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    Question ID:   4532         Current Version: 1
Question: How hot is a volcano?
Category: Science > Earth Sciences
Keywords: hot, lava flow, pyroclastic, debris avalanch, lahar, temperature, volcano
Type: how
Rating:(0 ratings)    Views: 400    Discussions: 0   In Watch Lists: 1  

 
    Answer:

Lava and Lava Flows

  • The tube system (lava tubes) of episode 53 (Pu'u O'o eruption, Hawaii) carried lava for 10 kilometers (6 miles) from the vent to the sea. So efficient were the tubes in containing heat that lava cooled only 10 degrees Celsius across that distance. When it reached the ocean, the lava was still a sizzling 1,140 degrees Celsius (2,085 degrees Fahrenheit).
  • The temperature of the lava in the tubes is about 1,250 degrees Celsius (2,200 degrees Fahrenheit).
  • By way of its color, incandescent rock gives a crude estimate of temperature. For example, orange-to-yellow colors are emitted when rocks (or melt) are hotter than about 900 degrees Celsius (1,650 degrees Fahrenheit). Dark-to-bright cherry red is characteristic as material cools to 630 degrees Celsius (1,165 degrees Fahrenheit). Faint red glow persists down to about 480 degrees Celsius (895 degrees Fahrenheit). For comparison, a pizza oven is operated at temperatures ranging from 260 to 315 degrees Celsius (500 to 600 degrees Fahrenheit).
  • Lava sampling can be risky, so why do we bother to do it? Hot lava samples provide important information about what's going on in Kilauea's magma chambers. ... We know from laboratory experiments that the more magnesium there is in magma, the hotter it is. Chemical analysis therefore provides the means, not only to determine the crystallization history of lava, but also to establish the temperature at which it was erupted. ... Episode 54 lavas are chemically different from lavas erupted over the last 12 years. Chemical analyses show that magma was supplied by two distinct magma bodies that have resided for years beneath Napau Crater, where eruptions last occurred in 1983 and in 1968. Lava nearest Pu'u O'o erupted at 1,125 degrees Celsius to 1,130 degrees Celsius (2,057 to 2,066 degrees Fahrenheit) and contains crystals of olivine, feldspar and pyroxene. Calculations show the source of this lava was intruded at the beginning of the Pu'u O'o eruption in January 1983. The lava erupted from the west wall of Napau tapped a second magma body that was possibly emplaced in August 1968. This magma, which had been cooling and crystallizing for a longer time, erupted with more abundant feldspar and pyroxene crystals and at lower temperatures of 1,110 to 1,120 degrees Celsius (2,030 to 2,048 degrees Fahrenheit).
Pyroclastic Flows, Debris Avalanches, and Lahars
  • High-speed avalanches of hot ash, rock fragments, and gas move down the sides of a volcano during explosive eruptions or when the steep edge of a dome breaks apart and collapses. These pyroclastic flows, which can reach 1,500 degrees Fahrenheit (815 degrees Celsius), and move at 100-150 miles per hour, are capable of knocking down and burning everything in their paths.
  • Mount St. Helens, May 18, 1980: Emplacement temperatures of the debris avalanche ranged from about 70 degrees to 100 degrees C, and those of the directed blast ranged from about 100 degrees to 300 degrees C and varied with azimuth from the volcano. Emplacement temperatures of the pyroclastic-flow deposits ranged from about 300 degrees to 730 degrees Celsius (570 to 1350 degrees Fahrenheit), near-vent deposits were emplaced at about 750 to 850 degrees C.
  • Novarupta (Alaskan Peninsula) was the source of the world's most voluminous 20th-century eruption. The 60-hour eruptive sequence of 6-8 June 1912 included ... an 11-cubic kilometer zoned ignimbrite sheet filling the Valley of Ten Thousand Smokes ... The "ten thousand smokes" in the ash-flow sheet mostly died out by 1930, and the few fumaroles remaining today are odorless wisps that issue from Novarupta and from intravent fractures nearby. Although orifice temperatures were as high as 645 degrees Celsius (1,193 degrees Fahrenheit) in 1919, none are hotter than 90 degrees Celsius (195 degrees Fahrenheit) at present.
Source: USGS
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