We knew that they said it was dangerous but until the real flows started to come down and take out houses and take out buildings and burnt out forests and all of these things, we didn’t really, until then we didn’t get a good grasp.
– Montserrat Resident, 2019
Pyroclastic flows are hot mixtures of gasses and tephra (volcanic rocks of micrometers to meters in size) that travel down volcanic flanks at high speeds of more than 100 km/h. At Soufrière Hills, pyroclastic flows typically form when the growing dome becomes instable and collapses. Large Vulcanian explosions in 1997 also produced pyroclastic flows when the eruption column lost momentum and collapsed.
Listen to how Montserratians experienced the first pyroclastic flows descending Soufrière Hills Volcano:
The video shows a pyroclastic flow descending Tyers ghaut. In the second half of the video you can see thermal images recording how hot the pyroclastic flow is. The red parts represent temperatures of more than 400˚C!