What crafted these crisscrossing lines in the Caspian Sea?

It’s a question that had Norman Kuring scratching his head earlier this month when he first saw this satellite image of the shallow waters surrounding the Tyuleniy Archipelago.

Mr. Kuring, an oceanographer for NASA, often examines images taken by the agency’s Landsat 8 satellite, which orbits some 440 miles above Earth. But he had never before seen what looks like underwater scars stretching for miles across the green and blue seafloor.

“I had no idea what they were,” he said. “I thought maybe they were marks of trawlers which sometimes disturb the bottom.”