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Global Positioning System receiver at a benchmark along Fortification Bluff, overlooking Cook Inlet in Alaska; a band of cloud wreaths Augustine Volcano in the distance.

Volcano in 1989–90). During this century, volcanoes in California, Washington, Alaska, and Hawaii have devastated hundreds of square miles and caused major economic hardships and loss of life. Significant impacts can occur hundreds of miles from a volcano. For example, in the past 25 years, more than 40 aircraft have been damaged by encounters with volcanic ash clouds. A Boeing 747 flying through an ash cloud from Alaska's Redoubt Volcano in 1989 temporarily lost power in all four engines and did not regain power until only a few thousand feet above the ground.

The goals of the USGS Volcano Hazards Program are to reduce loss of life caused by volcanic activity and to minimize the social and economic disruption that can occur when volcanoes threaten to erupt. These goals are pursued by studying volcanic processes to better understand how volcanoes act and to better interpret warning signs; by studying selected volcanoes near population centers to assess the hazard posed by future activity at the volcano; and by monitoring restless volcanoes to interpret the likelihood and probable style of an eruption.

Living with Volcanoes

lthough volcanic activity worldwide is

not on the rise, the impact on people and their activities is increasing as more homes are built in the shadow of volcanoes and as more long-distance aircraft fly over remote volcanoes. Because no

violent eruptions threatened lives or property in the United States during the past year, USGS scientists were able to focus on expanding our basic knowledge of the causes and effects of the many types of volcanic activity. For example, in March 1993, the USGS organized a workshop of Japanese and USGS volcanologists who are studying volcano monitoring and processes of explosive eruptions. The workshop was held in Menlo Park, Calif., and was attended by more than 100 volcanologists, mainly from the United States and Japan but including scientists from several other countries. Workshop participants identified two topics as the most important for collaborative research to mitigate the hazards of explosive eruptions—processes of dome growth and seismic precursors to explosive eruptions. To minimize the hazard that volcanic ash poses to aircraft, the USGS is working actively with the aviation industry, aircraft manufacturers, and other governmental agencies to gain a better understanding of how ash plumes behave over time, how to detect ash plumes quickly in remote airspace, and how to communicate information in real time to aircraft in the air or about to depart along affected routes. During FY 1993, the USGS cosponsored or participated in three international workshops on ash and aviation safety. The proceedings of the most recent workshop, which concerned the impact of volcanic ash on airports, are summarized in USGS Open-File Report 93–518, “Volcanic Ash and Airports: Discussions and Recommendations from the Workshop on Impacts of Volcanic Ash on Airport Facilities." In addition, USGS scientists are working with the International Civil Aviation Organization in revising procedures for detecting and issuing warnings of ash plumes in foreign airspace. The USGS also has formal collaborative agreements with the Federal Aviation Administration, the National Weather Service, and other regional agencies involved with disaster mitigation to address issues of aviation safety and volcanic eruptions. Augustine Volcano, one of the most active in Cook Inlet, has been the focus of special study because of its frequent eruptions (1935, 1963–64, 1976, and 1986 in this century alone). USGS scientists have installed three tiltmeters and three Global Positioning System receivers

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on Augustine Island to monitor ground deformation continuously. If an eruption threatens, the Alaska Volcano Observatory—a consortium of the USGS, the University of Alaska, and the State of Alaska— should be able to warn people in the region, including the cities of Anchorage and Homer, and alert commercial aircraft to any possible danger. These warnings will help to minimize the socioeconomic disruption caused by volcanoes. In May 1991, the Philippine Government invited USGS scientists to collaborate with Filipino volcanologists in assessing unrest at previously little-known Mount Pinatubo. The team provided warnings that led to the timely evacuation of thousands of Filipino residents and U.S. military personnel and dependents and hundreds of millions of dollars worth of military equipment just before the climactic eruption in June 1991. Clark Air Base was closed prematurely as a direct result of this volcanic activity, and ongoing mudflows and secondary eruptions continue to endanger the area. Scientists from the USGS, the Philippines, and the U.S. Army Corps of Engineers are investigating these hazards, funded in part by the U.S. Department of State.

