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Volcanowatch

June 12, 2008

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


The Puzzling Plume

Geologist collecting ash at the Halema`uma`u overlook fence.  The collector is attached to the fence three feet above the ground to reduce sample contamination from windblown material.
Geologist collecting ash at the Halema`uma`u overlook fence. The collector is attached to the fence three feet above the ground to reduce sample contamination from windblown material.
The new Halema`uma`u Overlook vent is now only three months old, and the accompanying plume is relatively small in terms of previous explosive eruptions of Kilauea, but it has been front page news to Hawai`i's citizens and visitors. While watching the voluminous white plume rising thousands of feet into the air by day or admiring the strong glow at night, you're probably wondering what exactly is streaming out of the new vent besides gas. The short answer is ash-rock dust and bits of volcanic glass less than 2 mm (0.08 inches) in diameter. But how do we catch the ash coming out of the plume, and what are we doing with it?

Basically, we let it fall into our scientific laps. Each morning around daybreak, rain or shine, an HVO scientist goes to the Halema`uma`u overlook to collect the ash that has fallen from the plume since the previous morning. After experimenting with different types of ash collectors, 12-quart plastic buckets, weighed down with rocks, emerged as the best.

The contents of the ash collectors are brought back to HVO and weighed, and the average accumulation rate is calculated. The ash is then inspected under the microscope to note variations in its make-up. We're especially interested in the amount of juvenile material (fresh lava) versus the amount of lithic material (bits of older rock or debris from the conduit walls) in each day's collection.

The juvenile material, which comes from lava beneath the crater floor, is sent to our sister volcano observatory near Mount St. Helens for analysis. The results indicate that the chemical composition of the lava at the summit is almost identical to the lava currently erupting from the east rift zone and flowing into the ocean.

Because the ash that is already on the ground can also be blown into our collectors by strong winds, we had to devise ways to minimize collection of the windblown debris while maximizing the collection of ash falling from the plume. An ash collector was placed on the Halema`uma`u overlook fence, elevated about 1 m (3 feet) off the ground. Elevating this collector has proven enough to do the job.

The entire array of collectors are laid out within a few hundred meters (yards) of the vent, positioned to accumulate ash in both trade- and kona-wind conditions.

But that's not all that has been ejected from the new vent. Debris from the three explosions (on March 19, April 9, and April 16), including blocks of older lava as large as 3 feet in diameter and fresh spatter, litters the area around the overlook. Because of this pervasive debris, it would be difficult to tell whether new blocks are ejected from the vent. The solution was to clear a 2.2-m (7-foot) square area of all rock debris larger than 2-3 inches. This "explosion trap" should allow us to identify new material if it is ejected from the vent in this area. None has been seen since April 16.

So, what does all of this dirty, smelly work under the plume tell us? Since juvenile material first appeared in the ash on March 23, it has consistently been seen in the samples. Juvenile material is something geologists look for in volcanic ash, because it tells us that fresh lava is close to the surface. But the appearance of juvenile material, combined with the nature of our visual and thermal observations, still cannot tell us exactly how deep below the floor of Halema`uma`u Crater the lava resides. As we continue to collect the ash each day, we watch and listen for the possibility of seeing fresh lava in the crater again.

Activity update

Kilauea 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 Kilauea caldera and produced occasional air quality alerts in more distant areas, such as Pahala and communities adjacent to Hawaii Volcanoes National Park during kona wind periods.

Pu`u `O`o 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.

The new gas vent observed on May 23 inside Pu`u `O`o has remained active, with no observed change. 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 Royal Gardens and across the coastal plain to the ocean in well-established lava tubes. Over the past week, the Waikupanaha ocean entry has remained active, with occasional small explosions and a variable plume.

Be aware that lava deltas could collapse at any time, potentially generating large explosions. 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. Continuing extension between locations spanning the summit indicates slow inflation of the volcano.

One earthquake beneath Hawai`i Island was reported felt within the past week. A magnitude-3.1 earthquake occurred at 9:26 p.m., H.s.t., on Monday, June 09, 2008, and was located 6 km (4 miles) southwest of Pahala at a depth of 33 km (20 miles).

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 16, 2008 (pnf)