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VOLCANIC FEATURES MAP to read text click red squares below 10 of 13 To view enlarged sample map, click in Red Outline. pp. 40-41 VOLCANIC FEATURES MAP (to return to top of page click blue squares) VN = VOLCANIC NECK (A monolith of volcanic rock jutting up from the surrounding landscape. This plug of hard lava once sat in the throat of a volcano—see page 52.) VF = VOLCANIC FIELD (clusters of many small volcanoes, which may include cinder cones, craters, fissures, lava flows and domes) active within the past 5 million years NP = NATIONAL PARK NM = NATIONAL MONUMENT SP = STATE PARK NRA = NATIONAL RECREATION AREA Volcanoes Not Expected to Re-awaken Potentially Hazardous Volcanic Centers Rio Grande Rift Valley The mid-section of our continent is literally being torn apart by forces deep within the Earth, an event that began about 30 million years ago and continues today. It's happening along a valley bounded by fractures in the Earth's crust—the Rio Grande Rift. Within this zone, molten rock (lava) periodically rises and spreads across the surface. And in the not-too-distant future, geologically speaking—several million years or so—New Mexico may be divided by an inland seaway. THE SOUTHWEST'S MOST DANGEROUS VOLCANO Within a 48-hour period in November 1997, more than a thousand earthquakes shook southern California's Long Valley. Earthquake swarms have been a daily occurrence there for the past 20 years, though most are small tremors that go unnoticed by residents. A magma-fed bulge within this ancient 10-by-20-mile crater has risen 31 inches (79 cm) since 1979; and, since 1994, carbon dioxide leaking from cracks in the mountain has killed acres of trees. The cataclysmic, explosive eruption that created this volcanic field about 760,000 years ago is believed to have been a thousand times greater than that of Mount St. Helens. Residents and visitors alike should be aware that Long Valley—with California's largest ski area—has high potential for another volcanic eruption. Scientists with the USGS Volcano Hazards Program feel certain it will blow but can't predict when. They remain nervous and monitor geologic unrest in the area daily. For updates, see http://quake.wr.usgs.gov/VOLCANOES/Long_Valley     Next Page     Sample Pages     Previous Page     Copyright © 2003 Wild Horizons Publishing, Inc. COPYRIGHT NOTICE