Volume XXVII - 1996

A summary of results and observations from hydrothermal, biological, and geological submersible studies at Crater Lake National Park, 1988-1989.

I was sitting alone in Crater Lake, 600 feet underwater in a small submarine called Deep Rover. I had just completed collecting rock samples along an underwater edge of Wizard Island, and I had 135 pounds of rocks in a basket attached to the front of the submarine. Unknown to me at the time, a couple of O-ring seals were leaking throughout the dive. Water seeping through the seals into the submarine, combined with condensation from my breathing, created an uncomfortable amount of water on the floor. My feet were near the front of the vessel, and as I prepared to start to the surface with the rocks, the submarine tilted forward. As the submarine tipped, the water level at my feet rose rapidly, giving the distinct impression that the submarine was filling with water. Garbled and intermittent communications with the surface crew aggravated the situation. Everyone operated expertly and efficiently; Deep Rover and the rock samples were recovered smoothly. Actual dangers and repairs turned out to be minimal, and the submarine dove again the next day. Nonetheless, I thoroughly reviewed emergency procedures at my first opportunity.

Crater Lake partially fills the caldera of the Mount Mazama Volcano to an elevation of 6,172 feet. Once rising nearly a mile above the rim of the caldera, Mount Mazama experienced a climactic eruption and simultaneous collapse roughly 7,700 years ago. Crater Lake filled with water to nearly its present level within a few hundred years of the collapse. With a maximum depth of 1,932 feet, Crater Lake is the deepest lake in the United States. The lake is well known for its deep blue color and extreme water clarity, and visitors are amazed to see portions of the lake bottom at water depths up to 115 feet on calm days.

Enabling legislation for Crater Lake National Park and the National Park Service (NPS) allow for scientific study if there is no impairment of natural resources. As the fifth oldest national park in the United States, Crater Lake has a long tradition of hosting investigations aimed at obtaining information about the physical, chemical, and biological properties of the lake. Until 1982 lake research had to be done on a sporadic basis, as funding and personnel would allow. Congress then ordered the NPS to begin investigating Crater Lake in a more systematic way, and by 1986 directed that the park's hydrothermal resources be studied. A geothermal energy company was drilling exploratory wells adjacent to the park boundary, evaluating the potential for geothermal energy development, about the same time these requirements were passed. Although the objectives of the park's hydrothermal studies were not related to the drilling, undoubtedly this activity provided some political impetus to fund the research. As a result, the one- person submarine, Deep Rover, was flown into the caldera by helicopter to conduct hydrothermal studies in 1988 and 1989. Simultaneously, other studies, also using the submersible, were initiated to explore the distribution of deep-water plants and animals and to assess the early volcanic evolution and the postcaldera volcanic history of Mount Mazama.

Author in Deep Rover submersible, photo by Mathis Von Hesemans.

Operating a program that utilizes a submersible is a difficult undertaking in the best of settings, but especially challenging in remote areas at high altitude such as Crater Lake. The only access by land to the lake was the steep, one mile-long Cleetwood Cove Trail. Small four-wheel-drive tractors were the primary means of carrying supplies and materials from the top of the caldera to the lake shore on a daily basis. A base camp was established on Wizard Island and over 30,000 pounds of scientific and technical support equipment, including the 7,000-pound Deep Rover, were flown to the island by helicopter. The NPS insisted that no evidence of the operation remain on the island or in the lake after we were done. Researchers were meticulous in this regard and even transported dishwater out of the caldera.

Deep Rover is a highly technical submarine that the NPS, National Geographic Society, and U.S. Geological Survey leased from Can-Dive, Inc., a company based in Vancouver, British Columbia. The vessel is engineered for intuitive operation by its single occupant, who must serve as pilot and scientist. The operator sits in a five inch thick sphere of clear acrylic measuring six feet in diameter. This sphere is attached to two battery pods, each containing ten 12- volt marine batteries. The acrylic sphere opens at the bottom, like a clam shell, allowing the scientist to enter and exit. Mechanical, electrical, hydraulic, and life-support systems are mounted inside and outside of the sphere. Two large manipulator arms are mounted on the front of the submarine and are operated by the pilot inside. A basket mounted below the manipulators is used to stow scientific samples. Cameras, sample bottles, suction samplers, and sophisticated thermometers are other examples of equipment attached to the submarine. Learning how to operate Deep Rover required an intensive one-week training program that included classroom instruction and field work in operation, safety, and emergency response. This ensured that myself and two Oregon State University Oceanographers, Dr. Jack Dymond and Dr. Robert Collier, were ready by the time dives commenced in 1988.

