Eruptions

More signs of melting at Redoubt

Posted by Erik Klemetti on January 31, 2009
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The “eruption watch” continues at Redoubt … Saturday revealed that things are getting hotter at the summit near the 1989/1990 dome (see picture above that made Redoubt famous in 1989). The overflight of the volcano revealed new holes in the summit glacial and a multitude of muddy streams formed from the meltwater. This area of very intense fumarolic activity is just below the 1989/1990 dome (~7,100 feet) and has been growing over the past few days. They also report an area at ~9,000 feet on the volcano that shows signs of ice collapse, indicating heat from underneath the snow and ice (similar to what was seen at Mt. Saint Helens when it reactivated in 2004).

The Seattle PI article linked here does seem to get a little confused when it comes to the potential volcanic products at Redoubt. From the article:

“Geologist Jennifer Adleman said magma is a combination of three phases: liquid rock plus a gas and crystals than can form sort of a froth that works its way up the mountain.

“A lot of scientists refer to is as a crystalline mush,” she said.”

Now, I’m not certain what Adleman is referring to in her quote, but I’ve never heard of the frothy material as a “crystalline mush”. Not to say that is an inaccurate description, but usually mushes are referred to when the magma is at depth in the volcano. This is more like a foam, with the liquid and crystals entrained in a magma that is packed with bubbles that form as the magma decompresses. If those gases get bottled up before the volcano erupts, you could get an explosive such as what happened at Mt. Saint Helens in 1980. If not – if the gases are allowed to be more passively released, lets say if the magma stalls as it comes up – then we might get the toothpaste-style eruption we saw in the most recent Saint Helens activity.

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Comments

  1. #1 gg
    February 1, 2009

    Is it significant to see earthquake activity at Kamchatka, and off the east coast of Japan while Redoubt is firing up?

  2. #2 Magma-hydrothermal
    February 1, 2009

    The “crystalline mush” terminology seems to be a quite clear
    textural description of a liquid-crystal-gas material sloshing
    around in the throat of a volcano.
    Actually, the largest volumetric increase, or overpressure, accompanies
    the exsoution of water from the deeper magma-crystal material.

  3. #3 Erik Klemetti
    February 1, 2009

    I think what we’re seeing here is the problem with terminology. I tend to work in the deeper plumbing of magmatic systems – >5 km below the volcano – and in those circles, a “crystalline mush” or “crystal mush” refers to the leftovers of a magmatic batch when you have a high proportion of crystals (>50%) with liquid (magma) between the crystals. The material behaves more like a solid than a liquid and can even have a rigid network of crystals. You can think of it as a proto-granite (if it is the right composition) under the volcano that is made up of crystals (and liquid) that didn’t erupt.

    However, it sounds like the upper-level volcanologists have also taken the term for the crystal-liquid-bubble mixture that makes its way up the conduit during/before an eruption. Both uses are valid so it is really the context that counts.

    As for the gases, if the magma is allowed to degas at depth effectively – lets say there is a crustal feature like a fault or lineament that allows for degassing – then it is less likely to exsolve a lot of bubbles as it comes up the conduit. However, if it doesn’t degas at depth, then bubble growth can be quite rapid in the conduit at shallow levels and that is what produces the explosive eruptions we see.

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