The VC Bar

Welcome to the Volcano Café bar, a place for all things on or off topic and inane ramblings. There has been a need of late to find a place better suited to various theories, long comments and enthusiasm. This page will be less moderated than the main article pages and cleared out every month (this may change depending on use).

Have fun and don’t forget to tip the barman 😉

1,846 thoughts on “The VC Bar

  1. Need to pick some brains:

    I’m sorta working on deep background for a SciFi story, set on an earth-like planet currently deep in ice-age. Far less oceans & seas than our ~70%, think ‘Great Lakes’ / Caspian-type hydrology, so ice-caps’ spread stalled for lack of water. Instead, permafrost & tundra down to ~35º N/S, boreal to ~ 20º N/S, give or take. Then mostly-arid ‘High Plains’ to low latitudes…

    The would-be settlers were promised a global inter-glacial, are NOT amused…

    That aside, do we *need* oceans to make plate tectonics as we know it work ?

    There’s the fluids cycle, from trench to volcanism, of course, of course.
    IIRC, the only *rapidly* spreading dry-foot ridges are in Iceland and E-Africa, the latter around Afar.
    Likewise, there seems no land-based equivalent of subduction trenches. IIRC, Death Valley, Dead Sea etc are ‘pull apart’ features as passing plates side-swipe. Similar densities mean colliding ‘continental’ plates tend to pile up until they erode or de-laminate…

    My preliminary take would be scattered intra-plate-type plume volcanism, akin to Tibesti Massif. Tall enough for snow-cap, so permanent springs & streams…

    The would-be settlers are now eyeing a large, mostly-dormant, breached caldera. There are some hot springs, with potentially useful geo-thermal mineralogy. The crater-lake’s spill-valley’s sun-facing slope is distinctly milder than most of the surrounds. There are convenient non-volcanic springs. Mid-level terraces are safely above bottom lands’ floods and fogs, yet some-what sheltered from prevailing wind…

    Thoughts ??

    • Katabatic wind might be a significant hazard. Antarctica might be a good reference for your geologic reference. There are many volcanoes under it’s ice that have only recently been discovered. I think the last press release was something like 91 previously unknown ones.

      Don’t forget that Tuyas form from icebound volcanoes.

    • Effectively, it is a Venus with a better climate. Or Mars, also with a better climate. You may get plate tectonics: whether water is needed for that is far from certain. If so, you will have mid-ocean ridges but far above any water, with deep-lying oceanic plates around them. Quite infertile. You will also have higher-lying areas build by silicic volcanism and plumes, similar to our continents, perhaps 4 km above the ocean floors (a bit less than on earth because of the lack of oceans) Subduction volcanism would be hindered by a lack of water. On the other hand any water there is will collect in the subduction trenches so the subducting plate will carry some water. Plume volcanism will occur as on earth. They will push up big bulges (as in Yellowstone) but it will be very cold on top – not ideal for living on. A rift valley might be perfect. Something like the east-african rift: kilometers deep compared to the bulge (warmer and a denser atmosphere), rivers coming down the slope from the glaciers on top, and some thermal heat.

      Do look at the atmosphere. If the scale height is like earth but the oceans are mostly dry, you may end up with rather thin air on the continents, similar to that on top of Mauna Kea. (Think the harandra of Malacandra.) This is another reason to prefer a rift valley.

      • Mars is too small for tectonics
        It have lost too much internal heat

        The litosphere on mars is very thick

        But mars is still warm inside, and may erupt once ever 50 million years.
        Some flows on Mars are very young looking

        • You say Mars is too cold and Mars is still warm inside… Mars has a stagnant lid but so does Venus. The lid actually insulates very well and this keep Mars from cooling too fast. Whether the mantle of Mars is convective is something we will find out once there are more seismographs.

      • Mars is warm inside
        But not as warm
        as Earth is inside.

        But have cooled too much, for frequent volcanism and tectonics.

        Mars is a smaller body and have cooled more and its not tidaly heated.

        Mars cooling rate is between Earth and our Moon

  2. Weird double drop of pressure at the summit of Kilauea, it is the first time I see this happening, DI events deflate the summit once, not twice, and the second drop is also strangely rapid. It is also preceded just about 15 minutes before or so by a drumbeat swarm with about 120 LP events (shallow depth), I doubt that is coincidence.

    There were also 2 deep tremors yesterday (presumably from Pahala) at 19:26 and 22:15 UTC.

      • Since a month or so, the flat minima during a DI event have been ‘humped’ with a small increase followed by a decrease midway through the minimum. Today’s weird sudden collapse happened at about the point where it would have had this increase. Did something collapse? Let’s see how the recovery goes. The DI events now seem to communicate with the magma near Pu’u’O’o which shows pressure increase when the DI curve at Kilauea are steepest (both during the decline and recovery). My guess is that the cause for today’s collapse is somewhere on the rift zone.

        Did the cameras show anything?

    • It has now recovered from the DI event, but stabilized down from the previous peaks, by about the amount of collapse.

  3. Grimsvötn is very Intresting now
    The ice in the South Caldera is melting
    And have acually melted alot since 1998. Since 2011 melting in the wall have increased alot.

    Geothermal activity have increased enormously after 2017.
    Now There is a warm open pool at the calderas rim, thats warm to scalding hot in places. Its heating up

    This is shallow magma thats constantly accumulating and exciting the geothermal systems.
    The uppermost magma chamber is told to be around 50 km3 in volume
    And be feed by an open conduit – dyke from below.

    • A key piece of evidence in Sigmarsson’s talk was the concentration of the element thorium in samples of ash and pumice from each Grímsvötn eruption of the 20th century. These show an increase in Th concentration over time. This suggests that they all came from the same source beneath the volcano (the magma chamber), where growth of crystals of low-Th minerals results in an increase in concentration in the remaining melt. This melt was erupted in each of the events that produced the samples e.g. in 1998 or 2004, and was probably left over from the huge Laki eruption in 1783. The Grímsvötn 2011 samples contain much less Th than previous eruptions. This implies that it is a different magma: hotter, richer in gas, and closer to the composition of the original melt that formed in the mantle.

      • Jesper, when you give text from someone else, can you please specify where you took it from? I believe this was copied from all-geo.org

        • I forgot …
          Its me thats dementia 😉

          Yes forgot to
          Copy that adress and notice

  4. Given much of the porous caldera wall material will be threaded and bound by permafrost, will a skewed thaw affect stability ??

    Yes, Mt. St.Helens, I’m thinking of YOU !!

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