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Tale of two magmas may be to blame for explosive volcanic eruptions

Ben Anderson
Summit of Augustine viewed from the south.
Image courtesy of AVO/USGS
Pavlof volcano and eruption plume on evening of Aug. 30, 2007. View is to the south. Plume height approximately 17-18,000 ft.
Chris Waythomas/Alaska Volcano Observatory photo
The "Snowy Hole," a fumarole on the south side of Snowy Volcano, located in the Katmai region of the Alaska Peninsula.
Cyrus Read/Alaska Volcano Observatory photo
Aerial image of Akutan Volcano. (August 5, 2011)
Burke Mees/Alaska Volcano Observatory photo
A photo of Iliamna volcano on the lower west side of Cook Inlet.
Photo courtesy AVO/USGS
Aerial view looking southwest of a portion of the 4-6 km ice-filled summit caldera of Mount Wrangell, a 14,163-foot andesite shield volcano in 1987. It is the only volcano in the Wrangell volcanic field to have had documented historical activity consisting of several minor, possibly phreatic eruptions in the early 1900's.
R. Motyka/ADGGS photo
Mount Novarupta
USGS photo
Aerial view, looking east, of Aniakchak caldera, one of the most spectacular volcanoes on the Alaska Peninsula. Formed during a catastrophic ash-flow producing eruption about 3,400 years ago, Aniakchak caldera is about 10 km (6 mi) across and averages 500 m (1,640 ft) in depth. Voluminous postcaldera eruptive activity has produced a wide variety of volcanic landforms and deposits within the caldera. The volcano is located in Aniakchak National Monument and Preserve, Alaska, which is administered by the National Park Service.
AVO photo
From the USGS caption: Mount Cleveland forms the western half of Chuginadak Island in the central Aleutian Islands. This symmetrical, 1,730-m (5,676 ft)-high stratovolcano and has been the site of numerous eruptions in the last two centuries; the most recent eruption occurred in 1994. In 1944, a U.S. Army serviceman was reportedly killed by an eruption from Mount Cleveland.
Alaska Volcano Observatory photo
Eruption of Great Sitkin Volcano, 1974.
Steve Kelly photo; courtesy Paul W. Roberts
Aerial view of the eruption column from Mount Spurr volcano on Aug. 18, 1992. A light-tan cloud ascending from pyroclastic flows is visible at right. The 11,070 footh summit lava dome complex of Mount Spurr is visible at left.
R. McGimsey/U.S. Geological Survey photo
Mt. Redoubt's active lava dome on May 8, 2009
AVO photo

The last time the Las Cañadas volcano erupted was more than 150,000 years ago, but scientists from the University of Southampton in the United Kingdom studying the volcano's explosive past say they have determined what causes massive eruptions like the prehistoric blast.

The Las Cañadas volcano has seen at least seven major eruptions in the last 700,000 years, and according to a new study published in Scientific Reports, they may now have found the root of the devastating blasts. The history of the caldera -- located on the island of Tenerife in the Canary Islands -- is well documented, but the new research is the first to nail down a possible cause of such eruptions.

"Despite considerable scientific interest in the volcano and associated hazards including major landslides, little is known about the triggers for these large-scale events," the study's authors write.

Knowing what caused the eruptions could be key to developing an advance warning system before the volcano erupts again, which would prove devastating to the island populated today by more than 900,000 people.

According to researchers, the eruptions were caused when younger, hotter magma mixed with cooler, older magma within the volcano, causing a buildup of pressure that resulted in ash and debris columns reaching 15 miles into the air.

"By comparison, even the smallest of these eruptions expelled over 25 times more material than the 2010 eruption of Eyjafjallajökull, Iceland," a report from the University of Southampton said. That eruption disrupted European air travel for nearly a week as ash caused hazards to aircraft.

Researchers determined the Las Cañadas trigger by examining igneous rocks formed during the previous eruptions, when "crystal mush" lining the walls of the underground magma chamber mixed with magma left over from the blast. Those rocks indicated the blending of the two types of magma and the resulting explosion.

Another serious eruption from the volcano in the Canary Islands, off the northwest coast of Africa, has the potential for major impacts across that continent and Europe, so knowing what causes the eruptions could be key to an advance warning system.

“Our findings will prove invaluable in future hazard and risk assessment on Tenerife and elsewhere," said Dr. Tom Gernon, one of the authors of the study. "The scale of the eruptions we describe has the potential to cause devastation on the heavily populated island of Tenerife and major economic repercussions for the wider European community."

Whether the same combination of old and new magma could be responsible for similar eruptive events in the last hundreds of thousands of years isn't clear, but the new study represents a good jumping-off point for further research.

You can read the full study here.

Contact Ben Anderson at ben(at)alaskadispatch.com