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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 ...
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 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]
Pyroclastic flows cascaded down the mountain to the sea on all sides of the peninsula, wiping out the village of Tambora, and affecting a total area on land of about 874 km 2 (337 sq mi). [ 12 ] [ 13 ] A moderate-sized tsunami struck the shores of various islands in the Indonesian archipelago on 10 April, with a height of up to 4 m (13 ft) in ...
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]
Pahoehoe lava is a relatively smooth lava flow that can be billowy or ropey. They can move as one sheet, by the advancement of "toes", or as a snaking lava column. [10] A'a lava flows are denser and more viscous than pahoehoe, and tend to move slower. Flows can measure 2 to 20 m (7 to 66 ft) thick.
Temperatures as high as 850 °C (1,560 °F) [56] are known to occur in pyroclastic flows, which will incinerate everything flammable in their path, and thick layers of hot pyroclastic flow deposits can be laid down, often many meters thick. [57]
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.