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.
Pyroclastic flow sweeps down the side of Mayon Volcano, Philippines, during an explosive eruption on 15 September 1984. Note the ground-hugging cloud of ash (lower left) that is billowing from the pyroclastic flow and the eruption column rising from the top of the volcano. Credit: Photograph by C. Newhall on 15 September 1984.
Mayon Volcano, Philippines: Pyroclastic flow is a fast-moving current of hot gas and rock (collectively known as tephra), which reaches speeds moving away from a volcano of up to 450 mph. The gas can reach temperatures of about 1,830 °F. Pyroclastic flows normally hug the ground and travel downhill, or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope. They are a common and devastating result...
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.