic biologists with moss, above) explored the lake floor in Deep Rover, in the research tradition that the Cleetwood Expedition launched. Moss beds discovered to encircle the lake and Wizard Island may weigh 50 times more than the rest of the lake’s living matter.

A science and Learning Center supports research and education efforts, connecting students, artists scientists, and the public to share the results of recent investigations. The scientists share their findings and contribute to the education work. An Artists-in-Residence program enables participants to offer the artists expression of their encounter with Crater Lake.

A midge fly (above) lays its eggs on the lake surface. The eggs sink nearly 2,000 feet to the lake bottom to hatch, feed as larvae, and mature as pupae. The pupa slowly wiggles and floats to the surface to emerge as an adult, and the cycle begin again.