Word: magma
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Unlike earthquakes, which often happen without warning, impending volcanic eruptions generally signal their arrival. Before a blowup, instruments can detect a series of tremors in the mountain, which indicate that molten rock, called magma, is coming up from deep inside the earth. The magma rises gradually, opening fissures that serve as its pipelines to the surface. What happens next depends on the composition of the magma. If it is fairly liquid, it generally produces a stately lava flow that poses more of a threat to property than to humans. Hawaiian volcanoes tend to follow this pattern...
...zone where sections of the earth's crust, known as plates, are colliding. Generally the weaker oceanic plates are forced beneath the thicker continental slabs. The friction of grinding rock, combined with heat welling up from the earth's interior, transmutes the lower edge of the oceanic plate into magma. Thick with silica, this type of magma tends to solidify near the surface, forming domes and plugs that seal off the channels through which the magma rises. Such blockages turn a volcano into a giant pressure cooker. At a certain point, when the surrounding rock is no longer strong enough...
...main tools of the volcanologist include seismometers, which record the swarms of tiny earthquakes that occur as the magma rises. Chemical sensors, mounted on airplanes, can detect increases in sulfur-dioxide emissions, indicating that magma has reached the surface. In addition, the physical swelling of mountain slopes, well documented at Mount St. Helens, is a sign of explosive potential. Laser-based devices can pick up minute bulges that are about the width of a nickel and still invisible to the naked eye. In Japan researchers have set up video cameras to monitor the shape and color of fumes...
...seven years since Mount St. Helens exploded in a spume of gas, ash and pumice, there have been 24 additional eruptions at the volatile peak in the Cascade Range. The last, a small explosive belch of magma that added 85 ft. to the height of the lava dome inside the crater, occurred eight months ago. As a result, the U.S. Forest Service, cautious guardian of the 110,000-acre Mount St. Helens National Volcanic Monument, has decided to let the general public have a closer look at a postvolcanic environment. Since early May, some 100 climbers a day have been...
...rise of magma is often accompanied by swarms of small local earthquakes. Such tremors, which enable scientists to estimate how close to the surface the magma may be, have been felt at Mount Hood in neighboring Oregon and at Mount Shasta in Northern California as well as Mount St. Helens. In addition, the USGS study notes that since 1982 earthquakes have shaken California's Coso Range, a volcanic region west of Death Valley; Yellowstone National Park, which is famed for its hot springs and geysers, notably Old Faithful; and Mammoth Lakes, a popular California ski resort near the Nevada...