July 31, 2008
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Halema`uma`u appears laid back but . . .In contrast to the spectacular incandescent explosions and springtime spatter showers at the Halema`uma`u Overlook in March and April, the eruptive vent at the summit of Kīlauea Volcano seems to have adopted a laid-back summer attitude, with a steady plume rising from a dull glowing hole at the base of the southeast wall of the crater.
The 40-meter-wide (120-feet-wide) opening of this still-fuming chimney provides a partial view into the bright abyss beneath the crater wall that broadcasts the clatter of frequent wall-rock collapses and extends to depths within earshot of splashing and sloshing magma.
During the spring 2008 eruptive period, this hot, gargling vent coughed up an interesting m?lange of "pyroclasts" - rocks, dust, and gravel from the collapsed crater floor and conduit walls, mixed with a small portion of bombs, spatter, Pele's hair, and tears that were molten or near-molten when erupted. (The latter fragments are referred to as "juveniles" in volcano parlance because they are first-timers at the earth's surface.)
Pyroclasts can tell us the conditions of their formation. For example, we know that the Pele's hair, tears, pumice, and glassy spatter are identical in composition to the hottest Kīlauea lavas recently erupted along the east rift zone. The composition of the gases from Pu`u `Ō `ō and Halema`uma`u are also similar to each other, showing that, after nearly 25 years of near-continuous volcanic eruption, magma pathways throughout Kīlauea's shallow volcanic edifice are full of new magma from depth.
Subtle clues as to whether the summit eruption will either cease or perhaps become ominously hazardous could be found through further study of the pyroclasts. We have found that a sordid lot of pumice-like glass fragments were, prior to their springtime expulsion from the vent, baked in a fumarole on the sides of the conduit, in a fashion akin to creosote build-up in a stove pipe. Collectively these and similarly recycled material are evidence for subterranean build-up of debris-talus and spatter deposits within the eruption conduit.
Close examination of spatter and large lava droplets (lapilli) reveals dense, relatively cool crystal-mush clots contained within hotter bubbly lava. This is a clear sign that cooler magma was disrupted by hot, effervescing magma prior to eruption.
For the past two months, there has been a scarcity of unquestionably fresh glassy material from Halema`uma`u. The plume is only lightly ash-laden, and newly formed glassy particles that are presently being erupted cannot be readily distinguished from previously erupted material plucked off the ground by strong winds.
Steady summit gas emissions and the small quantity of Pele's hair and tears being erupted indicates that summit magma may have temporarily receded or may no longer be as well-connected to the atmosphere. The Halema`uma`u chimney may be partially sealed by a mix of collapsed wall rocks and choked by recent deposits of lava spatter, pumice, bombs and ash. If magma stops moving within the conduit, it will cool and thicken into a partially molten plug resembling the springtime chunks of relatively cool crystal-mush.
The longer that plug cools, the more likely this recent period of summit activity will slowly come to a close. It is most likely that a balance will persist. A lava plug beneath a subterranean pile of talus and spatter would provide little resistance but plenty of explosion fodder for the next time fresh, hot magma rises beneath the Halema'uma'u Overlook and gas pressure builds up!
Kīlauea Volcano continues to be active. A vent in Halema`uma`u Crater is erupting elevated amounts of sulfur dioxide gas and very small amounts of ash. Resulting high concentrations of sulfur dioxide in downwind air have closed the south part of Kīlauea caldera and produced occasional air quality alerts in more distant areas, such as Pahala and communities adjacent to Hawai`i Volcanoes National Park, during kona wind periods.
Pu`u `Ō`ō continues to produce sulfur dioxide at even higher rates than the vent in Halema`uma`u Crater. Trade winds tend to pool these emissions along the West Hawai`i coast. Kona winds blow these emissions into communities to the north, such as Mountain View, Volcano, and Hilo. Incandescence continues to be observed at night inside Pu`u `Ō`ō and suggests minor activity from vents within the crater. There was a small explosion within the crater that deposited small rocks around the east rim of the cone; seismic and tilt data suggest that this occurred on the evening of July 26.
Lava continues to erupt from fissure D of the July 21, 2007, eruption but no breakouts have been observed in the past week on or above the pali. Lava, however, continues to flow through what remains of Royal Gardens and across the coastal plain to the ocean in a well-established lava tube, active now for several months. Minor-to-moderate explosive activity continues at the Waikupanaha ocean entry, and there have been a few new breakouts immediately inland from the delta. A small (2.5 acre) delta collapse that probably occurred between 5 and 6 a.m. on Wednesday, July 30, scattered large rocks up to 100 meters (yards) inland from the collapse scar.
Be aware that lava deltas could collapse at any time, potentially generating large explosions, as happened this past week. This may be especially true during times of rapidly changing lava supply conditions, as have been seen lately. Do not venture onto the lava deltas. Even the intervening beaches are susceptible to large waves generated during delta collapse; avoid these beaches. In addition, steam plumes rising from ocean entries are highly acidic and laced with glass particles. Check Civil Defense Web site (http://www.lavainfo.us) or call 961-8093 for viewing hours.
Mauna Loa is not erupting. Three earthquakes were located beneath the summit this past week. Continuing extension between locations spanning the summit indicates slow inflation of the volcano.
Two earthquakes beneath Hawai`i Island were reported felt within the past week. A magnitude-2.4 earthquake occurred at 00:55 a.m. on Saturday, July 26, 2008, H.s.t., and was located 2 km (1 mile) southwest of Kilauea summit at a depth of 2 km (1 mile). A magnitude-2.7 earthquake occurred at 12:20 p.m. on Monday, July 28, and was located 7 km (4 miles) southeast of Ho`okena at a depth of 14 km (9 miles).
Visit our Web site (http://hvo.wr.usgs.gov) for daily Kīlauea eruption updates, a summary of volcanic events over the past year, and nearly real-time Hawai`i earthquake information. Kīlauea daily update summaries are also available by phone at (808) 967-8862. Questions can be emailed to askHVO@usgs.gov.
Updated: August 1, 2008 (pnf)