USGS at Crater Lake for the past 100 years

By Gary Larson, Tania Larson, and Jennifer Rice

When Clarence Dutton of the USGS first visited Crater Lake, OR, in 1886, he was awestruck by its amazing beauty: "as the visitor reaches the brink of the cliff, he suddenly sees below him an expanse of ultramarine blue of a richness and intensity which he has probably never seen before, and will not be likely to see again."

With its mirror-like reflection and glassy smooth surface, the beauty of Crater Lake has enticed many people to visit this area.

This incredible blue lake is named for the enormous bowl-like depression in which it sits: the hollowed-out remains of Mount Mazama, a once mighty volcano whose catastrophic end was--until recently--a mystery.

In 1886, Dutton led the first USGS crew to study Crater Lake. They carried Cleetwood, a half-ton survey boat, up the steep slopes of Mount Mazama and lowered it onto the lake. Dutton spent nearly a month sounding its depths from the rowboat, using a lead weight and piano wire, and wondering at the forces that could create such a magnificent landscape.

In the more than 100 years since Dutton's historic first survey, a wide variety of scientists, using increasingly more sophisticated instruments, have come together and steadily unraveled the mystery of the demise of Mount Mazama and with it the formation of Crater Lake.

The colored region is shaded-relief bathymetry of the lake floor; the gray region is shaded-relief of the surrounding land. Merriam Cone is in the upper center of the lake. The distance across the lake is approximately 6 miles.

A world-class laboratory
Crater Lake is a place of spectacular beauty and a world-class research laboratory. The lake is nearly pristine, except for the consequences of fish introduction. Established as a national park in 1902, it has a high degree of protection from harmful human activities. Having such an extensive history of research and involvement with the lake provides many unique benefits for scientific study. Long-term monitoring is providing a baseline of information about its natural dynamics that serves as a reference for researching changes not only in Crater Lake but also in other lakes around the world.

Some of the most notable studies of the lake took place during 1988 and 1989. The USGS teamed up with the National Park Service and National Geographic Society to lease Deep Rover, a 7,000-pound one-man submarine flown in by helicopter to investigate the depths of the lake. Several dives were devoted to exploring the volcanic features on the lake floor and to sampling caldera-wall outcrops. The exploration with the submersible suggested the need for remapping the lake floor with modern techniques to provide a bathymetric (depth) map for interpreting the postcaldera geologic history and as a base for further study of the lake itself.

In 2000, scientists from the USGS, the National Park Service, the University of New Hampshire, and C & C Technologies used a high-resolution multibeam echo sounder to map the lake bottom. The new bathymetric survey provided a detailed view of the lake floor from its deepest basins virtually to the shoreline. Using Geographic Information Systems (GIS) applications, the bathymetry data can be visualized and analyzed, and has shed light on many Crater Lake mysteries.

What we have learned
Mount Mazama was a composite volcano that grew out of numerous smaller eruptions and other volcanoes over a period of 400,000 years. It had reached an approximate height of 12,000 feet before disaster struck.

It was over 7,700 years ago when a massive eruption, one that may have been the largest eruption in North America in the last several million years, spewed a towering column of pumice and ash some 30 miles into the air. The airfall from the eruption covered more than one million square miles of surface area, reaching as far as Southern Canada. As the tremendous amount of magma erupted out of the mountain, a monstrous cavern rapidly emptied beneath it and the summit collapsed. Between 10 and 13 cubic miles of mountaintop tumbled in on itself, filling the emptied magma chamber below and forming the caldera (the depression of a collapsed volcano).

Protruding from the sparkling yet calm surface is Wizard Island, named for its resemblance to a wizard's cone-shaped hat.

Decapitated though it was, the volcano was not yet ready to rest, and it wasn't long till activity pushed upward again. Today, the rugged and mostly barren cliffs of the caldera--and the dazzling waters that fill it--make a striking frame for Wizard Island, a small volcanic reminder that Mount Mazama may one day rise again. Sediments indicate that Wizard Island was formed shortly after the great eruption, while Merriam Cone, another postcaldera volcano hidden below the surface of the water, dates back to 5,100 years ago.

It took approximately 250 years for the crater to fill to its current water level. Sonar readings in 1959 recorded the deepest point at 1,932 feet, establishing Crater Lake as the deepest lake in the United States. The 2000 multibeam survey recorded the maximum depth at 1,949 feet. The lake maintains its current level because the amount of precipitation equals the evaporation and seepage rate. Moss grows in lush fields on shallow slopes and hangs like icicles on steeper grades in depths of up to 460 feet below the surface, a testament to the lake's superb water clarity, which averages 90 to 100 feet. Other biological wonders include the animals--earthworms, flatworms, nematodes, copepods, ostracods, and midge flies--found surviving the tremendous pressure at 1,932 feet, and the discovery of bacteria colonies associated with hydrothermal fluids on the lake bottom.

The lake floor is marked by the beautiful effects of hydrothermal activity: blue hydrothermal pools, deposit spires, and stream-like channels lined with the vibrant gold bacteria colonies. Pools of blue indicate the chemically enriched fluids where salinity concentrations up to ten times higher than surrounding lake water make the liquid heavier than the water around it. The small stream-like features show erosional flow patterns of these hydrothermal waters.

An ongoing study
Understanding the history and evolution of calderas like Crater Lake helps scientists predict when and where eruptions are likely to occur. USGS workers have used Crater Lake's well-preserved, detailed geologic history to develop a genetic model of small caldera evolution, and scientists from the USGS Cascades Volcano Observatory periodically make geodetic measurements and look for tilting or swelling of the caldera area that might forewarn of renewed volcanic activity. Though there may not have been volcanic activity at Crater Lake for a few thousand years, with a history spanning several hundred thousand years, it is likely that Mount Mazama will one day strive to return to its former glory.

Research at Crater Lake continues today as a collaborative effort of the USGS, National Park Service, Oregon State University, and others. As research continues, we learn more about the lake and monitor our success at managing it so that future generations can also marvel at this deep blue wonder.