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Volcanowatch

May 29, 2008

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


The rooftop view at Pele's house is magnificent

The Halema`uma`u plume rises over Crater Rim Drive. View from Keanakakoi.
The Halema`uma`u plume rises over Crater Rim Drive. View from Keanakakoi.
Since March 12, when a billowing cloud of fume erupted from the east wall of Halema`uma`u, thousands of Hawai`i residents and visitors have gazed out across Kilauea caldera to the site of the new vent. Its mesmerizing presence in the day and warm glow at night have captured the imagination of numerous photographers.

The spectacular discharge of volcanic gases and, to a lesser extent, ash and other tiny particles has also commanded the rapt attention of county, state, and federal officials concerned for the health and safety of island residents living downwind. Still others are visiting the eruption virtually; the HVO Web site recorded 1.3 million hits in May on the new vent Webcam alone.

For the HVO staff and other volcanophiles, much of the fascination is in trying to unravel this new mystery. While Kilauea is arguably one of the best-studied volcanoes on the planet, there is much about it that we still do not know. With the current eruptive situation, we are perched on Pele's roof, trying to understand what is going on inside by watching the chimney and listening very carefully to the sounds coming from within the house. One of the most elusive puzzles right now can be summarized in a single straightforward question: What specific volcanic processes are responsible for the remarkable glow and copious gas release that we are all witnessing at the new vent?

The answers have been emerging on the surface, so to speak. In late December, gas emissions started to increase. By late January, gas emissions switched from a deep, degassing chemical fingerprint to a shallow, eruptive one. Kilauea's eruptive gases characteristically have a high sulfur dioxide and water content and are comparatively low in carbon dioxide. Last fall, summit tremor, the constant, low-level shaking of the ground beneath Halema`uma`u, started increasing in mid-November.

On March 12, a month-and-a-half later, the new vent emerged. And a week beyond that, the first of three small explosions occurred. Ejected material initially contained ash and older reworked lithic material. More recently, fresh Pele's tears and hair have shown that molten material is not far from the surface.

The composition of gases being emitted from the new vent also shows the presence of halogens-in particular, hydrogen chloride (HCl) and hydrogen fluoride (HF). These two gases are very soluble in basaltic magma and tend to stay dissolved until the melt approaches the surface. The halogen emission rate from Kilauea, including the new vent, is low compared to other erupting volcanoes around the world-for example, Kilauea's HF emission rate is less than one one-hundredth the HF emission rate of Masaya or Mount Etna. The appearance of HCl and HF, however, further reinforces the conclusion that shallow magmatic processes are occurring.

So, eruptively speaking, it seems clear enough that magma rose within the summit storage complex above the level it had held since 1982, the year of Kilauea's last summit eruption. The magma's upward migration caused the measured increase of tremor and gas release. What is less apparent is why this magma movement is occurring after over 25 years of quiescence and why it happened during a time when Kilauea was steadily deflating. We usually associate upward movement of magma with inflation (swelling) near the eruptive site.

One working hypothesis is that an inferred increase in magma supply to the volcano that occurred between 2003 and 2006 disrupted the previously steady flow of material into and out of, the summit storage complex. This factor of 2-3 supply rate pulse might have strained the summit and rift system, resulting in emplacement of an upper east rift dike and causing the small eruption on the flank of Kane Nui o Hamo shield in June 2007.

Further release of built-up magmatic system stresses is suggested from the ensuing eruptive sites downrift of Pu`u `O`o, the developed lava channel, and the TEB and associated shields that are now producing a stable and strong ocean entry.

The current summit activity, including formation of the new vent and a near doubling of total SO2 emissions from Kilauea, therefore, might be Pele's latest expression of pressure-driven stress-relief. As we wait for further answers to emerge, we volcano watchers can ponder the processes while we simultaneously engage the stress relief provided by Halema`uma`u's stunning roof-top view.

Activity update

Kilauea Volcano continued to be active at two locations: a vent in Halema`uma`u Crater is erupting elevated amounts of sulfur dioxide gas and very small amounts of ash. The resulting high concentrations of sulfur dioxide in downwind air have closed the south part of Kilauea caldera and produced occasional air quality alerts in more distant areas, such as Pahala, during trade wind cycles and communities adjacent to Hawai`i Volcanoes National Park during kona wind periods. Pu`u `O`o continued 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.

A new gas vent, about 6 m (yards) in width, was observed this past week inside Pu`u `O`o. The vent is perched on the east wall, approximately 20 m below the rim, and has been producing a hot, jetting plume. Lava from the 2007 Thanksgiving Eve Breakout (TEB) flow, erupting from fissure D of the July 21 eruption, continues to flow through what remains of the Royal Gardens subdivision and across the coastal plain to the ocean within well-established lava tubes. Over the past week, the Waikupanaha ocean entry has remained active, with small explosions and a vigorous plume on the east end of the new delta.

The public should be aware that lava deltas could collapse at any time, potentially generating large explosions in the process. 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 that are suddenly generated during delta collapse; these beaches should be avoided. In addition, the steam plumes rising from the ocean entries are highly acidic and laced with glass particles. Check the County of Hawaii Civil Defense Web site (http://www.lavainfo.us) or call 961-8903 for information on public access to the coastal plain and ocean entry.

Mauna Loa is not erupting. Six earthquakes were located beneath the summit. Continuing extension between locations spanning the summit indicates slow inflation of the volcano.

Three earthquakes beneath Hawai`i Island were reported felt within the past week; all of them occurred on Thursday, May 22, 2008. A magnitude-3.7 earthquake occurred at 8:44 a.m., H.s.t., and was located 7 km (4 miles) southeast of Kilauea summit at a depth of 2 km (1 mile). A magnitude-1.8 earthquake occurred at 5:22 p.m. and was located 2 km (1 mile) northeast of Hakalau at a depth of 10 km (6 miles). A magnitude-3.6 earthquake occurred at 10:26 p.m. and was located 7 km (4 miles) southeast of Volcano Village at a depth of 2 km (1 mile).

Visit our Web site (http://hvo.wr.usgs.gov) for daily Kilauea eruption updates and nearly real-time Hawai`i earthquake information. Kilauea daily update summaries are also available by phone at (808) 967-8862. Questions can be emailed to askHVO@usgs.gov. skip past bottom navigational bar


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Updated: June 12, 2008 (pnf)