Ancient ‘river bed’ on floor of Gulf of Alaska baffles experts. How did it get there?

The light sediment layer between the darker top and bottom layers tells a story of past geologic events on the ocean floor, says NOAA.
The light sediment layer between the darker top and bottom layers tells a story of past geologic events on the ocean floor, says NOAA.

The bottom of the Gulf of Alaska has never been dry land, experts say, so how can there be evidence of an ancient “river bed” etched in the mud nearly 1,000 feet down?

Stranger still, why did core samples taken last week at the site reveal sand that was “dry to the touch”? asks Sarah Hardy, an associate professor at the University of Alaska Fairbanks.

It’s a mystery perplexing scientists who explored the Gulf of Alaska for two weeks as part of a team backed by the National Oceanic and Atmospheric Administration.

“I saw what looks like a river bed on the seafloor... meandering just like rivers do on land, all the way to the edge of the Aleutian trench. But this area has never been above sea level, so how did it form?” Hardy asks in a report posted Saturday.

One idea: “A massive underwater mudslide,” she wrote, “but feel free to chime in if you know differently.”

It’s an area of seafloor, 985 feet down, that is considered “pretty quiet,” so experts expected core samples to be nothing more than “soft mud,” the report says.

But even that assumption was rattled, according to Hardy.

A NOAA team sent a remote vehicle to the ocean floor 39 miles off North Carolina to explore mysterious bubbling methane gas seeps.

“We found more evidence that this area has seen some action in the geological sense,” Hardy wrote. “Below the upper few centimeters of ‘normal’ seafloor mud, we found multiple layers of different colored sand, which actually felt dry to the touch.”

She likened it to pliable Kinetic Sand used by children — a squishy sand-like “toy” that is “completely dry” to the touch, according to the Kinetic Sand web site.

The oddities in the core sample added credence to her belief an ancient mudslide caused the “river bed,” Hardy says. Powerful seafloor currents caused by occasional mudslides “appear in the sedimentary record as layers of stuff that doesn’t look like it should be there,” she wrote.

“I’ve been a scientist for a pretty long time now, and one of the things I’ve learned over the years is that the more you learn, the more you realize how little you actually know,” Hardy says in the report.

The mission, which ended Aug. 3, was part of a project to “better understand the diversity of marine life in an under unexplored region of economic importance,” NOAA says in its mission overview.

The region is expected to “undergo unprecedented change” due to ongoing warming of the North Pacific, NOAA said.

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