Tuesday, July 19, 2011

Katla continues to develop toward an upcoming volcanic eruption

The Icelandic press is reporting that there are ponds collecting as the ice in the Myrdalsjokull glacier continues to melt from the increasing heat coming from the underlying volcano, Katla, in Iceland. (h/t Jón Frímann ).

Collapsing ice cap above Katla (Iceland Review – English, and Icelandic ) (Remember that the black cover is because of the ash from Eyjafjallajokull last year)

As the fractures from the earthquakes continue to fracture to the surface, so the paths that they create allow water to migrate down to the underlying hotter rock. This then converts to steam, and flows back up helping to further melt the underside of the ice sheet, with some water possibly escaping down the mountain, under the ice. These floods can be sudden, as was the one that took out the ring road around Iceland. That has now been repaired, a week after the flood took it out.

The narrowness of the fracture paths, at least initially, will slow magma migration and this will likely allow more additional activity at the surface, although Katla does not give a lot of warning before it erupts, apparently.

One of the misfortunes of having retired and given away many of my books is that I no longer have the references that relate quake size to rock damage. A lot of this work was done in the South African gold mines, which go down over 3 km (2 miles) and are thus at the depths of many of the current quakes around Katla. As the mines extended the workings so the weight of the surrounding rock shifted, and the speed of this (usually following a mine blast with explosives that broke out some rock) would cause rock fracture in the area.

Quakes could be created that were up to a magnitude 4, similar to some of those around Katla recently, and resulted in significant rock movement and fracture. Underground this leads to problems with keeping the tunnels open and safe for the workers (since the rock bursts can be violent and hurl rock fragments a long way, as well as creating air blasts that can also be dangerous). There have also been larger ones.

But I was trying to get some sense of displacement and damage as a function of seismic strength, since when the rock fractures there is often some crushing of the rock along the interface of the fracture, and this would then be removable by the upward pressure of magma, and the fractures released the overlying confinement. The initial crushed zone probably measures just a few inches, but will be eroded out by water/steam passage and the later passage of magma, since fractured rock is easily removed. This then gives the open passages for magma to move. If the fractures intersect then the intervening rock will likely also be removed since the magma has a higher density and thus more power than mere water or steam flows. There have now been several dozen quakes within the region of the Katla caldera, and knowing the damage zone from each would allow a better estimate of how damaged the rock is. Bear in mind that the re-healed fractures (healed by cooling magma) from earlier eruptions are likely the weakest links that are now failing and opening, and in the process, therefore rebuilding the network of passages that are needed for flow. The levels of permeability generated are orders of magnitude greater than that from a typical oil well.

Where the rock is attached to the overlying ice, then cracks in the rock can also occur in the overlying ice. And you may note that in the above picture apart from the circular rings of fractures, there are three well defined line cracks that cross the circular fractures. If you also look at the web cam you can see (in daylight) some of the lines where magma has flowed up to the surface in earlier eruptions (the picture shown in the last post).

So we now watch as the process continues to unfold.


  1. thank you for the interesting information about Katla.
    I have a question.. maybe a silly question :)
    I see how the magma try to break through rocks, and how the heat has effects on ice. But my question is, how much can a glacier big as Myrdalsjokull cool the magma?
    can the glacier's ice cools down the magma and even stop a small eruption?

  2. The water/ice that the magma meets as it leaves the rock controls how the magma fragments. Generally it breaks into fine ash under the thermal shock, and the amount of water/ice controls how fine this ash is.

    Th finer ash is carried further and can cause problems in European airspace. The water coming into contact with magma within the rock causes the water to change to steam and this rapid expansion can help blow the overlying passage ways clear of obstruction actually making it easier for the magma to escape.

    In relative terms the ice cap is too thin to freeze the magma, that only occurs where the water volumes are very large (such as when the Hawaiian lava flows into the sea).

  3. could the advanced techniques of seismic imaging used to visualize the extent of oil reservoirs be used to visualize, in a time series, the changes in magma movement, or is the contrast and/or resolution too low?

  4. I think that it is more that no-one would be that excited about getting the geophone arrays close enough to get a good signal, given that the whole top of the glacier might get blown off in an eruption.

    I would think that with enough computing power it should be possible to plot magma migration in theory, but in practice there may be enough other extraneous noise at that point in the unfolding event that it would start to become hard to filter out that signal alone.