Explosive Volcanism Inception, Evolution, and Hazards (1984) / Chapter Skim
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OVERVIEW AND RECOMMENDATIONS
OVERVIEW AND RECOMMENDATIONS
Pages 3-12
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From page 3... ...
states that "neither the probability nor the nature, scale, or timing of a possible eruption can be determined as yet." Field studies in the Long Valley area suggest that such an eruption might take a variety of forms but would most likely include explosions of groundwater superheated by contact with magma, ash falls, and minor pyroclastic flows, terminating with the extrusion of a rhyolite dome. More harrowing is the possibility of eruption of a major pyroclastic flow of the magnitude of the Bishop Tuff, erupted from Long Valley 700,000 years ago.
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From page 4... ...
In contrast, volcanic loci form a complex network of rectilinear zones in the Basin and Range, where extensional tectonics prevail (see Chapter 4)
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The nature of magmatic movements will in turn control the opportunities for chemical interaction between melts and rocks forming conduit walls and the possible development of secondary, more silicic melts. Some alkali basalts contain abundant inclusions of mantle rocks, indicating rapid transport from mantle sources with little opportunity for interaction with wall rocks.
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From page 6... ...
Problems that are important from the viewpoints of both scientific progress and hazard evaluation include the interrelationships of physical factors that determine the explosive character of an eruption and the identification of sources of volatiles involved in explosive eruptions. The variety of sizes and shapes of volcanic jets associated with violent eruptions reflects differences in the geometric shapes of near-surface parts of the volcanic systems and, secondarily, the differences in thermodynamic properties and rheology of the erupting fluids.
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From page 7... ...
Helens, possibly including loci outside the Cascades, may become active in the next few decades. The youngest volcano in the conterminous United States outside of the Cascade Mountains is an alkali basalt cinder cone and associated flow that erupted only 390 yr ago in the eastern Mohave Desert, 180 km from Los Angeles (see Chapter 1)
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From page 8... ...
The diversity and extent of these interactions, however, is poorly understood. In western North America there is a broad correlation of magma composition with tectonism in that andesites are primarily erupted in zones of tectonic compression, whereas eruption of basalt, sometimes accompanied by rhyolite, is characteristic of broad areas under tectonic extension.
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From page 9... ...
We urge the Department of Defense to develop policies wherein maximum use, including volcanological use, is made of data acquired during routine geophysical monitoring.
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From page 10... ...
Efforts to provide such a groundwork are under way at Mammoth Lakes. The USGS should continue and extend these communication efforts with local, state, and federal agencies wherever signs develop of potential volcanic activity that could be a danger to the public.
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