March 1, 2004

Satellite tots up volcanic heat

Eruptions dwarfed by man-made energy output.

by Mark Peplow
Nature News

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Volcanoes throw out only a tiny fraction of energy compared with that produced by mankind, say scientists who have used satellite measurements to do a survey of the Earth's heat output.

In 2001, the amount of heat energy produced by volcanoes was 1000 times less than the energy consumed by the United States, the researchers report in the current issue of Geology1. They assume that most of the man-made energy, which is used for everything from residential lighting and heating to manufacture and transport, will end up in the form of heat.

Robert Wright and Luke Flynn from the University of Hawaii in Honolulu used the NASA satellite MODIS (Moderate Resolution Imaging Spectroradiometer) to measure the heat emitted by the world's 45 most active volcanoes, which are responsible for the majority of the Earth's volcanic heat.

Over 2001 and 2002, these volcanoes kicked out about 5 x 1016 joules per year - enough to power New York city for a few months.

The data bring us closer to a global survey of volcanic heat output. While the numbers are small in terms of the Earth's overall heat generation, they contribute to our understanding of the planet's heat flow. That in turn helps researchers work out the details of how the Earth's innards circulate, pushing and pulling the continents around the globe.

Better than ballpark

In the past, scientists used land-based temperature readings taken from the surface of volcanoes to work out how much heat was given off. "It gave you some pretty ballpark figures," says Bill McGuire from the Benfield Hazard Research Centre at University College London.

Satellites are more accurate, and are potentially useful for volcanic forecasting too, says McGuire. Wright and Flynn think that a 20-year inventory of heat flow should be enough to spot patterns in volcanic activity that could help predict eruptions. "Satellite monitoring is becoming vital to vulcanology," says McGuire.

The scientists also found that single eruptions of one or two volcanoes can make up a large part of the year's heat budget. Nyamuragira in the Democratic Republic of Congo and Mount Etna in Italy contributed about 40% of the volcanic energy total for 2001.

When Mount St Helens erupted in 18 May 1980, it released more than 1018 joules of heat at once - about 20 times the total heat flow from all the volcanoes studied in 2001.

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