Word: semimolten
(lookup in dictionary)
(lookup stats)
Dates: all
Sort By: most recent first
(reverse)
Earthquakes, scientists now know, occur along the San Andreas because the immense slabs of rock that make up the earth's crust are ever so slowly sliding past one another, borne by poorly understood currents that roil through a sea of semimolten rock. By keeping tabs on the position of key landmarks on either side of the fault, scientists can measure the speed at which the plates are traveling, in this case about 2 in. a year. The problem for the Bay Area boils down to this: except for one short section, the plates on either side...
...1800s. It is hardly an obvious location. The theory of plate tectonics says quakes should happen most often along the edges of crustal plates, pancakes of rock a few score miles thick and thousands of miles across, which carry the continents on their backs as they slide across the semimolten mantle below. The plates ride over each other or grind together, and the earth shakes. But New Madrid is right in the middle of a plate, a place where earthquakes are generally not seen...
...seismographs and tiltmeters - which measure the swelling of the earth's surface - scientists have determined that the eruption was triggered by a magnitude5 earthquake that shook the mountain on May 18, the day of the volcano. The tremor dislodged a flank of the mountain already swollen from rising semimolten rock. A huge hunk of the mountain rumbled downhill like a great sliding door, uncovering rock saturated with compressed gases. Exposed to the air, the gases exploded. Geologists are encouraged by the fact that the lava dome that has been forming in Mount St. Helens' crater now appears...
...cause of the changes can be traced, at least in part, to plate tectonics, the movement of the great crustal plates that ride on the earth's semimolten mantle and provide its solid outer shell. Some 45 million to 50 million years ago, the plate that carries the Indian subcontinent was pushing up into the underbelly of Asia, slowly thrusting up the massive mountain range now called the Himalayas. This new barrier to global wind circulation helped change weather patterns, altering average temperatures around the world. By about 14 million years ago, climates that had been tropical had turned largely...
Mount Usu had last erupted in 1945. Since then, magma, or semimolten rock from the mantle surrounding the earth's core, had been slowly and quietly rising through cracks under the peak of the mountain, building up tremendous pressures and triggering repeated earth tremors that rocked Hokkaido. Finally, on Aug. 7, the 725-meter (2,400-ft.) Usu awakened with a roar like that of a bomb. A huge black cloud soared to a height of 12,000 meters (39,000 ft.). A dense shower of gray ash and chunks of porous, rock-like pumice poured...