The newly identified supervolcano, which is thought to have been active in the first billion years of Mars' 4.5 billion year existence, could be one of a number at the time that caused this change.
The remains of the volcano were spotted in images of the Arabia Terra region of Mars. The terrain is heavily pitted with impact craters, but scientists studying images of a large circular basin called Eden Patera noticed it lacked the typical raised rim and splash marks beyond that come from asteroid strikes.
Instead the 52 mile wide and one mile deep basin had a series of rock ledges similar to bathtub rings that form after a lava lake slowly drains.
The basin is also ringed by faults and valleys that occur when the ground collapses due to activity below.
This led experts to suggest the basin is actually a volcanic caldera that caused when a large body of magma loaded with dissolved gas rose through the thin crust to the surface. This caused the supervolcano to blow its contents over a huge area.
"This highly explosive type of eruption is a game-changer, spewing many times more ash and other material than typical, younger Martian volcanoes," said Dr Jacob Bleacher, a volcano specialist at Nasa's Goddard Space Flight Centre.
"During these types of eruptions on Earth, the debris may spread so far through the atmosphere and remain so long that it alters the global temperature for years."
Eden Patera, one of several sites on Mars that may be the footprints of ancient supervolcanoes. Red colors are relatively high and purple-gray colors are low
The researchers, whose findings appear in the journal Nature, believe the massive eruptions may have been responsible for spreading the volcanic debris that is found elsewhere on Mars but have never been linked to a known volcano.
The scientists have identified a number of other candidate volcanoes in the area.
"If just a handful of volcanoes like these were once active, they could have had a major impact on the evolution of Mars," said Dr Bleacher.
Supervolcanoes are typically defined as a volcano capable of expelling more than 240 cubic miles of rock and ash should it explode.
The biggest known supervolcano eruption on Earth was when Lake Toba in Indonesia, which threw out 672 cubic miles of debris when it erupted approximately 74,000 years ago.
The La Garita Caldera in Colorado is thought to have ejected around 1,200 cubic miles of rock and ash when it exploded more than 27 million years ago.
Glen Coe in Scotland is also thought to have been formed as a result of a supervolcano explosion.
Joseph Michalski, a geologist at the Planetary Science Institute and Natural History Museum in London who was a co-author on the paper, added that their findings may now make it easier to identify other ancient volcanoes on Mars.
They used images taken by Nasa's Mars Odyssey, the Mars Global Surveyor and Mars Reconnaissance Orbiter along with ESA's Mars Express oribter.
Dr Michalski said: "On Mars, young volcanoes have a very distinctive appearance that allows us to identify them."
"The long-standing question has been what ancient volcanoes on Mars look like. Perhaps they look like this one."
via Science - Google News http://news.google.com/news/url?sa=t&fd=R&usg=AFQjCNGCYL--XnQ2Fcu545ViC1cbGiHa0w&url=http://www.telegraph.co.uk/science/10352062/Supervolcano-that-transformed-Mars-found.html
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