A deep underwater trench, a 30-year-old military decision and a tsunami warning saved one of America’s most secret bases from any significant damage during last week’s tsunami, say U.S. officials.
Diego Garcia, a 10-square-mile British island leased to the U.S. Navy, sits in the middle of the Indian Ocean, just south of the hard-hit Maldives. From the tiny atoll, the United States monitors all manner of communications from around the Middle East, East Africa and southern Asia, whether Indian or Pakistani nuclear intentions or terrorist travels.
The island also has an airfield capable of handling nuclear bombers and a seaport where supplies for much of the region are stored aboard pre-positioned ships. Bombers launched from Diego Garcia flew missions over Iraq in Desert Storm in 1990-91 and in Operation Iraqi Freedom in 2003.
With an average height of 4 feet above sea level and a high point of only 22 feet, the island would have seemed to be as vulnerable as many other Indian Ocean islands to the tsunami that smashed into the coastline of Southeast Asia Christmas night and in the other direction sped across 3,000 miles of open water past Diego Garcia on the way to Africa.
Yet favorable ocean topography, including that deep underwater trench, and a fortunate decision by the Navy to place key facilities at the northern end of the island shielded Diego Garcia from major damage. While a 6-foot-high wave did hit the island, the underwater canyon essentially bore the brunt of the assault.
“There was no impact to facilities or personnel there,” one Navy official told NBC News, speaking on condition of anonymity. "There was minor debris and beach erosion at other areas of the island, but nothing significant.”
The Navy reports that more than anything else, “favorable ocean topography” minimized the tsunami's impact on the atoll. Diego Garcia is part of the Chagos Archipelago, which extends north from the Maldives. To the east lies the Chagos Trench, a 400-mile-long underwater canyon that ranges in depth from about 3,000 feet below the surface to 15,000 feet. It is one of the deepest regions in the Indian Ocean.
"The depth of the Chagos Trench and grade to the shores does not allow for tsunamis to build before passing the atoll. The result of the earthquake was seen as a tidal surge estimated at 6 feet," according to a Navy fact sheet.
John Pike of GlobalSecurity.org has noted that islands like Diego Garcia have natural defenses: "Small islands with steep slopes usually experience little run-up [from tsunamis] — wave heights there are only slightly greater than on the open ocean. This is the reason that islands with steep-sided fringing or barrier reefs are only at moderate risk from tsunamis.”
Moreover, the base at Diego Garcia received the Pacific Tsunami Warning Center's warnings, which are issued in Hawaii. The Navy official said the island gets the warnings routinely as part of the Navy's Pacific Fleet command structure even though it is located in the Indian Ocean.
A satellite image of Diego Garcia, taken on New Year’s Day south of India by Space Imaging, bears out the Navy's assessment.
“In this case commercial satellite imagery is useful to show areas that are still operational, especially since no reporters are allowed on Diego Garcia," said Mark Brender, Washington operations director for Space Imaging.
He noted that one image showed that KC-135 tankers, B-1 bombers and cocoon-shaped inflatable and portable B-2 stealth bomber hangars adjacent to a parking ramp were undamaged.
Bob Windrem is an NBC News investigative producer. Scott Foster is NBC's Pentagon producer. To see more satellite imagery, see the Digital Globe Web site.