A pyroclastic surge is a fluidized mass of turbulent gas and rock fragments which is ejected during some volcanic eruptions. It is similar to a pyroclastic flow but contains a much higher proportion of gas to rock, which makes it more turbulent and allows it to rise over ridges and hills rather than always travel downhill as pyroclastic flows do.
Pyroclastic surges are much faster moving than pyroclastic flows, and can reach speeds of 1050 km/h. Pyroclastic flows may generate surges. For example, the city of Saint-Pierre on the Caribbean island of Martinique in 1902 was overcome by one.
Base surge was first recognised after the Taal Volcano eruption of 1965, where a visiting volcanologist recognised the phenomenon as congruent to base surge in atomic explosions. The USGS defines base surge as turbulent, low-density cloud of rock debris and water and (or) steam that moves over the ground surface at high speed. Base surges are generated by explosions.[1]
Hot surges contain gas and steam at temperatures above 100 °C (212 °F) and are ejected from the vent. They may be as hot as 800 °C (1500 °F) and are produced by the same mechanisms as pyroclastic flows. Cold surges contain gas mainly below 100 °C (212 °F) and can be produced when magma comes into contact with a large volume of water (for example, if the vent is under a lake or the sea).
Surges can travel around ten kilometres and are enormously destructive because of their massive kinetic energy and, for hot surges, the lethally hot gas. Even cold surges can contain large quantities of toxic gases, such as hydrogen sulfide.
See also
References
 |
This volcanology article is a stub. You can help Wikipedia by expanding it. |
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
