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Volcanowatch

September 17, 2009

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


Mount St. Helens' eruption of 2004-2008 described in newly published USGS book

The crater of Mount St. Helens as seen on August 9, 2009. Note the narrow glaciers between the crater walls and the now inactive lava spines and domes in the crater center.
The crater of Mount St. Helens as seen on August 9, 2009. Note the narrow glaciers between the crater walls and the now inactive lava spines and domes in the crater center.

It is placid these late-summer days at Mount St. Helens, the mainland U.S. volcano that began in 2004, a sluggish, relentless eruption that lasted for 3-1/2 years. Since late January 2008, when the eruption ended, the only hullabaloo has been around a recently published book that describes the onset and first 18 months of that eruption.

The U.S. Geological Survey has recently published a collection of scientific and hazard-response findings about the first 18 months of this eruption in Professional Paper 1750, A Volcano Rekindled: The Renewed Eruption of Mount St. Helens, 2004-2006. This 37-chapter book includes articles written by current and past staff members of the Hawaiian Volcano Observatory.

The book is available free-of-charge online, where it may be downloaded as chapters, sections, or in its entirety (http://pubs.usgs.gov/pp/1750). A printed hardbound version is available for sale (USGS Information Services, Box 25286, Federal Center, Denver, CO 80225; telephone: 888 ASK-USGS).

The 2004 onset of volcanic unrest was exciting for residents and visitors in Washington State, mainly because of the public remembrance of the previous great eruption. Would the ferocity of the 1980 eruption be wreaked anew? Beginning in September 2004, several weeks of heightened seismicity—tens of thousands of earthquakes—culminated in small steam-fired explosions on October 1, 2004. None of these explosions, however, had even a thousandth of the bang that characterized the events of nearly 30 years ago.

Lava reached the surface a few days later, on October 11, 2004. Thereafter, relentless extrusion built a lava dome. Explosive activity was rare, and the dome's growth was imperceptible on a day-by-day basis. Consequently, people in the region grew unaware that the eruption persisted as long as it did.

Several lines of evidence support the view that no new magma was involved in the 2004-2008 eruption. Instead, the recent episode may be viewed as the straggling of the 1980s event.

For example, earthquakes were rarely deeper than 2-3 km, which is one line of evidence that the volcano was receiving little, if any, new magma in 2004. Emplacement of magma from greater depth would have left a trace of deeper earthquakes.

The GPS receiver near the volcano showed no inflation in the months preceding September 2004. Presumably the volcano was already pressurized, its magma having moved into a position favorable for eruption as early as the late 1980s or early 1990s.

The 2004-2008 magma lacked much of the volatile gas that characterized magma of the 1980s. It had grown as flat as the two-day-old Coke in the glass on the counter.

Finally, the lava that reached the surface was dacite similar to that of the 1980s. Virtually nothing in the analysis of crystals and glass required an explanation beyond the resurrection of magma already stored in the Earth's shallow crust.

While Mt. St. Helens may be far from Hawai'i, those of you in our volcano-savvy public who are interested can find in-depth discussions of these views and others, explained more fully by the scientists who contributed their data and interpretations, in Professional Paper 1750.

Kīlauea Activity Update

Lava continues to erupt from the TEB vent, on Kīlauea's east rift zone and flow through tubes to the ocean at Waikupanaha. A lava breakout from the tube near the top of the Royal Gardens subdivision has been active sporadically since early in the week. The flows are mostly staying close to the breakout point and are building a broad shield-shaped mound of lava.

Faint glow above the vent at Kīlauea's summit has been visible at night. Early this morning, a small explosive eruption ejected juvenile and lithic tephra onto the rim of Halema`uma`u above the vent. Volcanic gas emissions remain elevated, resulting in high concentrations of sulfur dioxide downwind.

No earthquakes beneath Hawai`i Island were reported felt this past week.

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.

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Updated: October 1, 2009 (pnf)