Scientists discover that downtown Hong Kong sits above remnants from an extinct super volcano that last erupted 140 million years ago.

Downtown Hong Kong sits above remnants from an extinct super volcano, the first of its kind to be discovered in south-east China, announced Hong Kong government scientists on Thursday (August 30).

A "super volcano" is a volcano that erupts more than 240 cubic miles.

The newly-discovered High Island Super volcano in Hong Kong spurted out 1,300 cubic kilometers of ash about 140 million years ago, near the end of the Jurassic period.

The super volcanic eruption on the southeastern China seaboard would have produced a global environmental impact and could be related to the extinction of dinosaurs, according to handout from Hong Kong's Geotechnical Engineering Office that conducted the research.

While millions of years of erosion removed a large part of the super volcano, it left its most visible footprints in the tall, leaning hexagonal columns in eastern Hong Kong's Ninepin Island chain.

After the eruption, cooled volcanic ash became rocks, which slowly contracted and eventually cracked in hexagonal patterns -- the most efficient way to release tensile stress.

Tectonic forces then caused the 18 km wide cauldron -- along with the rock columns -- to tilt.

Cooled and solidified magma from the eruption now lies beneath Hong Kong's downtown areas along the iconic Victoria Harbor, said Denise Tang, one of the main contributors to the research and a geologist at Hong Kong's Geotechnical Engineering Office at the Civil Engineering and Development Department.

"Hong Kong's main city actually sits on a very old volcano, though people don't need to worry because the volcano's already extinct and it won't erupt again," Tang said.

The lead researcher, Rodrick Sewell, said the discovery might inspire more explorations in the southeast China region.

"This is the first well-documented example of a super volcano -- an ancient one -- in southeast China. But we suspect there are other hidden examples in south-east China that are yet to be discovered," Sewell said.

Sewell said he first came up with the super volcano hypothesis to explain Hong Kong's unusual geological structures one day while he was walking home in December 2008.

The conclusion of a super volcano came after years of meticulous geological surveying work, he said.

"I think for any scientist, it's the 'a-ha' moment, after years and years of painstaking, systematic research, you suddenly see the story come together. And that is very exciting, when it comes together that way," Sewell said.

Hong Kong's High Island Super volcano could be classified as a mid-sized ancient super volcano, Sewell added.

The world's last super volcano eruption took place in New Zealand about 26,000 years ago, according to the Geotechnical Engineering Office's handout.

The evolutionary split between apes and human beings took place about 5 million years ago, according to the Encyclopedia Britannica.