mummi

4.12.2014 | 11:40

Báðrðarbunga, big picture.

This is an English overview of this blog from the beginning of the Bárðarbunga event.

I do think this is a mix of both rifting and inflation. This starts with minor magma intrusions into the magma chamber of BB. This is possible to see by analysing data from before 16 August where BB is inflating. At this point, increased pressure in the magma chambers presses the caldera walls apart and the top up. This YouTube video suggests how this might happen mechanically.

Because Bárdarbunga sits between Eurasia and North America, this presses the tectonic plates apart, which probably had begun to pull significantly, because it had not erupted for a long time in this area. When summing up, a crack lying on the plate boundary opened up, now known as the dyke and magma started to leak (pressure fell in BB) into it. This dyke is a very big gap about 1 km^3 that occurred in the earth's crust in a few days. A strong indication that this is manly tectonic driven event is the lack of up and down movements of GPS stations recording the event.

System diagram

When pressure dropped in the hot rock, deep in the earth crust a large scale decompression melt must have started and expansion from it, is now a part of what is keeping the show running.

To fill the dyke, magma started flowing from the mantle and from BB magma chambers along with water and debris, and BB top started to subside. When this had been on fore few days the most powerful volcanic related earthquake swarm in recorded histories started in BB. Soon after, lava started running in HH as it has now done for 3 months.

The quakes under BB have wide range of appearance some look like sharing and cracking and other have look of explosive and collapsing and there is large bitt with a true look of magma intrusion, those have been on uptick from the start.

We can distinguish that the earthquakes that occur in the caldera fracture, move up and down in time. This can perhaps be explained by the "plug" (crust within the caldera) is broken and laminated with magma between the layers, building up what is referred to as top magma chambers. Density of the rock in the plug is higher than in the magma surrounding it and when unsupported by the caldera wall and pressure from the bottom magma chambers it will sink and put tension on the plug structure.

For almost a full month there were no quakes in the top 3 km of the caldera fracture. By the time the first quake occurred there, one can assume that the lower part of the plug, the part under the topmost magma cambers, had already started sliding down and magma from the lower chambers must have been drawn up to fill the void. This is also one way to explain all the energy release in shearing quakes related to the event and are hardly explained by the visual subsidence. If this is the situation, BB top magma chambers are getting fresh hot magma which is, and will be eruptible in future. Therefore I think speculations on top chambers being to solidified to erupt can be dismissed, (if it was to solidified it is not by now) however quantity of eruptible magma can be in the range of minimal to enormous.

This would mean that if HH stops erupting it will stop the visual subsidence, but not necessary the demolishing quakes at BB.

Today we can look at the situation as being “stable”, where magma flows from common source up to the top magma chambers of BB and out to HH. This could go on for some time, even years and then simply calm down.

However there is an ongoing risk of explosive event in the BB caldera and I believe that what is happening there now is part of process that can lead to big explosive event in the near geological future. (next 50k year).