Mt. Pinatubo Eruption. Photo by Albert Garcia taken on June 15, 1991 // A volcano's deadly pyroclastic flow - the same thing that buried Pompeii. You can't outrun it: it travels at 700 km/h (450 mph) and you can't weather it in anything but highly specialized shelters: it's over 1,000 °C (1,830 °F). Once you see that in your rear view mirror, you're either already out of reach or you're not.
Must go faster! Volcanic pyroclastic flow, a fast-moving current of superheated gas (which can reach temperatures of about 1,000 °C (1,830 °F)) and rock (collectively known as tephra), which reaches speeds moving away from a volcano of up to 700 km/h (450 mph).
The dome of Unzen, Japan Volcano collapsed and created a pyroclastic flow in '91. The people here escaped when the flow stopped before reaching them, but the deadly and terrible speed of it, is astonishing. Pyroclastic flows are fluidized masses of rock fragments and gases that move rapidly in response to gravity. They can form in several different ways, such as when an eruption column collapses, as the result of gravitational collapse or from an explosion on a lava dome.
This area in New Mexico owes its remarkable geology to layers of volcanic rock and ash deposited by pyroclastic flow from a volcanic explosion. Over time weathering and erosion of these layers has created canyons and tent rocks. The tent rocks themselves are cones of soft pumice and tuff beneath harder caprocks, and vary in height from a few feet to 90 feet.
Pyroclastic flow will destroy nearly everything in its path. With rock fragments ranging in size from ash to boulders traveling across the ground at speeds greater than 80 km per hour, pyroclastic flows knock down, shatter, bury or carry away nearly all objects and structures in their way. The extreme temperatures of rocks and gas inside pyroclastic flows, between 200°C and 700°C, can cause combustible material to burn, especially petroleum products, wood, vegetation, and houses. -- Samuel…