Unique volcanic activity seen in New Zealand

Geologists have witnessed a unique volcanic mudflow in Crater Lake, New Zealand, which could lead to the development of a new hazards assessment tool.

Volcanologist Sarah Fagents from the School of Ocean and Earth Science and Technology (SOEST) at the University of Hawaii had an opportunity to study volcanic hazards when mudflow broke through the banks of a volcanic lake at Mount Ruapehu in New Zealand.

Fagents and colleagues were there on a National Science Foundation (NSF)-funded project to study the long-forecast Crater Lake break-out lahar at Mount Ruapehu.

A lahar is a type of mudflow composed of water and other sediment that flows down from a volcano, typically along a river valley.

Lahars are caused by the rapid melting of snow and/or glaciers during a volcanic eruption, or as in the case of Mount Ruapehu, the breakout of a volcanic lake.

"Lahars can be extremely hazardous, especially in populated areas, because of their great speed and mass," said William Leeman, NSF program director for petrology and geochemistry.

"They can flow for many tens of miles, causing catastrophic destruction along their path.

"The 1980 eruptions at Mount St. Helens [in Washington], for example, resulted in spectacular lahar flows that choked virtually all drainages on the volcano, and impacted major rivers as far away as Portland, Oregon."

Warning system hailed a success

Fagents visited stretches of the lahar pathway before the breakout to assess pre-event channel conditions.

Although the event was predicted to occur in 2007, the recent decreased filling rate of Crater Lake suggested that the lake bank actually would not be overtopped until 2008.

However, several days of intense rainfall and increased seepage through the bank ultimately caused it to collapse much sooner, on 18 March 2007.

A lahar warning system had been installed at Mount Ruapehu, and was hailed a success after it successfully alerted officials to the onset of the lahar.

About 1.3 million cubic meters of water were released from Crater Lake, in total.

"We found a broad area covered in a veneer of mud and boulders," said Fagents.

"It was an unprecedented opportunity to see the immediate aftermath of such an event. It's particularly motivating for the students who were there to learn first-hand about lahar processes in such a dynamic environment."

Prediction of the effects of the events is of critical importance in populated volcanic regions.

Fagents is developing a computer model to simulate lahar emplacement and to predict the associated hazards.

"The intent is to adapt this model to account for different lahar triggering mechanisms, and for different locations, to make it widely applicable," said Fagents.

"The ultimate goal is provide a useful hazards assessment tool for future lahars."

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