Hong Kong geologists have revealed for the first time the full extent of an ancient supervolcano with a diameter of 18km sitting beneath the former British colony.
The giant ash monster is thought to be of the same collapse caldera type as the infamous Krakatau volcano which killed tens of thousands and literally rocked the world when it blasted open near the Indonesian islands of Java and Sumatra in 1883.
The discovery - one of only around 50 such volcanoes in the world - is a coup for the local rock boffins, who have been digging around the Geopark in Sai Kun in the east of the Special Administrative Region for several years.
A supervolcano is one which is capable of producing 1,000 cubic kilometers of ash in an eruption. To put that in perspective, the hugely destructive Krakatau, whose explosion was said to be heard as far away as Perth, ejected only around 20 cubic kms.
The High Island supervolcano, as it has been dubbed, last erupted at least 140m years ago in the Mesozoic era, according to a report in local rag The Standard.
“This discovery was the result of years of very detailed, meticulous surveying work and very careful dating of the rocks," survey boss Roderick Sewell told the paper.
"It took a very long time to piece everything together into a story. It's a long road to discovery but when you suddenly get the 'aha! moment', it makes it all worthwhile."
Unfortunately the volcano has mostly eroded now so that little is still visible, although it apparently extends down as far as Kowloon and Hong Kong Island.
Local volcanophiles, however, can still see remnants of the monster ash-spewer in the form of large hexagonal columns of rock which dot the islands around Sai Kung. ®