James Riehle is on the staff of the USGS Volcano Hazards program and the Geothermal Investigations program and has published extensively on volcano systems

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promotes multidisciplinary research to expand our knowledge of deep crustal environments and processes that control or influence near-surface geology. The program provides basic information on hazards; management of land, mineral, and energy resources; and environmental concerns about the disposal of wastes. The challenges of deep drilling spur improvements in drilling instruments and technology.

Evolution of Volcanic Arcs

B. interdisciplinary research on the evolution of volcanic arcs (belts of volcanoes that parallel the deep ocean trenches) has led to a new understanding of their behavior, especially the relationships among volcanic eruptions (often explosive), earthquakes, and the descent of cold oceanic crust into the Earth's mantle. This new conceptual understanding is based on experimental and theoretical studies funded by the Deep Continental Studies program over the past 2 years. The new model is based on the complex relationships among the dehydration of the descending ocean crust, the formation of a very dense rock called eclogite (which forms rapidly from crustal material under certain pressure and temperature conditions in the presence of water), and the melting of oceanic crust and overlying mantle rocks to form magmas. The formation of eclogite is controlled by the influx of water and the kinetics of mineral reactions that convert relatively voluminous minerals, commonly found in oceanic crust, into the much denser minerals that compose eclogite. The eclogite forms only along a narrow layer of the sinking slab, where the crustal minerals are present; the rest of the slab consists of mantle minerals that do not change volume as they sink. The reduction in volume that results from the formation of eclogite causes stresses in the oceanic crustal slab; these stresses, in turn, cause earthquakes. (An analogy is the cracking caused by thermal shock when an object is suddenly and unevenly heated or cooled, such as when a cold ice cube is dropped into lukewarm water.) Hence, water from the sinking oceanic crust not only aids in the melting of crust and mantle but also facilitates chemical

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reactions that are ultimately the cause of powerful earthquakes.

Because most of the Earth's volcanoes are in volcanic arcs and most earthquakes occur within narrow zones beneath volcanic arcs, our new model provides a framework for understanding arc mechanics. We can now begin to quantify the buildup of stresses in downgoing slabs and improve our understanding of the episodic character of earthquakes and volcanic eruptions. As our understanding of the model's numerical aspects improves, we will be able to test it. The Pacific Northwest, between Seattle and Portland where the Juan de Fuca plate is forced beneath the North American plate, would be an excellent test area. The results of this fundamental work will have significant impact on earthquake and volcano hazards mitigation all over the world, wherever subduction zones are found.

Steven Bohlen coordinates the USGS Deep Continental Studies program and has made numerous contributions to research on the mineralogy of the Earth's crust and mantle

Mineral-Resource Surveys

ineral-resource surveys provide the

mineral-resource and mineralenvironmental information required to make land-use and environmental policy decisions for effective management, preservation, and use of the Nation's lands and resources. The USGS is increasing its emphasis on environmental mineral investigations by developing and applying geochemical and geophysical techniques to regional and site-specific characterizations of the environment. For example, USGS geoscientists are helping to identify, characterize, and remediate environmental problems associated with active and abandoned mine sites. Selection and scheduling of study areas are conducted in close cooperation with Federal landmanaging agencies, the U.S. Bureau of Mines (USBOM), State geological surveys, and the mining industry. The USBOM uses USGS estimates of undiscovered mineral resources to analyze potential mineral supplies, and the land-managing

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n response to a high-priority request

from the U.S. Forest Service (USFS), the USGS assessed undiscovered mineral resources of 1.4 million acres of contiguous parts of the Gallatin and Custer National Forests in southwestern Montana. The USFS is using this information to develop comprehensive land- and resource-management plans for the Absaroka-Beartooth area, which lies within the Greater Yellowstone ecosystem.

