July 9, 2009
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
The show goes on at Kīlauea's summit vent
Scientists were treated to views of active lava within the vent, about 280 m (920 ft) beneath the rim of Halema`uma`u. The lava could also be seen on a Webcam located at the closed Halema`uma`u visitor overlook (http://hvo.wr.usgs.gov/cams/HMcam/). Camera and visual observations showed that lava was spattering and upwelling on the northeast side of the vent, flowing to the southwest part of the vent, and sinking back down into the volcano. This convection—a subject of previous columns—may explain how fresh magmatic gas is constantly brought to the surface and released from the vent.
On June 30, everything literally went dark. That afternoon, at about 1:30 p.m., H.s.t, staff and visitors at both the Hawaiian Volcano Observatory and the Jaggar Museum of Volcanology felt the ground shudder as a booming sound emanated from the summit vent. A few seconds later, the eruption plume turned dark brown with ash. The seismic record from that time indicated that a large collapse—probably of the vent wall above the lava surface—had occurred.
During the next three-and-a-half hours, there were over 30 additional collapses. Many of these were felt, heard, and seen (as brown plumes of ash), but most were detectable only by seismometers. At 2:30 p.m., a large portion of the vent rim collapsed, enlarging the opening of the summit vent by about 40 percent. The opening now has an area of about three acres—the size of many land parcels on the east side of the Island of Hawai`i!
The behavior of the summit eruptive vent changed drastically following the collapses. Most obviously, there was no glow from the vent because the lava surface was completely covered by collapse rubble. Seismic tremor—seismic noise generated by the volcano—and gas emissions both dropped to their lowest levels since before the summit eruption started. The summit plume became thin and lazy, and the typical sounds of gas rushing stopped completely.
Two days after the collapses, the lava, gas-rushing sounds, and weak glow returned. The wispiness of the plume allowed for excellent views of the lava surface with the naked eye, and photos and video footage showed weakly spattering lava, again in the northeast side of, and deep within, the vent (see http://hvo.wr.usgs.gov/multimedia/images.html). A summit tilt event began on July 4, however, and the lava disappeared once again, along with the gas-rushing sounds and glow.
The next act in Kīlauea's summit eruption performance is difficult to forecast. In December 2008, similar conditions of low gas emissions, no glow, low tremor, and a wispy plume also existed, prompting some Hawaiian Volcano Observatory scientists to speculate that the summit eruption was over.
Of course, the vent reenergized itself in January, and the eruption continued. Based on that example, we don't expect that the current lull signifies the end of the eruption. Instead, the collapses of June 30, coupled with the recent summit tilt event, seem to have disrupted the magma plumbing system beneath Halema`uma`u, which had become well-established by early June. It may take days or even weeks, but the plumbing will probably reestablish itself, and we can expect the show to go on.
Kīlauea's summit eruption shows no signs of stopping and continues to surprise and impress us with its activity. If you missed the past month's performance, we invite you to visit the Hawaiian Volcano Observatory Web site to browse the descriptions, photos, and movies of the activity, and to stay tuned for the next act, which will surely follow the current intermission.
Kīlauea Activity Update
Surface flows in the Royal Gardens subdivision slowed early in the week in response to a deflation-inflation (DI) event at Kīlauea's summit last weekend. The flows had picked up again by mid-week, but another DI event, which began late on Wednesday, July 8, will have likely caused the flows to slow or stagnate again by this weekend. At the coast, the Waikupanaha and Kupapa`u ocean entries fluctuated in response to the DI events but remain active as of this writing (Thursday, July 9).
The vent at Kīlauea's summit was dark and quiet all week, producing only a very small quantity of rock dust from frequent small collapses of the vent walls. The plume has been thin and wispy, and volcanic gas emissions have been relatively low. They are, however, still elevated above background levels, resulting in high concentrations of sulfur dioxide downwind.
One earthquake beneath Hawai`i Island was reported felt this past week. A magnitude-2.8 earthquake occurred at 9:58 a.m., H.s.t. on Friday, July 3, 2009, and was located 6 km (4 miles) northwest of Pohakuloa at a depth of 36 km (22 miles).
Visit our Web site (http://hvo.wr.usgs.gov) for detailed Kīlauea and Mauna Loa activity updates, recent volcano photos, recent earthquakes, and more; call (808) 967-8862 for a Kīlauea activity summary; email questions to askHVO@usgs.gov.
Updated: July 29, 2009 (pnf)