This is very cool! It’s a movie showing the lava bubbling in the Halema’uma’u vent. Click here to watch it.

I see that I need to restate what I wrote in the previous post about gas pistoning, because it was incomplete. I plead vog, as usual, and for my punishment, I get more vog. Here is the complete explanation.

Magma in the Halema’uma’u vent is freely bubbling most of the time, as shown in this movie. The bubbling does eventually cause the pistoning effect, but there is more to it. Occasionally a thin layer of the surface cools and hardens (this is why the incandescence of the vent ‘winks out’ sometimes). The gas that causes the bubbling builds up pressure behind the thin top layer. Suddenly we have an explosive gas piston event that blows the top layer off, showering tephra (the technical term for all kinds of volcanic ejecta) as far as several hundred feet up to the floor Kilauea Caldera, which contains Halema’uma’u Crater.

Those blasts also continue to blow away material from the sides of the vent. So I also need to update you on the current dimensions of the Halema’uma’u vent. Today USGS released new information that tells us the vent has grown to about 215 feet across, more than double its size since it first appeared on the crater floor. A graphic comparison between the original size of the vent in April and today’s dimensions can be found here.

As a reward for those of you who have slogged through all the stuff above and stayed with me to the end of this post, here is a special nightshot movie of the explosive eruption at 8:13 PM on September 2. That eruption scattered lava rocks as big as 8 inches long all around the Halema’uma’u crater rim.