Categorized | Featured, Sci-Tech, Volcano

Volcano Watch: New scientific results mark 5th anniversary of eruption of ChaiténVolcano, Chile

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

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.
This false-color image obtained from NASA’s Terra satellite on January 19, 2009, shows an ash plume (white plume spreading north, top) erupting from Chaitén Volcano. Red color indicates green vegetation. The brown color east and southeast of the volcano (lower left) shows extensive forest damage (400 square km; 155 square miles) from the early explosive eruptions, caused by ash fall and possibly by chlorine released from the magma. Scientists have concluded that magma fueling Chaiten’s eruptions ultimately originates beneath Michinmahuida Volcano, 17 km (10 miles) east of Chaitén. The town of Chaitén was evacuated a few days after the eruption began on May 2, 2008, before lahars and floods inundated most of the town.

This false-color image obtained from NASA’s Terra satellite on January 19, 2009, shows an ash plume (white plume spreading north, top) erupting from Chaitén Volcano. Red color indicates green vegetation. The brown color east and southeast of the volcano (lower left) shows extensive forest damage (400 square km; 155 square miles) from the early explosive eruptions, caused by ash fall and possibly by chlorine released from the magma. Scientists have concluded that magma fueling Chaiten’s eruptions ultimately originates beneath Michinmahuida Volcano, 17 km (10 miles) east of Chaitén. The town of Chaitén was evacuated a few days after the eruption began on May 2, 2008, before lahars and floods inundated most of the town.

One such noteworthy eruption began five years ago on May 2, 2008, at Chaitén Volcano in southern Chile. At the time, Chaitén was not perceived to be an active or hazardous volcano, and 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 15-20 km (9-12 miles) high in the air 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 Chaitén River where about 4,600 people lived.

After nearly 2 weeks of explosive activity, the eruption entered a prolonged (~18-20 months) phase of effusive lava-dome growth.

Despite a lack of monitoring, the Government of Chile and scientists responded quickly when the eruption began. Within 5 days, the small port town of Chaitén—located 10 km (6 miles) south of the volcano on the banks of the Chaitén 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 Chaitén River valley. Ash swept into the river raised the river bed by as much as 5 m (16 ft.) 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 (VDAP), a collaborative project between the U.S. Geological Survey and U.S. Agency for International Development (USAID), 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% SiO2)—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 (see the open access journal, www.andeangeology.cl) commemorating the 5th anniversary will report on several important aspects of the eruption and Chaitén’s eruptive history. A few highlights from previously published results and this issue include the following:

Chaitén was far more active in the past 10,000 years than was previously thought, including 3 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 5 to 10 km (3 to 6 miles) below the surface. Ascending at a rate of about 0.5 meters per second (1.6 feet per second)—an extremely high transport rate for rhyolite magma—the magma only took about 4 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 Chaitén was an inclined reservoir system that originated about 20 km (12.5 miles) beneath Michinmahuida Volcano, located 17 km (10 miles) east of Chaitén.

Estimates of lava effusion rates for the first few months of Chaitén’s dome growth, 45–66 cubic meters (59-86 cubic yards) per second, “are among the highest for historical lava-dome-forming eruptions.” For comparison, Kilauea’s long-term effusion rate for the Pu`u`O`o eruption is 5-6 cubic meters (6-8 cubic yards) per second.

This eruption is having a lasting impact on the Government of Chile. 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 in order to provide eruption forecasts and early warnings that were not possible when Chaitén erupted unexpectedly five years ago.

Caption: This false-color image obtained from NASA’s Terra satellite on January 19, 2009, shows an ash plume (white plume spreading north, top) erupting from Chaitén Volcano. Red color indicates green vegetation. The brown color east and southeast of the volcano (lower left) shows extensive forest damage (400 square km; 155 square miles) from the early explosive eruptions, caused by ash fall and possibly by chlorine released from the magma. Scientists have concluded that magma fueling Chaiten’s eruptions ultimately originates beneath Michinmahuida Volcano, 17 km (10 miles) east of Chaitén. The town of Chaitén was evacuated a few days after the eruption began on May 2, 2008, before lahars and floods inundated most of the town.

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