Each dive day began with a trip to the dive site, which usually took one or two hours. Deep Rover was towed behind a research boat in a submersible "tender," designed specifically for use at Crater Lake. Once all systems were judged to be functional, the operator crawled through the narrow opening into Deep Rover, the submarine hull was sealed, and all outside noise was suddenly muted. Upon being sealed shut, Deep Rover heated up like a mini greenhouse, typically reaching 92° F before descending into the lake un-tethered. With permission to leave the surface, the pilot began the commute to the bottom of Crater Lake.

I had the distinct privilege of conducting 17 dives in Deep Rover. As I slowly sank into the depths of the lake, I was engulfed in blue which eventually turned to darkness. The only sounds in the submarine were the creaking and popping of the hull as it adjusted to the increasing water pressure and the persistent hum of the carbon dioxide scrubbers cleaning the air. The journey to the bottom could take up to 30 minutes, during which time my personal fears were easily extinguished by the intrigue and demands of the work. After reaching the bottom on my dive to the deepest part of Crater Lake, I shut off the scrubbers and instrument lights to better experience the solitude and quiet, and to briefly reflect on being the first person to visit the deepest part of the lake. After several moments, I looked up through the clear acrylic hull and noticed that the dive flag mounted on top of the submarine was visible, and silhouetted against a slightly lighter background. At 1,932 feet in depth my eyes could detect the vague light from the surface, a surprising testament to Crater Lake's incredible clarity. Yet there was little time for introspection. With less than six hours allowed per dive, I was fully occupied with monitoring electrical and life-support systems, operating the submarine, collecting samples, recording observations on tape and film, and communicating with the surface boat via an underwater wireless telephone. Although the submersible was designed to operate instinctively, many of the tasks I had to perform required extreme concentration and were mentally challenging, physically demanding, and sometimes frustrating.

Most of the lake floor is covered by fine sand colored sediments, and operating the sub there was like flying at night over an uncharted desert. One of the highlights of the research was discovery of bacteria colonies associated with hydrothermal fluids deep in the lake. These colonies form yellow-orange mats which appeared to hang on to or cascade down sediment slopes and rock outcrops. The mats consist of thousands of Gallionella and Leptothrix bacteria, which live on chemicals (primarily reduced iron) in the hydrothermal fluids that slowly enter Crater Lake through the lake sediments. It is unusual that the chemical energy from the fluids allows the colonies to live in darkness on the floor of the lake, independent of photosynthesis, since that process energizes most biological communities on the planet. Temperatures measured inside of the mats were as high as 68° F, whereas ambient water temperature was 38° F. Chemical geothermometry models suggest that source temperatures of 104 to 329° F would account for observed water chemistry and temperatures at the lake-sediment interface.

Another interesting discovery was the presence of discrete pools of saline water on the lake floor that had a distinct blue color. The first "blue pool" discovered was named Llao's Bath by Jack Dymond, after the legendary spirit of the lake. The pool resembled an oblong bath, 10 to 13 feet long and 3 to 5 feet across. It appeared to be elevated on one side by precipitates, and was surrounded by golden-colored bacteria. This pool and others like it are composed of hydrothermal water with salt content as much as ten times higher than the surrounding lake water. The presence of the salts makes the liquid in the pool heavier than lake water, and the pools appear blue because of the optical properties of the chemically enriched fluids. In general, many chemical indicators of hydrothermal origin were detected in fluids taken from the pools. In the most anomalous pool fluids, manganese was enriched by as much as a million times and Radon (²²²Rn) was enriched 100,000 times over typical lake values. Helium-3, perhaps the most distinctive indicator of a magmatic heat source, was enriched 500 times more than values for water in equilibrium with the atmosphere.

Llao's Bath and "brain" mat complex. Llao's Bath is in the foreground.
Drawing by Kathryn Brooksforce.

We were surprised to find another area of hydrothermal activity below the Palisades along the northeast caldera wall during one of the dives. Small stream-like features originated from underneath boulders or rock outcrops along the base of the caldera wall. The stream-like channels were two to three inches in width and equally as deep. Although no flow was observed at the time, the channels formed networks which exhibited classic erosional flow patterns. The channels were lined with brilliant gold bacteria and often terminated down slope in a series of blue pools. Twenty or more pools with associated islands, embayments, and delta-like features were observed in an area approximately 160 feet wide and 320 feet long.

