The early-June eruption at Guatemala’s Volcan de Fuego, whose pyroclastic flows killed at least 109 people, may have slipped away from the headlines, but that doesn’t mean the story’s over for those still living there. While volcanologists on the ground use drones to get a better sense of the violent changes that have occurred, NASA’s Landsat-8 satellite is peering at the devastation from up on high.
As reported by Earth Observatory’s Adam Voiland, these images reveal quite remarkably clearly where the pyroclastic flow deposits are, but that's not all. Somehow, three weeks after the eruption took place, you can still detect these flow deposits' incandescent thermal glow from space.
How, then, is this possible?
Pyroclastic flows are types of pyroclastic density currents (PDCs), turbulent streams of fresh volcaniclastic material that are produced by explosive volcanic activity. Flows are the most common – mixtures of hot ash, gas, entrained debris and flecks of lava – and they can form in a variety of ways.
In terms of Fuego, it appears many were generated as a result of parts of the sustained column of ash, shooting skyward from the vent, lost upward momentum and fell back down to Earth. This could have been through a lack of explosive thrust at the vent, or sufficient cooling – and subsequent lack of buoyancy – in the ash column.
Some, however, may have formed as the vent “boiled over”, and essentially spilled volcaniclastic material right over the peak and down the slopes. Either way, pyroclastic flows quickly formed and rushed down the valleys on Fuego’s flanks.
Forget that notion of cooling-and-collapse though: these flows are still astonishingly hot, with internal temperatures ranging from 200-700°C (390-1,300°F), moving at 80 kilometers (50 miles) per hour, roughly speaking. Anything they touched was blown away; people were instantly scorched, and suffered from extreme heat shock or asphyxiation.
Death is inevitable for anyone caught up in a pyroclastic flow, but what happens when they come to a stop?