Scientists have produced a new map of the Moon's most unusual volcano showing that its explosive eruption 3.5 billion years ago spread debris over an area much greater than previously thought.
A team of astronomers and geologists, led by experts at Durham University, UK, studied an area of the lunar surface in the Compton-Belkovich Volcanic Complex.
By mapping the radioactive element thorium which spewed out during the eruption they discovered that, with the help of the Moon's low gravity, debris from the unnamed volcano was able to cover an area the size of Scotland, or around 70,000 square kilometres.
The eruption, which happened 3.5 billion years ago, threw rock five times further than the pyroclastic flow of molten rock and hot gases that buried the Roman city of Pompeii, the researchers added.
The research used data from NASA's Lunar Prospector spacecraft which first spotted the volcanic site in 1999 when it detected an isolated deposit of thorium on the Moon's far-side between the Compton and Belkovich impact craters.
Since its discovery, the deposit had been hard to study because it is hidden beneath debris from meteorite impacts, but Lunar Prospector did detect gamma rays emitted by the thorium that can pass through up to a metre of rock.
Based on this information, the team used a "pixon" image enhancement technique to sharpen the map and reveal the enormous size of the thorium deposit from the volcanic eruption.
Lead author and Durham University PhD student Jack Wilson said he was surprised by the gigantic scale of the explosion.
"Volcanoes were common in the early life of the Moon and in fact the dark 'seas' you can observe on the lunar surface were created by runny, iron-rich, lava that flooded large areas, filling in impact craters and low-lying ground," said Wilson.
"Eruption of viscous, light-coloured, iron-poor, lava, which creates steep-sided volcanic cones, was rare and observed only at a handful of sites such as this one. The explosive eruption of such lava is unknown elsewhere on the Moon, making this volcano unique," Wilson said.
"By mapping the radioactive content of the lava from this volcano we have been able to show that molten, radioactive rock was thrown far beyond the slopes of the volcano, reaching several hundred miles in one direction," Wilson added.