Along the base of the east wall below Skell Head, remnant spires served as a record of past hydrothermal activity. Over 30 feet high, the spires had a chemistry indicative of a hydrothermal origin and a morphology consistent with underwater formation. Similar spires have been observed around active, high-temperature, hydrothermal sources in oceans around the world. The spires form when chemically rich hydrothermal fluids come in contact with cold ambient water and the chemicals precipitate out of solution to form chimneys around the vents.

In addition to the hydrothermal studies, Deep Rover provided a unique opportunity to survey the lake floor for plants and animals. Previous biological studies of Crater Lake were limited to sampling from a surface boat, collections along the shoreline, or shallow dives using SCUBA gear. During the submersible studies, several unusual and interesting biological discoveries were made. A thick band of moss, Drepanocladus aduncus, encircled the lake, and was observed growing at depths from 85 to 460 feet. It hung like icicles on vertical cliffs and formed thick lush fields on the gentler slopes around Wizard Island. The remarkable lower depth limit of 460 feet was due to the ability of light to penetrate deep into Crater Lake's clear water.

Animals were found living in Crater Lake's deepest basin at 1,932 feet below the surface. This was particularly fascinating because of the extreme water pressure that these animals must sustain to live at this depth. The deep-water animals were found at relatively low densities and included flatworms, nematodes, earthworms, copepods, ostracods, and the midge fly Heterotrissocladius. Many specimens survived the rapid pressure change during the retrieval from the lake floor and lived in the laboratory for several weeks after collection.

The geological studies conducted with Deep Rover expanded our knowledge of the eruptive history of Mount Mazama. Most of the rocks sampled from the caldera walls were lava flows which came from Mount Mazama, but a few samples collected from greater depth were rocks which predate Mount Mazama. These studies also provided new information on postcaldera volcanism by indicating which lava flows occurred beneath lake water and which erupted before the lake filled. Flows that formed the central platform, located east of Wizard Island, came about prior to the lake level reaching them. Merriam Cone and most of the submerged portion of Wizard Island formed beneath the water surface when the lake was approximately 250 feet below its present level. All of the postcaldera rocks sampled were andesite, with the exception of those from a small rhyodacite dome on the east flank of Wizard Island. The rhyodacite dome rises to approximately 100 feet of the lake surface and may have formed when the lake was close to its present level. The dome is the youngest volcanic feature known, with an age of approximately 5,000 years before present.

The dives were not without an element of mystery. I observed craters with a diameter of two to three inches in the deepest part of the lake. The origin of these craters is still unknown, though they may have formed from biological activity or from processes associated with gas and/or fluid release from the lake sediments. With so much to explore, it was hard to accept that the voltage remaining in the submarine's main batteries dictated the length of each dive. At the end of a typical six-hour dive, the temperature of the submarine was a comfortable 68 °F. Tired but still operating on adrenalin, I stretched the length of the dives out as long as possible. When the dive was over, air was added to the submarine's ballast tank allowing Deep Rover to slowly leave the lake floor. This was the first opportunity to relax during a dive. The ascent into natural light was peaceful. As Deep Rover rose and the water pressure decreased, air in the ballast tank would expand and spill out the base of the submarine rising around the sphere in a silvery blue veil of bubbles. Once on the surface, a crew of scientists and technicians quickly descended upon the submersible to secure and preserve the invaluable samples.

Deep Rover opened a brief and rare window of opportunity to view and explore secrets hidden at the depths of Crater Lake, yet less than two percent of the lake floor was explored. Discoveries from the submersible program not only provided valuable information on lake ecology and evolution important to understanding and protecting the lake. The program also documented previously unrecorded lush fields of moss, animals living at the bottom of the lake, and hydrothermal streams and vivid blue pools that supported exotic gardens of yellow-gold bacteria. The unusual scenes on the lake floor are consistent with the aerial view that visitors experience today; a sight only slightly altered from that which inspired people a century ago to dedicate themselves toward the establishment of Crater Lake National Park.

The author would like to thank cooperative biological investigators Gary L. Larson, C.D. McIntire, and Harry K Phinney, principal geological investigator Charles R. Bacon, and principal hydrothermal investigators Robert Collier and Jack Dymond. This program would not have been successful without the tireless work of submersible and scientific technical teams, and the staff of Crater Lake National Park.

Mark Buktenica has worked at Crater Lake since 1985 and is currently the park's aquatic ecologist.