The USGS provided quantitative

estimates of undiscovered mineral resources to enable the USFS to evaluate the significance of the mineral potential. Most of the identified and estimated undiscovered resources of platinum, palladium, and chromium in the United States occur in the Absaroka-Beartooth study area. The USGS estimates that an additional 3,000 metric tons of platinum and palladium resources and 4 million metric tons of chromium resources are present in extensions of known deposits. Mean probabilistic estimates (in metric tons) for gross in-place undiscovered mineral resources include 200 tons of gold, 2,000 tons of silver, 130,000 tons of

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For more information about the Deep Continental Studies program, contact

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Identified resources are defined as resources whose location, quality, and quantity are known or estimated from specific geologic evidence. Identified resources may be economic, marginally economic, or subeconomic. Identified resources include demonstrated (measured and indicated) and inferred resources.

Estimated undiscovered resources are defined as resources whose existence is only postulated; these postulated resources may be in deposits that are economic, marginally economic, or subeconomic.

molybdenum, 230,000 tons of nickel, 6.5 million tons of copper, and more than 6.5 million tons of chromium.

In this assessment, the USGS delineated a favorable tract for the occurrence of gold deposits on the basis of historical mining and exploration and a distinctive geologic environment in the southwestern part of the study area near Jardine, Mont. The USGS estimated a 50-percent probability that the tract contains at least 8.1 metric tons of gold in undiscovered deposits. Commercial exploration that started before the USGS study resulted in an announcement of a new discovery within the tract at Crevice Mountain that contains preliminary drill-indicated reserves of 12.4 metric tons of gold.

Among the results of the AbsarokaBeartooth study are new maps showing the geology, aeromagnetic and gravity data, and stream-sediment geochemical anomalies. Locations of mines, prospects, mineral occurrences, and tracts favorable for various types of mineral deposits also are included. Because these data are shown at the map scale used by the USFS (1: 126,720), they can be easily incorporated into the USFS planning process as base maps for ecosystem management. The results of the USGS study are published in “Mineral-Resource Assessment of the Absaroka-Beartooth Study Area, Custer and Gallatin National Forests, Montana" (USGS Open-File Report 93–207).

Mineral Studies Help Protect Habitat

he USGS published a mineral

resource assessment requested by the Bureau of Land Management (BLM) for use in land-planning efforts to protect the habitats of the desert tortoise and the Mohave ground squirrel in the western Mojave Desert of southern California. The Western Mojave Management Area has been the site of mineral exploration and mining activity since the early 1800's. The USGS report (Open-File Report 92–595, “Evaluation of Selected Metallic and Nonmetallic Mineral Resources, West

Mojave Management Area, Southern California") provides quantitative estimates of undiscovered gold, silver, copper, borate, lead, zinc, tungsten, iron, and molybdenum and qualitative descriptions of undiscovered saline, zeolite, and clay resources. The estimated value of undiscovered borate salts, which are used primarily in manufacturing glass fibers for insulation and textiles, is larger than that of all other quantified resources combined. USGS estimates of undiscovered mineral resources assist the BLM in developing reserve management plans that provide for multiple resource use while maintaining the viability of critical habitat areas for the desert tortoise and the Mohave ground squirrel.

Mineral-Environmental Investigations

M.". studies apply geological, geochemical, and geo

physical expertise to environmental challenges such as establishing geochemistry baselines, characterizing natural and human-induced hazardous sites, and predicting potential environmental impacts caused by mining. Studies underway for several ongoing mineral-resource assessments include: • In the Routt National Forest in northern Colorado, the USGS is conducting acid-mine drainage studies and analyzing stressed vegetation downwind from a powerplant. • The USGS is comparing the soil and water chemistry of samples collected during FY 1993 with the chemistry of baseline samples collected before the recent opening of a smelter near the BLM's Mimbres Resource Area in southwestern New Mexico. • In the Wenatchee National Forest in northeastern Washington, USGS scientists are comparing the geochemistry of natural drainage and mine drainage. • A comprehensive mineralenvironmental assessment is being prepared to complete the mineral-resource assessment of the San Juan National Forest in southwestern Colorado.

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