Eruptive fissures in Hawaii associated with Kilauea; what are they? What is really happening? 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?
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.