August 30, 2012 19:37 PM
HONG KONG, Aug 30 (Bernama) — Hong Kong geologists have unveiled the whole picture of an ancient supervolcano in the territory while carrying out daily survey work, the first discovery of its kind in southeastern China.
The Hong Kong Civil Engineering and Development Department made an official announcement of the discovery here Thursday, Xinhua news agency reported.[mappress mapid="11"]
Located in the southeastern part of Hong Kong, the ancient supervolcano, known as High Island Supervolcano, was tilted on its side at about 30 degrees and has an original diametre of about 18 km.
It was thought to be the same type of modern-day collapse caldera that formed Taal crater in the Philippines, Tambora and Krakatau volcanoes in Indonesia, but on a much larger scale.
“The most important (thing) is that the source (of the volcano) was found,” Denise Tang, geotechnical engineer of the department, said at a press briefing held on a vessel near the Ninepin Islands where the whole system of the volcano could be seen.
When a volcano is defined as “super”, it erupts more than 1,000 cubic kilometres of ash, said Tang.
“There are about 50 supervolcanoes on record in the world,” she said.
Roderick Sewell, a veteran geologist of the department, said: “It didn’t happen overnight. The last piece of the puzzle was put, I’d say, in December 2008.”
Sewell told reporters that it took a lot of time and work to confirm the discovery, which was published in the U.S. geophysical journal Geochemistry, Geophysics, Geosystems in January 2012.
He said the discovery was an exciting one and hoped it would arouse the interest of Hong Kong people, especially children, in local geological features.
The High Island supervolcano last erupted 140 million years ago, and due to erosion and weathering, most of the volcanic rocks have been removed and only a remnant remains.
Spectacular large hexagonal rock columns, seen across a large area of eastern Sai Kung from High Island to Ninepin Islands within the Hong Kong Global Geopark of China which have been attracting loads of visitors, were in fact products of the eruption.
The department said the discovery has opened the way for further detailed analysis of the processes taking place in the large-scale eruptions and enabled better understanding of the origin of the rock columns that were formed.