A couple of Sitkans on a fishing trip in October got a surprise as they got ready to lay a skate of halibut gear in Nakwasina Sound.
Their depth sounder revealed a sizable steep-sided cone on the ocean bottom at a depth of about 200 feet, and it was emitting something into the water about 12 miles north of Sitka.
Jacyn Schmidt, regional geoscience specialist for the Central Council of Tlingit and Haida Indian Tribes of Alaska happened to be on the boat. Such phenomena are her field of interest, but she hadn’t expected to find an unmapped feature on the seafloor. “It was kind of a really funky coincidence.”
“Something uncharted is surprising,” she said. “It’d be interesting to know if it’s a new feature or if it’s something that has been there and maybe just was not noticed before.”
At the moment the boat passed over the feature, Schmidt was on deck handling the fishing gear and her friend was at the wheel in the cabin.
“We were just going to set a skate and then he called me into the cabin,” she recalled. Once inside, she saw the unexpected feature on the fish finder.
She immediately sent an image of the screen to Gary Greene, a retired marine geologist and scientist emeritus at Moss Landing Marine Laboratories in California.
Greene, who has years of experience studying seafloor phenomena, told the Sentinel in a phone interview that it’s probably a mud volcano.
“What it looks like is a mud volcano. ... I’ve been studying the mud volcanoes off of Dixon Entrance, which are associated with the Queen Charlotte Fault zone (near Haida Gwaii, in British Columbia),” he said.
They can be associated with true volcanism, “or they can be just associated with fluids coming up from deep in the substrate.” He’s reached out to the U.S. Geological Survey and hopes that core samples of the mound will be gathered and temperatures recorded.
“The best thing to do is run a multibeam sounder survey over the area in really high resolution to see what this thing looks like,” Greene said.
Game McGimsey, a scientist emeritus at the Alaska Volcano Observatory and U.S. Geological Survey, agreed that the cone on the seafloor is probably a mud volcano, but “it’s hard to be absolutely certain without more information,” he added. “It wouldn’t be uncommon for a mud volcano to be associated in that tectonic location.”
Recent volcanic and tectonic activity beneath Mt. Edgecumbe spurred an investigation by Alaska Volcano Observatory teams this past spring and summer. A swarm of small earthquakes in April led to the installation of monitoring equipment on the volcano that rises prominently on Sitka’s western horizon.
A mud volcano is quite different from a typical volcano that spews ash or lava, McGimsey noted.
“Mud volcanoes are just that — they don’t erupt magma. They basically consist of a sediment of some kind, water, and then a gas,” he said, “and the gas is what brings up the sediment to the surface. The gas can be a variety of things. In magmatic areas, carbon dioxide is the primary driving gas, and then in situations where mud volcanoes are also on land and associated with petroleum deposits, those mud volcanoes are usually driven by methane.”
Reader Comments(0)