Are volcanoes fed by highly viscous magma more likely or less likely to be a greater threat to life and property than volcanoes supplied with very fluid magma?
What will be an ideal response?
When fluid basaltic magmas erupt, the pressurized gases readily escape. Occasionally, these expanding gases propel incandescent lava hundreds of meters into the air, producing lava fountains. Although spectacular, these fountains are usually harmless and generally not associated with major explosive events that cause great loss of life and property. At the other extreme, highly viscous magmas expel particles of fragmented lava and gases at nearly supersonic speeds that evolve into buoyant plumes called eruption columns. Because silica-rich magmas are sticky, a significant portion of the gaseous materials remain dissolved until the magma nears Earth's surface, at which time tiny bubbles begin to form and grow. When the pressure of the expanding magma body exceeds the strength of the overlying rock, fracturing occurs. As magma moves up the fractures, a further drop in confining pressure causes more gas bubbles to form and grow. This chain reaction may generate an explosive event in which magma is literally blown into fragments that are carried to great heights by the hot gases. These violent eruptions can cause great loss of life and property.
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Subtropical steppe
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Which one of the following ecosystem services has been enhanced most by humans?
A) Capture fisheries B) Pollination C) Crops D) Wood fuel
In 2008, Russian troops entered the __________ region to support its move towards independence from __________.
a. South Ossetian ; Georgia b. Abkhazia; Transcaucasia c. South Ossetian; Chechya d. Adjara; Georgia e. South Ossetian ; Transcaucasia
The toxicity of industrial pollutants may go unrecognized for all of the following reasons except
A. their harmful effects may be slow to develop. B. they often cause skin and eye irritation. C. they may be harmful only in some concentrations or circumstances. D. they cannot be tested for safety on all organisms.