Located in the southeastern part of Hong Kong, the ancient supervolcano is tilted on its side by about 30 degrees and had an original diameter of about 11 miles, the Hong Kong Civil Engineering and Development Department reported.
Geologists suspect it's the same type of modern-day collapse caldera that formed Taal crater in the Philippines, and Tambora and Krakatoa volcanoes in Indonesia, but on a much larger scale, China's official Xinhua News Agency reported.
A "supervolcano" is defined as one capable of emitting more than 240 cubic miles of ash, Denise Tang, geotechnical engineer with the department said, adding there were about 50 supervolcanoes on record in the world.
The Hong Kong example, known as the High Island Supervolcano, last erupted 140 million years ago, and erosion and weathering have removed most of the volcanic rocks until only a remnant remains, geologists said.
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