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Mapping the Earth's Largest Volcanoes
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# : |
19863 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
5 / 1991 |
2,729 Words |
| Author
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Grant Heiken
Grant Heiken is a research scientist in the geology and
geochemistry group of the Los Alamos National Laboratory in
Los Alamos, New Mexico. |
Volcanoes of all types cover the earth's surface, both above and below sea level. They range in size from the few cubic meters of volcanic ash erupted at a geothermal well in Iceland to giants many kilometers thick and tens of kilometers wide. Volcanic activity is a constant reminder that the earth is a dynamic planet and is continually changing its appearance. Eruptions have occurred throughout the history of our planet and will continue to do so for billions of years.
The earth is unique in having abundant water--in the atmosphere, on the surface as streams, lakes, and oceans, and as groundwater to depths of many kilometers. A volcano's complex plumbing system, consisting of the intrusions of molten rock that underlie it, heats up the groundwater, which moves through pores and fractures as heated water or steam, attacking and sometimes dissolving minerals within the rocks. If these hot fluids reach the surface, they may form hot springs, steam vents, geysers, or even acres of barren, acid-altered ground. Thermal areas, such as Yellowstone Park and those on the North Island of New Zealand, supply only surficial clues to the vast geothermal resources that underlie these young volcanic fields.
If man is to harness the potent heat energy in these natural resources, he must probe the third dimension, the depth below the ground surface within complex volcanic/geothermal systems. Despite the development of a multitude of sensing technologies, the most effective method for mapping these complex underground structures and monitoring their equally complex processes is by drilling into the volcano and its plumbing system.
Scientific drilling into volcanoes has gone on for many years in the oceans. The ocean drilling program has revolutionized the earth sciences by providing basic data that support, for example, the theory of plate tectonics, and that greatly expand knowledge about how volcanoes erupt underwater. In contrast, scientific drilling on the continents is in its infancy and has just begun to reveal a third dimension to landlocked earth scientists. Continental drilling has been initiated by drilling into the largest volcanoes, which also contain extensive geothermal reservoirs.
The largest volcanoes
The largest of earth's volcanoes have deposited tens to hundreds of cubic kilometers (a few to a few hundred cubic miles) of volcanic ash during single eruptions lasting a few days or weeks. Such gargantuan eruptions drain off huge
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