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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 ...
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.
An ash flow from this explosion was recognised 2,500 km west of the volcano. The total area of recognisable pyroclastic fall was greater than 800,000 km 2. The pyroclastic ash encircled the globe in 13.5 days and at altitudes of between 30 and 50 km the average velocity was 12 km/h. The ash remained in the upper atmosphere and produced ...
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]
The following Pelean phase produced pyroclastic surges of molten rock and hot gases that reached as far as Misenum, to the west. Concentrated to the south and southeast, two pyroclastic surges engulfed Pompeii with a 1.8-metre-deep (6 ft) layer, burning and asphyxiating any living beings who had remained behind.
The study of the causes of the disaster marked the beginning of modern volcanology with the definition and the analysis of the deadliest volcanic hazard: pyroclastic flows and surges, also known as nuées ardentes (Fr: burning clouds). Eruptions of a similar type are now known as "Peléan eruptions."
A wide variety of volcanic processes can produce tsunamis. This includes volcanic earthquakes, caldera collapse, explosive submarine eruptions, the effects of pyroclastic flows and lahars on water, base surges with accompanying shock waves, lava avalanching into the sea, air waves from explosive subaerial eruptions, avalanches of cold rock, and avalanches of hot material. [1]
The most important characteristic of a Peléan eruption is the presence of a glowing avalanche of hot volcanic ash, called a pyroclastic flow. Formation of lava domes is another characteristic. Short flows of ash or creation of pumice cones may be observed as well. The initial phases of eruption are characterized by pyroclastic flows.