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Pyroclastic flows sweep down the flanks of Mayon Volcano, Philippines, in 2018. A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) [1] is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of 100 km/h (30 m/s; 60 mph) but is capable of reaching speeds up to ...
The resulting deposits formed a fan-like pattern of overlapping sheets, tongues, and lobes. At least 17 separate pyroclastic flows occurred during the May 18 eruption, and their aggregate volume was about 0.05 cu mi (0.21 km 3). [9] The flow deposits were still at about 570 to 790 °F (300 to 420 °C) two weeks after they erupted. [9]
These can often climb over obstacles, and devastate human life. [2] Earthly pyroclastic flows can travel at up to 80 km (50 mi) per hour and reach temperatures of 200 to 700 °C (392 to 1,292 °F). The high temperatures can burn flammable materials in the flow's path, including wood, vegetation, and buildings.
The emplacement temperature range of the first surge was 180–220 °C (360–430 °F), minimum temperatures; of the second, 220–260 °C (430–500 °F). The depositional temperature of the first was 140–300 °C (280–570 °F). Upstream and downstream of the flow it was 300–360 °C (570–680 °F). [30]
Thermal sensing: The presence of new significant thermal signatures or 'hot spots' may indicate new heating of the ground before an eruption, represent an eruption in progress or the presence of a very recent volcanic deposit, including lava flows or pyroclastic flows.
Only Ruapehu was high enough to divert the flow. [8]: 128–9 The power of the pyroclastic flow was so strong that in some places it eroded more material off the ground surface than it replaced with ignimbrite. [8]: 225 There is evidence that it occurred on an autumn afternoon and its energy release was about 150 megatons of TNT equivalent. [6]
The ignimbrite phase is characterized by low eruption fountain, [11] but co-ignimbrite column developed on top of pyroclastic flows reached a height of 32 km (20 mi). [12] Petrological constraints on sulfur emission yielded a wide range from 1 × 10 13 to 1 × 10 15 g , depending on the existence of separate sulfur gas in the Toba magma chamber.
The mushroom-shaped plume rose from avalanches of hot debris (pyroclastic flows) that cascaded down the north flank of the volcano. Mushroom cloud from the atomic bombing of Nagasaki , Japan, on 9 August 1945