An undersea collision that injured 11 crew members of a U.S. nuclear-powered submarine last month was caused by an uncharted seamount (an underwater mountain), the U.S. Navy says.

The USS Connecticut, a Seawolf-class fast attack submarine, hit the then-unidentified object in international waters in the South China Sea on Oct. 2, resulting in moderate to minor injuries. At the time, the Navy did not specify how much damage the vessel suffered. The sub was able to power its way to a port in Guam by traveling on the ocean's surface.

An investigation found that the Connecticut "grounded on an uncharted seamount," the 7th Fleet said in a statement.

It added that the fleet's commander will now weigh "whether follow-on actions — including accountability — are appropriate," implying that human error might have somehow played a role in the submarine's crisis.

A seamount near Guam was blamed for a submarine collision in 2005, when the USS San Francisco hit an uncharted seamount, resulting in numerous injuries and one death among the crew.

Researchers believe more than 100,000 seamounts rise more than 1,000 meters (about 3,300 feet) from the seafloor, according to the National Oceanic and Atmospheric Administration.

Most seamounts were formed by undersea volcanoes. They're common in oceanic basins, but only a small fraction of the world's seamounts have been explored. The habitats they create are seen as biological hot spots, hosting a wide range of marine life.

"New estimates suggest that, taken together, seamounts encompass about 28.8 million square kilometers of the Earth's surface," NOAA says. "That's larger than deserts, tundra, or any other single land-based global habitat on the planet."

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