Eruptions

The Halema'uma'u Crater at Kilauea on June 29, 2009, prior to a rockfall on June 30th that has blocked the vent. Image courtesy of HVO.

There is a bit of a buzz today about significant rockfalls that occurred in Halema'uma'u Crater at Kilauea on June 30th. Some articles have suggested that the rockfall has "snuffed out" glowing vent in the Crater. Well, this is partially true. HVO is reporting that the glow that has been seen at Halema`uma`uma has been, in fact, gone since the rockfall. Here is the report of the event:

A sequence of rockfalls, some quite large, within the Halema'uma'u vent at the summit of Kīlauea Volcano began at 1:38 p.m. H.s.t on June 30, 2009.
The initial rockfall produced a seismic signal equivalent to a magnitude-2.4 earthquake and was felt at the Hawaiian Volcano Observatory (HVO) and the adjacent Jaggar Museum. A nearby scientist heard the beginning of this rockfall followed by a loud
explosion. The normally white gas plume turned a thick brown for several minutes; later collection confirmed an increase in tephra entrained in the plume with at least one later dusting.

So, it seems that the vent has become clogged with debris from this rockfall, some of which may have interacted with the magma in the vent (thick brown ash plume). The rockfall itself may have been triggered by draining of the magma in the vent, but it was big enough to generate a M2.4 earthquake. Later observations since the rockfall seem to confirm the idea that the vent is blocked with debris:

Aerial observations yesterday morning, and views from the ground with a thermal camera last night, confirmed that the throat of the vent in Halema`uma`u crater had been choked with debris from Tuesday's collapses. By late yesterday afternoon, sporadic gas jetting sounds from the vent were heard by geologists on the rim of Halema`uma`u Crater. Overnight, the Webcam on the rim of Halema`uma`u Crater recorded a few points of incandescence, waxing and waning in brightness, deep within the vent.

Now, before everyone gets all excited that the "vent is blocked" and waits for an explosion, remember that Kilauea has a long history of lava from the crater region draining to vents on the flanks, so magma in the vent that is being blocked could very well merely drain from the summit to the flanks of the volcano. Also, the event might have been triggered by the fact that magma is draining from the summit in the first place. There is still magma under the collapsed region as the gas jetting sounds and points of glowing might suggest, but how the magma will react to its newly closed vent is hard to tell. It wasn't erupting from the Halema'uma'u Crater before the rockfall and gases are still able to escape, so [SPECULATION] any fears of pressure from behind the blockage are likely unnecessary [/SPECTULATION]. However, saying the vent is "snuffed out" in any way is premature (it might have been the product of the HVO Press Release titled "Glow From The Halema`uma`u Overlook Vent Snuffed Out by Collapse"), but rather there is enough material in the vent to block any light from the hot magma.

{Hat tip to Eruptions readers Anne Carrington Cotton and David for links for this post.}