Seneca Lake, in New York State’s Finger Lakes region, was formed tens of thousands of years ago by the retreat of the glaciers that once covered much of northern North America. The lake is incredibly deep. It’s about 1,200 feet down to the bedrock (that’s below sea level!), but it has been filled in by about 600 feet of sediment since the glaciers retreated about 11,700 years ago. During the last six years, extraordinary discoveries have been made about the lake’s origins and dynamics, as well as its historic cultural value.

These discoveries are the results of a detailed archeological and bathymetric (underwater terrain) study conducted by a group of scientists, supported by the New York State Department of Environmental Conservation (DEC); the State Office of Parks, Recreation, and Historic Preservation; and the New York State Canal Corporation. Dozens of Canal-era shipwrecks have been found, including a first-of-its kind original Erie Canal packet boat, which is being hailed as the “holy grail” by canal historians. In addition, scientists discovered a topographic ridge-like structure along the bottom of Seneca Lake that had never been previously observed or mapped.

“The joy of discovery is an exciting thing,” said Art Cohn, principal investigator for the Seneca Lake bathymetry project and shipwreck historian. “It’s so exciting.”

Cohn, and his partner on the project, Tom Manley, a Middlebury College oceanographer, lead the adventure with assistance from Lewis McCaffrey, a DEC PhD geologist and hydrogeologist. Cohn and Manley credit DEC and other State agencies for “tremendous support” that led directly to groundbreaking scientific and cultural discoveries made in Seneca Lake. DEC supported the survey with funding from the New York State Environmental Protection Fund, which covered the rental of the research vessel, R/V Folger, and specialized sonar gear used in the survey.

Why Seneca Lake? Seneca Lake’s amazing discoveries occurred, in a way, by accident.   Cohn and Manley are renowned for their decades-long work surveying the bottom of Lake Champlain. In 2018, Cohn was asked by the New York State Canal Corporation to assist the Corning Museum of Glass in recreating a journey through New York State’s inland waterways to highlight the 150th anniversary of the Brooklyn Glass Works’ move to Corning.

“In its day,” Cohn explained, “Seneca Lake was a transportation superhighway of maritime commerce. And the more activity there is on a body of water, the more potential there is for submerged cultural remains.” What was found through the bathymetric study was overwhelming. The number and diversity of the discoveries, as well as the historical and scientific informational value, is incalculable. “People are going to find it a game-changer,” Manley said.

Technology to Discover Think of the United States Navy-developed multi-beam sonar technology used to canvas Seneca Lake as a fish finder. Actually, more like 512 fish finders packed into a single unit and specially synchronized to collect data simultaneously from 512 different points on the lake’s bottom. The precisely engineered sensors are contained within a nearly 18-inch-wide pod that’s about six inches thick and mounted on the sides of the research vessel. There are 256 sensors that are focused on the starboard side and another 256 sensors focused on the port side. The data collected at any given time varies depending on several factors, including the depth of the lake and the speed of the vessel.

“We’re technically swath-mapping the bottom of the lake,” Manley explained. “It’s created like you’re mowing the lawn. It’s like creating a mosaic of everything that’s on the bottom.”   The dataset generated replaces archaic National Oceanic and Atmospheric Administration’s depth charts, which were created a century ago using lead weights, a long, marked rope, and positional estimates by triangulation. The new sonar is up to 20,000 times more precise and it maps the lake in ultra-high detail. “Any large object that is down there is going to pop out very, very strongly,” Manley said.

Discoveries Most who are familiar with Seneca Lake know about the “Belhurst Castle Hole”–an area near the famed Belhurst Castle in Geneva where, on the north side of the 38-mile-long lake, a localized spot at the lake bottom is much deeper than the surrounding lakebed. The survey showed that the hole may not just be a single structure, but instead a bathymetric complex of which the Belhurst Castle Hole is only one part. It’s a ground-breaking discovery.   Stunning detail from the bathymetry survey revealed that beyond the Belhurst Castle hole, there also appear to be five additional holes in the area—potentially making this area of the lakebed part of a much larger complex. Scientists think the complex of holes were generated by crumbling of the underlying salt structures, which are common in the crust of the Finger Lakes, which may be dissolving and slowly sculpting the complex.

“This is the kind of detail we’re seeing with the multi-beam data,” Manley said. “There is a lot of information that this higher resolution data is now providing that basically shows us what we really don’t know about Seneca Lake.” Another ground-breaking discovery that has generated many more questions than answers, is the 144 depressions or pockmarks that were found on the southern end of Seneca Lake. “They’re big holes, and we don’t know what caused them,” DEC’s McCaffrey said. However, there is a growing consensus that it is upward migrating methane gas from the Marcellus formation. “These large pockmarks are most likely gas or methane-derived, but we don’t know how old or active they are.”

The pockmarks range in size from the footprint of a house to nearly three American football fields and are up to 60 feet deep. The largest pockmark is about 300 meters (just under 1,000 feet) in diameter and ranks up there among the largest pockmarks observed in the oceans. The largest single inventory of pockmarks in the world were first discovered decades ago using multi-beam sonar in Penobscot Bay, off the coast of Maine. Hundreds of the isolated depressions are known to exist there and are linked to methane escaping from the seabed.

“These pockmarks are a world-wide phenomenon. They exist in the oceans and lakes,” Manley said. In Seneca Lake, McCaffrey speculates it could be some type of fluid that’s emanating up from the bedrock through the more than 600 feet of lake bottom sediment. It could be natural methane gas, given that the Marcellus Shale Formation lies directly below the lake in this area, or it could be from water.

“These are the geological and environmental questions that are just opening up,” Manley said. “Why do they appear here? Why not in the northern part of the lake? Why don’t they exist on land?”   As if those geological discoveries weren’t enough, there’s another interesting feature: The topographic ridge-like structure along the center of the bottom of Seneca Lake. The science isn’t settled on what the structure is. It could be a ridge, or it could be a glacially created esker, which is a long, somewhat linear mound of sediment created by a retreating glacier.   “We don’t know,” Manley said. “We just don’t have the information.”

Shipwrecks The historical insights about past societies that will flow from the study of the archaeological discoveries identified during the Seneca Lake Bathymetric study are as profound as the geophysical discoveries. The R/V Folger and its crew have already documented and confirmed some 50 new shipwrecks in Seneca Lake. More remarkably, the team’s archaeologists believe that as many as 50 additional cultural targets will prove to be intact wooden shipwrecks, many of which will likely date back to the infancy of the Erie Canal.  “The minute we got to Seneca Lake and put a sonar in the water, we began finding shipwrecks, lots of shipwrecks,” Cohn said. “Most of them were completely intact with cargos, including a first-generation Erie Canal packet boat.”

Added Cohn: "Erie Canal packet boats are well known in history through newspaper ads, travelers’ journals, and artwork, but no archaeological example had yet been found. A replica of the 1825 packet boat Seneca Chief is currently being built in Buffalo by the Buffalo Maritime Center. Finding an archaeological original would be a major maritime discovery." 

 

Cohn, a nautical archeologist who has dedicated decades of his to life finding and documenting shipwrecks and advocating for their preservation, explained, “Because Seneca Lake is a deep lake, filled with cold, freshwater, it preserves its shipwrecks well. We never would have expected to locate this many intact, Canal-era shipwrecks that communicate as a collection so much information about the early canal.” The cultural value to maritime history is immeasurable.