An explosive volcanic eruption in Chile has given scientists the first direct insight into the strange motion of rocky lava known as obsidian flow.
Rather than a red river of molten rock oozing down a mountainside, this lava is a thick, rubble-strewn mass of rock.
Dr Hugh Tuffen, from the University of Lancaster, and his colleagues took the first measurements of this lava flow.
They found that it kept moving more than a year after the eruption.
Their results were published in the journal Nature Communications.
Here Dr Tuffen describes the findings and what it was like to witness the giant volcanic eruption still in action.
Footage courtesy of Jonathan Castro, University of Mainz