New scientific results mark 5th anniversary of eruption of Chaiten volcano, Chile


Some volcanic eruptions have a much higher overall impact on society than others. The impact depends on various factors, such as eruption size; the degree to which the activity affects people, economies and governments; the success or failure of emergency response to save lives and property; and the way in which follow-up scientific studies contribute to the advancement of volcano science and risk reduction elsewhere.

One noteworthy eruption began May 2, 2008, at Chaiten volcano in southern Chile. At the time, Chaiten was not perceived to be active or hazardous, so it was not monitored by scientists.

After only 24 hours of felt earthquake activity, a series of strong, explosive events sent multiple ash columns nine to 12 miles high for more than a week. Ash blanketed vast areas of Chile and Argentina with fine-grained ash deposits setting the stage for a destructive lahar, mudflow, and flood at the mouth of the Chaiten River where about 4,600 people lived.

After nearly two weeks of explosive activity, the eruption entered a prolonged – 18 to 20 months – phase of effusive lava dome growth.

Despite a lack of monitoring, the government of Chile and scientists responded quickly after the eruption began. Within five days, the small port town of Chaiten, six miles south of the volcano on the banks of the Chaiten River, was completely evacuated.

Less than a week later, flood sediment buried much of the town following a modest rainfall that swiftly eroded a large volume of ash deposited on steep hill slopes above the Chaiten River valley. Ash swept into the river raised the river bed by as much as 16 feet within 24 hours of the onset of rainfall.

Chilean scientists quickly installed a volcano monitoring network consisting of several seismometers to track the volcano’s activity. Their work was supported in part by scientists from the U.S. Volcano Disaster Assistance Program, a collaborative project between the U.S. Geological Survey and U.S. Agency for International Development, Office of U.S. Foreign Disaster Assistance.

This eruption was of particular concern and interest to scientists because the type of magma erupted, high-silica rhyolite – about 75 percent silicon dioxide — has fueled some of Earth’s largest explosive eruptions. There are few direct observations of such eruptions and their impacts, and none monitored with modern scientific capabilities and networks.

A forthcoming issue of the journal Andean Geology – andeangeology.cl – commemorating the fifth anniversary will report on several important aspects of the eruption and Chaiten’s eruptive history. A few highlights from previously published results and this issue include the following:

Chaiten was far more active in the past 10,000 years than was previously thought, including three substantial eruptions in the past 5,000 years and an eruption in the 17th century that produced “impacts and deposits similar to those of the 2008-2009 eruption.”

The initial eruption was fed directly by magma that originated at least three to six miles below the surface. Ascending at a rate of about 1.6 feet per second — an extremely high transport rate for rhyolite magma — the magma took only about four hours to reach the surface.

Comparison of satellite images before and after the eruption revealed ground deformation that led scientists to conclude that the source of magma erupted by Chaiten was an inclined reservoir system that originated about 12.5 miles beneath Michinmahuida volcano, 10 miles east of Chaiten.

Estimates of lava effusion rates for the first few months of Chaiten’s dome growth – 59 to 86 cubic yards per second – “are among the highest for historical lava dome-forming eruptions.” For comparison, Kilauea’s long-term effusion rate for the Puu Oo eruption is six to eight cubic yards per second.

This eruption is having a lasting impact on the Chilean government. With more than 120 potentially active volcanoes, the government is supporting an expanded national volcano hazard monitoring and hazard assessment program. Today, scientists continue to build the real-time monitoring networks at Chile’s highest-risk volcanoes to provide eruption forecasts and early warnings that were not possible when Chaiten erupted unexpectedly five years ago.

Kilauea activity update

A lava lake within the Halemaumau Overlook vent produced a nighttime glow visible from the Jaggar Museum overlook and via HVO’s webcam during the past week. The lake level rose over the past week and was about 165 feet below the floor of Halemaumau Thursday.

On Kilauea’s east rift zone, breakouts from the Peace Day tube remain active on the pali and on the coastal plain. Small ocean entries are active on both sides of the Hawaii Volcanoes National Park boundary. A new breakout from a spatter cone on the northeast edge of Puu Oo’s crater floor started on May 6 and has traveled a short distance north, following the path of the inactive Kahaualea flow from last month.

One earthquake was reported felt in the past week across Hawaii Island. At 3:12 p.m. May 6, a magnitude-3.4 earthquake occurred three miles southeast of Puu Oo at a depth of five miles.

Visit hvo.wr.usgs.gov for Volcano Awareness Month details and Kilauea, Mauna Loa and Hualalai activity updates, recent volcano photos, recent earthquakes and more; call 967-8862 for a Kilauea summary; email questions to askHVO@usgs.gov.

Volcano Watch is a weekly article and activity update written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.