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I hear news of "eruptive lava fissures" opening up in Hawaii, nine of them at last count. But I don't understand what these are really.

Are these existing, older lava tubes that are suddenly opening to the surface due to recent filling with new lava, or cracks that go through the crust to to deeper chambers of magma, or something else?

update: I've just seen a the video in the CBS News website's Kilauea volcano eruption: Seismic activity increases, earthquakes strike 5 days in a row (scroll down for this particular video). I wonder if there is a better or more technical visualization of the sources for the fissures somewhere?

enter image description here

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It can be either an eruption from the top of an existing tube or deep surface cracks opening up existing magmatic systems. I believe, from what I've been hearing in the news, that in this case they are in fact fresh fractures, tectonic in origin, that have relieved local over burden and allowed magma to rise to the surface in areas that had previously been dormant for an extended period.

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  • $\begingroup$ this answer could be even better if you post some sources or some links to more information about this incident. $\endgroup$ May 8, 2018 at 6:38
  • $\begingroup$ @trondhansen Sorry I would but like I said all I have is secondhand reports and no time to do any meaningful research right now. $\endgroup$
    – Ash
    May 8, 2018 at 10:12
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Looking the diagram you supplied in the question, at the bottom there is graphical representation of a cross section through a volcano. The structure in red represents the magma conduits. Magma is simply molten rock that has not reached the surface, when it does, it no longer is called magma, but lava.

During a volcanic eruption, magma within the conduits is under pressure and it exerts pressure on the walls of the conduit - as can be explained by fluid mechanics.

Where there is a weakness in the wall of the conduit pressurized magma exits the conduit. If the pressure of the magma is large enough, the release of magma can itself be forceful. If the overlying rock is doesn't have the strength and/or flexibility to contain the contain the injected magma the overlying rock can form a fissure through which magma can erupt on the surface as lava. Hence, such occurrences are called lava fissures.

Something similar happens anatomically when arteries become weakened and can no longer withstand the pressure of blood within them and an artery ruptures, as occurs with ruptured aortas.

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