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Diving into mysterious Crater Lake

Scientists use aquatic robots and highly sensitive sonar to study its pristine, self-contained ecology. Photos: A water-filled crater Video: Deep-diving robot

CRATER LAKE, Ore.--One of the tourist signs at an overlook here is as striking as the scenery: "You are standing in a volcano."

Yet the implicit danger of the sign seems to get washed away by the pristine, vivid-blue lake below, which from the vantage point of the rim 1,000 feet up, looks like a massive, rock-lined bathtub.

Researchers here are going deep into the giant volcanic hole with aquatic robots and highly sensitive sonar. The lake, formed by a massive eruption 7,700 years ago, is one of the world's purest bodies of fresh water and, at 1,932 feet, one of its deepest. Most interesting to scientists, it's had little mixing with the outside world--no feeder creeks, no rivers, just snowmelt and rainwater.

Crater Lake

"This is a simple system we're just beginning to understand," said Irja Galvan, a professor of biology at Oregon State University, who was here Tuesday visiting friends who are studying Crater Lake.

Scientists from Oregon State and the U.S. Geological Survey were conducting field studies this week on the lake's ecology. The project included lifting a submersible robot down onto the lake by helicopter and sending it deep into the water to collect digital video, data and moss samples. The scientists plan to compare the samples and data to research from the late 1980s, when the scientists first described moss beds at the bottom.

Part of the researchers' goal here is to assess how much moss is contained in the lake, how old it is and then add up all the carbon to understand the ecosystem of the lake. Because there are so few nutrients in the lake as a whole, the moss colonies are rare homes to life such as tiny worms and crustaceans, which are fish food to only two breeds of fish that live in the lake--kokanee salmon and rainbow trout. As many as 40 other kinds of fish introduced to the lake over hundreds of years have died off.

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Video: Robot dives to lake's bottom
Latest rover explores the depths of one of the clearest bodies of water in the world.

What aquatic scientists can say for sure is that despite a near lack of nutrients in the water--which plants and other aquatic life need to survive--the lake is home to colonies of moss, as well as bacteria at the lake floor. It also hosts a small population of sturdy fish, introduced to the lake by humans in the late 1800s. There are also hydrothermal vents that heat up pockets of the bottom of the lake to 68 degrees (when all other water at the bottom is 38 degrees) and prove the volcano is still active after a half a million years.

By studying this little-understood, closed ecosystem, the scientists hope to gain greater understanding of the lake's history and functions on the whole. In the process, they also plan to set benchmarks for the water's vital signs that could help trace environmental and ecological change happening today and in the future.

"Moss is a big part of this ecosystem, one which we know little about," said Robert Collier, associate professor of chemical oceanography at Oregon State, who was giving scientific talks Tuesday at Crater Lake's Sinnott Memorial Overlook.

The research could also have an impact on research into pollution and ultraviolet radiation. "This is the clearest body of water to (ultraviolet) light that we've ever studied, and in the world, because of low concentration of particles and nutrients available for algae and aquatic plant growth," Collier said.

Crater Lake is ancient. The freshwater lake began to form nearly 7,700 years ago when the volcano, Mount Mazama, at a former elevation of 12,000 feet, violently erupted and collapsed on itself with enough force to incinerate parts of Oregon and spewing ash as far as Vancouver and Kansas. The event exerted 46 times more force than that of San Francisco's 1906 earthquake.

Scientists believe that after the volcanic hole left in Oregon's Cascade Range cooled off, it filled up with snowmelt and rainwater during the next 600 to 800 years to form Crater Lake. Because the volcanic terrain limits the amount of nutrients in the lake, and prevents streams coming in or out of it, the water is pure blue and largely comprised of snowmelt.

The volcano erupted again nearly 4,000 years ago to form volcanic structures within the lake--the largest of which is Wizard Island.

Wizard Island is the focus of much of today's field studies, because the scientists have found thick concentrations of moss hanging like icicles from the island's steep edges. The team is also trying to understand the many large pits within the old moss beds, which when examined show layers of green and white algae, with live cells growing at the tips of the moss.

"At this point, it's all a mystery," Collier said.

In 1988 and 1989, a team of researchers sent the first human-driven submarines into the lake. Now, the team of scientists is using one of the most powerful remotely controlled robots, as well as high-resolution sonar beams to collect data and construct a map of the ecosystem under the lake's surface.

"With the crazy depths of this stuff, this kind of technology is the only way we can get to it," said Mark Buktenica, an aquatic scientist and lead researcher. Buktenica was referring to the limits of scuba diving in the lake--divers can typically only go as far as 100 feet deep before getting sick due to the altitude.

On Tuesday, the scientists were exploring an area of the lake called Danger Bay with a remotely operated vehicle, or ROV robot, which is capable of diving 1,500 feet. (The ROVs are typically used as rescue vehicles.) The moss beds start at depths of 85 feet and go down as far as 600 feet.

The ROV robot is equipped with two high-definition digital cameras, one that takes color video and another for black and white, as well as GPS for navigation. Sonar on the top of the robot also collects data on the biomass of the moss, blue-green algae, and other life in the lake.

It has seven thrusters--four mechanisms to go forward and reverse, two to go side to side, and one to spin. The device is also neutrally buoyant, meaning that it doesn't sink or float. It's controlled by an altimeter, which measures depth and can be set to stay a certain distance from the lake floor or wall.

Two engineers on a boat control the robot's movements. And data and video from the robot is transmitted via wire to a computer on the deck of the boat. The PC takes in and transmits signals from the altimeter.

Early assumptions about the moss are that it is nearly 6,000 years old, or as old as the lake itself. But dating the moss is tricky, given that carbon-dating techniques don't work on the almost nutrient-free environment of the lake. Instead, the scientists are attempting to date the pollen that blows into the lake and gets embedded in the sediment.

On Tuesday, the views of Crater Lake were slightly veiled by ash and smoke from a wildfire in the forests around the lake. Brian Kahn, a park ranger with the National Park Service, said that the fire started July 23 after a dramatic storm sent temperatures from 90 degrees to 60 degrees within an hour, and lightning torched parts of the forest. The storm was so fierce that tourists were trapped on Wizard Island.

But a nearby fire isn't going to dampen the enthusiasm of the lake researchers about the local environment.

"We're talking about hundreds of thousands of years of geology exposed," Collier said.