A couple of loud explosions off the West Bengal coast triggered widespread panic in the beach tourists of Digha and Mandarmani at around 11am on Saturday morning. The explosions that seemed to take place out in the sea were so loud that window panes of a few hotels were shattered and there were reports of a few walls suffering cracks as well.
Midnapore district police officers told reporters that the sound was also heard from Tajpur, another popular tourist spot about 18km from Digha.
“We are looking into what actually happened. We have also informed the Coast Guard. The sound was also heard in Tajpur as well as in Digha,” Alok Rajoria, superintendent of police of the district.
After the explosion, the local administration forbade the tourists to go into the waters.
Incidentally, Indian missile testing range at Chandipur on Odisha coastline is about 50km from Digha. There were speculations whether missiles test fired from this spot accidentally landed close to the Bengal coastline.
However, defence sources said they had no confirmation of any wayward missile. They also pointed out test fired missiles don’t usually pack explosives.
There were also speculations that explosions could have carried out in the depths of the sea that might have caused the sonic boom that could have shattered the window panes.
Mysteriously loud noises have been reported for hundreds of years across the world. In Italian they are called “brontidi” (thunder-like); in Bangladesh they are “Barisal guns”. US citizens call them “skyquakes”, “moodus noises” and in North and South Carolina, “Seneca guns”.
There are many potential explanations, according to David Hill, a scientist at the US Geological Survey, who wrote a recent scientific review paper rounding up the causes of “mystery booms”.
In coastal regions, for instance, large bangs may accompany humungous waves hitting the cliffs; reports of thunderous sounds are apparently common among big-wave surfers in the US.
Some observers have also reported large rumbles accompanying tsunamis – sometimes alongside mysterious fire balls. For this reason, he proposes that both may come from a belch of methane erupting from “clathrate” crystals on the ocean floor. If that somehow ignites, it would create a massive blow.
Another possibility is meteors. Meteors can generate sonic booms and explode dramatically as they plummet from space. Given how long it can take a shockwave to reach the Earth's surface from the upper atmosphere, visible signs of the meteor can vanish before its sonic boom is heard, especially during the daytime, Hill noted.
Hill detailed this research in the 2015's September-October issue of the journal Seismological Research Letters.