Satellite images of the area where a nuclear submarine grounded two weeks ago clearly show a wedge-shaped undersea mountain that stretches across more than a kilometer of a desolate expanse of the South Pacific.
Defense officials have said the mountain, which rises within 30m of the surface, was not on the navigation charts that the Navy uses. One sailor was killed and 60 were injured when the submarine, the San Francisco, smashed into the mountain, or a reef jutting out from it, at high speed on Jan. 8.
The satellite images, taken in 1999 and early last year, suggest that the mountain is part of a larger range of undersea volcanoes and reefs. And they show that it sits more than 4.8km to the northwest of the nearest possible hazard on the charts.
Scientists who have studied the images say it is likely that the submarine's officers believed they had safely skirted the danger zone -- with the vessel about 165m below the surface -- only to crash head-on into the mountain.
David Sandwell, a geophysics professor at the Scripps Institution of Oceanography in San Diego, said it was also possible that the danger zone -- an oval area described as containing "discolored water" -- was a mistaken and poorly located reference to the undersea mountain.
US defense department officials have said that the notation dated to the early 1960s, and that it probably came from a surface ship that had spotted murky water. The discoloration could have been a temporary problem, like an oil slick, or a hazy indication of an undersea structure.
But the satellite images do not show any obstacles in that danger zone. And because it was hard for ships to get a precise fix on their coordinates before satellites came into wide use, Sandwell said, it is likely that the murky water was an early sign of the undersea mountain, and that the sailors who spotted it simply charted it in the wrong location.
"It seems relatively clear that that's what happened," he said.
Navy officials have said that the San Francisco, a nuclear attack submarine, crashed into the mountain 576km southeast of Guam on its way to Brisbane, Australia, a popular liberty port for sailors.
Its bow was severely damaged, and 23 sailors were hurt too badly to stand watch as the vessel limped back to Guam.
The exact location of the crash remains classified. But the undersea mountain shows up on the satellite images at a latitude of 7 degrees, 45.1 minutes north and a longitude of 147 degrees, 12.6 minutes east.
The Navy is looking into the crash, which occurred in a little used area that has never been systematically charted. Last week, the Navy reassigned the vessel's captain while investigators examine whether he bears any blame.
The main chart on the submarine was prepared by another agency within the defense department in 1989. Officials at the charting office have said they never had the resources to use the huge volumes of satellite data to improve their charts.
The submarine was traveling at more than 30 knots (55kph) -- close to its top speed -- when the accident occurred. Scientists said the images were taken by the government's Landsat 7 satellite.
Besides relying on charts, submarines also receive fixes from navigation satellites and take soundings of water depths. According to officials, the San Francisco's officers have said they took a sounding just four minutes before the crash, and it indicated that the vessel was still in 2,000m of water.