The mystery of the Seneca Drums persists

Below the surface, Seneca Lake's bed is a lunar landscape, with large pockmarks of unknown origin. Chloride levels are mysteriously high. And, most famously, occasional unexplained booming sounds - the Seneca Drums - emanate from the lake.

This summer, a team of scientists from Cornell, the State University of New York College of Environmental Science and Forestry and the New York State Department of Environmental Conservation set out to solve Seneca Lake's mysteries.

The largest and deepest of New York's Finger Lakes, Seneca Lake provides the drinking water for 100,000 people, including those who live in Geneva, Waterloo and Watkins Glen, New York.

In September the team took a DEC boat out onto the lake to sample water from its depths, inside the pockmarks and outside, looking for methane - which could explain the pockmarks and the sounds. They found methane, but the levels were the same inside the pockmarks as the rest of the lake, suggesting the pockmarks are not continually leaking gas.

"Now we're thinking these are episodic events where a bubble builds up in that sediment, and then it all erupts at one time," said Jed Sparks, professor and chair in the Department of Ecology and Evolutionary Biology in the College of Arts and Sciences. "Afterward, it's just the pockmark is left."

A small bubble at the bottom of the lake would grow about 40 times larger as it rises to the surface and water pressure decreases. The drum sounds may be big bubbles reaching the surface and popping, but it's unclear where the gas is coming from.

Sparks specializes in stable isotope analysis, which can differentiate methane produced by organisms in the sediment in the bottom of the lake and methane from fossil gas deposits below the lake bed.

Gas from fossil sources in the shales below the lake bed seemed most likely. "The bottom of the lake doesn't have any oxygen, so there are very few biogeochemical processes that make a gas," Sparks said.

However, his lab's analysis of the methane they found at the bottom was murky. The methane in the samples appears to be from a mix of biological and fossil sources.

"Typical science," Sparks said. "You think you're super smart and you know exactly what's going on, and you go measure something and realize you have no idea what's going on. But you're now able to ask the proper question to find out what's going on. It's usually a two- or three-step process."

The next step in the project may shed light on the chloride mystery.

Even factoring in chloride from human-made sources like road salt, Seneca Lake's chloride levels are higher than the other Finger Lakes and higher than is desirable for drinking water.

"There's always been this weird extra source of chloride that nobody knows about," Sparks said. "We're interested to see if there's chloride leaking out of these pockmarks as well."

To measure chloride at the bottom, the team placed long-term chloride and conductivity sensors on the lake bed in September. They'll retrieve the sensors in May.

"They're pretty cool," Sparks said. "They're sonically activated, so you send a sound signal when you want to get them back and they release, and then they float up from 600 feet."

Sparks hasn't given up on unlocking the secrets of the Seneca Drums, though.

He and Geoffrey Abers, the William and Katherine Snee Professor in Geological Sciences in Cornell Engineering, are exploring if they can place seismic listening gear in the south end of Seneca Lake and listen for the drums.

"We could get an idea of how often and how big they are," Sparks said, "and then you could start to put that into models."

While the Seneca Drums are among the most famous, the same phenomenon likely happens in other lakes.

"We don't just do science to make things that help us grow food faster," Sparks said. "We also do things just because it's really cool. I like living on this planet because it has these really interesting things in it."