Just after midnight yesterday, Geologists Susan Humphris and Dan Fornari lowered the sixth dredge of this expedition over Knorr’s side near 24° 30’S latitude. From a map they made of the Central Indian Ridge rift valley (click here for a map of the ridge axis), they saw hints of a giant underwater mountain called a seamount. They concluded it was likely a volcano. (Click here to see the 3-D image of Knorr Seamount).

As their dredge descended through the blue-black of the Indian Ocean, they were eager to see what rocks they would collect from the seamount. Seamounts are not always volcanoes, but in this case, Susan and Dan’s volcanic suspicions were correct.

“This is super-fresh glass,” said Dan as he pulled shiny black basalt rocks from the dredge. The glass forms on the seafloor when hot lava spurting from deep with the Earth meets the icy ocean water. It was the proof that Susan and Dan needed that this large seamount was indeed an active volcano.

The Central Indian Ridge is part of the global mid-ocean ridge system, a nearly continuous 46,000 mile-long chain of mountains, mostly located on the seafloor. While it is not unusual to find a volcano on the mid-ocean ridge, they are generally not as big. The seamount has a long triangular shape, with a 24-mile length (40 km), an 11-mile width (18 km) and a height of 4,264 feet (1300 meters).

For an hour, Dan and Susan dragged the dredge, connected by a steel wire to a winch on the ship, across the seamount’s summit. At one point, the dredge “bit” or snagged on rock outcrops, causing violent tugs on the winch and tension up to nearly 10,000 pounds.

“Oops, there’s a good bite. There’s another bite, uh-oh· I think you’re hung up,” said Susan to Dan, who was controlling the winch. Eventually he cleared the snags and after an hour-long return transit, the shiny glass rocks landed on the deck with a thump.

Deeper Discovery

“We’ve got some great preliminary data and have an excellent bathymetric base map to start making a story of how this feature was created,” said Dan. “We’ve decided to name it “Knorr Seamount” in honor of this great ship and its crew.”

Scientists on board are excited by evidence of young volcanism on the seamount’s summit. Plume Team members Bob Collier, Marv Lilley, and Darryl Green all have a sparkle in their eyes knowing that they will do a CTD cast on the seamount’s summit later tonight to see if there are any indications of hydrothermal activity.

“Where there’s fire there’s smoke,” said Dan. “Fresh lava usually means you have a good heat source that can drive hydrothermal systems.”

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