The Indonesian Navy submarine KRI Nanggala-402, which went missing last week (April 21) and was found on April 25 with all crew members deceased, was likely sunk by a powerful underwater wave known as an "internal wave", Indonesia's Navy stated via a report by Nikkei Asia.
Amid online speculation that the submarine may have sunk due to aging military equipment, the Indonesian Navy stated that a natural phenomenon known as an "internal solitary wave" was the likely cause of the sinking.
'No time to do anything'
Navy officers stated that differences in the density of waters off the coast of Bali and in the connected Lombok Strait are likely to have triggered a "massive movement" that resulted in the sinking of the submarine.
Commander of Indonesian Navy Staff and Command School Iwan Isnurwanto said "there was nothing that they could do no time to do anything... if the sub was brought down by such a wave. It likely angled [and veered downwards], causing all the crew members to roll down."
"We have to do further investigation, but that is most likely what happened," Isnurwanto continued.
Isnurwanto also stated that images from Japanese weather satellite Himawari 8 confirm that a strong internal wave was present in the submarine's location at the time of the accident.
What is an 'internal wave' exactly?
Unlike fast-moving, largely wind-powered surface waves, internal waves are enormous swells of water that can grow more than 2,000 (609 meters) feet in height and travel at speeds of three to six miles per hour (4.8-9.6 km/h) below the ocean's surface, according to a report by Seeker.
They are found throughout the world's oceans and usually occur when tidal forces cause two layers of different densities in the ocean's water to converge. The difference in density is typically manifested by different water temperatures, though it can also be due to a difference in salinity, the ESA explains.
The reaction between layers with internal waves is somewhat analogous to the reaction caused by friction between water and air for surface waves. However, internal waves carry immense momentum, typically unmatched by surface waves — internal waves can take a week to travel from New Zealand to Tasmania, for example.
The strong oceanic waves are thought to have caused scuba diver drownings — by pushing divers down hundreds of feet in minutes — and they also cause problems for oil rigs by exerting immense pressure on the offshore structures. A 2015 study by MIT researchers shed light on how internal waves are produced and concluded that the waves have wide-ranging effects on entire ecosystems and the global climate.
A brief timeline of the sinking of KRI Nanggala-402
The Indonesian Navy submarine KRI Nanggala-402 was first reported missing on April 21, when officials stated that they lost contact with the vessel during a torpedo drill in the Bali Strait, between the islands of Java and Bali.
A frantic rescue operation followed including help from the navies of Australia, Singapore, and the US. Hope for the rescue of the submarine's 53 crew members dwindled as Navy officials stated that the submarine would exhaust its oxygen supply by April 23.
During the search, aerial surveillance near the submarine's diving location found an oil spill, which was said at the time to be "highly likely" to have been caused by the KRI Nanggala-402 — giving a strong indication the vessel had sunk.
Sadly, on April 24, the Indonesian Navy released a statement saying the submarine had sunk, as debris from the vessel had been retrieved that would "have never got out of the submarine unless there was pressure." A recovery operation later found the sunken vessel, with all 53 crew members deceased.
Naval officials have since dismissed speculation linking the sinking of KRI Nanggala-402 to aging military equipment. They announced that more research is required into internal solitary waves in Indonesia's waters in order to avoid similar incidents occurring during future submarine missions.