10 comments on “Volcanoes as heat engines

  1. Thank you agimarc! Makes me wonder how, in cold, cold space, the temperature of a comet can heat up enough to vaporize water? It’s not as if a comet like 67P/C-G. had an atmosphere to keep the heat in, and I read it is 4 times further away from the sun than Earth. So, where does the heat come from, or rather, how is it kept and accumulated in the rock?

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    • Howdy Granyia – the heat comes from sunlight. The albedo of comet surfaces is soot black, kind of like tar without being shiny. It retains heat rather than reflects it off. So as the surface heats up and the heat percolates its way downward into the body of the comet, melting pockets of ice on the way down. This is not primarily water ice. Rather it is a mixture of ammonia, CO2 (-79 degrees C), CO (-191 C), CH4 (-161 C). Start mixing ices with salt, and the boiling point drops way down.

      The jets on 67P/C-G appear to come from circular pits. Layering is observed on the walls of the pits. Looks like jets blast out the pits. The ESA Rosetta web site has extensive photos.

      There is also a bit of a thermal lag on the jets, as they don’t take place as soon as the area is illuminated. They wait a while and taper off after the area rotates into darkness. Rotation period of 67P is around 12 hours, though it changes with the action of the jets.

      Here on earth, there is a thermal lag observed particularly in the temperate parts of the world of about 6 weeks. This is why the hottest days of the summer are in July and early August rather than on 21 June. Same thing happens in winter with late January to early Feb being coldest. Works the same way with comets, with most vigorous jet action being shortly after perihelion. Comets are smaller, so there is less thermal lag. Earth is a pretty large and complex system. Cheers –


      • Yeah… but on the ESA Rosetta web site they say that the jets are primarily H2O and CO2, that was what made me think it needs a helluva lot of heat to produce such powerful jets of steam. With powerful i mean shooting straight up as seen in the images. When the sun warms our soil it just steams weakly, and we are so much nearer to the sun, and have an atmosphere.


  2. Páll Einarsson in a post about the the tilt changes at Hekla: “What is happening at Hekla Volcano?” (30/06/2016)

    The tilt changes at Hekla volcano reflect a steady increase in magma pressure beneath the volcano for the last three decades, except during the eruptions of 1991 and 2000 (vertical lines on the graph) when the pressure dropped. Graph made by Erik Sturkell.


  3. News from Klyuchevskoy (Kamchatka): The eastern slope of the volcano is undergoing changes: at the hight of ~4500m a new crater has opened of about 500m in diameter, with powerful lava flows gushing down for two kilometers from it. Activity in the summit crater also continues with lava bombs shooting up to 600m high and a cinder cone growing inside, making the tall volcano still a few meters higher.



  4. Turrialba (CR): The results of an ash analysis today say it contains 10% of juvenile material, meaning fresh magma is near the surface. So, a “wet” eruption might be in the pipes…


  5. Pingback: An Introduction to Lunar Volcanic Activity |

  6. Pingback: The Geysers of Enceladus |

  7. Pingback: Introduction to Volcanic activity on Mercury |

  8. Pingback: The Nitrogen Geysers of Triton |

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