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REPORT ABUSIVE REPLY
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Best El Hierro Thread On GLP - Canary Islands - ACTIVITY HAS RETURNED - AGAIN!
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Anonymous Coward |
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[ link to volcanocafe.wordpress.com] Volcanic says:
March 29, 2013 at 19:26
A bit of geological fiction (or not?)
Imagine you want to push a whole volcano up. Now imagine that, instead of a typical, conical volcano, the volume is more complex and globally looks like a triangle, like, for instance, say, El Hierro.
If you mentally divide a island like that using a North/South line, it is obvious that the amount of mass in the West part is much less than the amount of mass in the East part. Take into account that the overall high is 4 km above the see bottom in the area. This is a lot to move.
If then the pressure centre is near the centre and a bit westwards from this N/S line, then it is probable that the West part will move more than the East part. Less mass in this area means it is “easier” to move. After a certain time, it is probable that a break-up will occur, around that North/South line, with lots of earthquakes, then propagating outwards. Now, if the West part continues to go up faster than the East part, a constraints field will start to build-up, and after a while this constraints field will need to be relaxed.
This new activity will start where the constraints are maximized, so near the centre of pressure. Then, this will propagate outwards. For an analogy, try to bend a plank of wood, you’ll see cracks occurring. This cracks can happen everywhere, but will preferentially occur near a point of previous failures.
Now, the triangular shape is supposed to be a triple-junction set-up, and one branch extends in the North-West direction. So, cracks will propagate in that direction.
After a while, the cracks will reach a distance where the field of constraints no longer propagate outwards, but rather propagates laterally at the same distance from the pressure centre.
However, there are less pre-existing failures because now the activity is moving outside of the old failure area. The constraints needed to break the rocks are higher, and instead of frequent, but lower intensity earthquakes, you get less frequent, but more powerful ones.
By the way, magma is probably following the cracks…
Sounds familiar?
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