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Because a map conveys information visually, it is often the best way to present facts about the size, shape, and appearance of our world and about the changes that people have imposed on the world. Some world maps show the mountains, rivers, oceans, and plains that make up the face of the Earth. Some show only the boundaries that divide our world into nations. Others show the Earth's resources, population centers, or areas of earthquake activity.
If a schoolboy asked this question, you would answer it easily enough. "Why, water is a liquid found in and around the earth. Water is the sea, lakes, streams, springs and what comes gushing out of the tap when we turn it on." If he still looks a little unsatisfied, you would explain that our bodies are three-fourths water, and that water covers threefourths of the earth's surface. But you would have to admit to yourself that these facts, interesting as they are, do not quite answer the boy's question: "What is water?"
When the first Earth Resources Technology Satellite (ERTS-A) flies in 1972, NASA expects to receive and bulk-process 9,000 images a week. From this deluge of images, a few will be selected for precision processing; that is, about 5 percent will be further treated to improve the geometry of the scene, both in the relative and absolute sense. Control points are required for this processing. This paper describes the control requirements for relating ERTS images to a reference surface of the earth. Enough background on the ERTS-A satellite is included to make the requirements meaningful to the user.
The United States contains a great variety of landforms which offer dramatic contrasts to a cross-country traveler. Mountains and desert areas, tropical jungles and areas of permanently frozen subsoil, and deep canyons and broad plains are examples of the Nation's varied surface. The presentday landforms the features that make up the face of the Earth are products of the slow sculpturing actions of streams and geologic processes that have been at work throughout the ages since the Earth's beginning.
The structure of the Earth’s crust (the outer shell of the earth above the M-discontinuity) has been intensively studied in many places by use of geophysical methods. The velocity of seismic compressional waves in the crust and in the upper mantle varies from place to place in the conterminous United States. The average crust is thick in the eastern two-thirds of the United States, in which the crustal and upper-mantle velocities tend to be high. The average crust is thinner in the western one-third of the United States, in which these velocities tend to be low. The concept of eastern and western superprovinces can be used to classify these differences. Crustal and upper-mantle densities probably vary directly with compressional-wave velocity, leading to the conclusion that isostasy is accomplished by the variation in densities of crustal and upper-mantle rocks as well as in crustal thickness, and that there is no single, generally valid isostatic model. The nature of the M-discontinuity is still speculative.
Global change is a relatively new area of scientific study using research from many disciplines to determine how Earth systems change, and to assess the influence of human activity on these changes. This teaching packet consists of a poster and three activity sheets. In teaching these activities four themes are important: time, change, cycles, and Earth as home.
Some water underlies the Earth's surface almost everywhere, beneath hills, mountains,plains, and deserts. It's not always accessible, or fresh enough for use without treatment, and it's sometimes difficult to locate or to measure and descri be. This water may occur close to the land surface, as in a marsh, or it may lie many hundreds of feet below the surface, as in some arid areas of the West. Water at very shallow depths might be just a few hours old ; at moderate depth, it may be 100 years old; and at great depth or after having flowed long distances from places of entry, water may be several thousands of years old . Water under the Earth's surface is called ground water.
Oceans are the largest geographic feature on the surface of the Earth, covering approximately 70% of the planet's surface. As a result, oceans have a tremendous impact on the Earth, its climate, and its inhabitants. The coast or shoreline is the boundary between ocean environments and land habitats. By the year 2025, it is estimated that approximately two-thirds of the world's population will be living within 200 kilometers of a coast. In many ways, we treat the coast just like any other type of land area, as a safe and stable place to live and play. However, coastal environments are dynamic, and they constantly change in response to natural processes and to human activities.
Policy makers, managers, scientists and the public can view the changing environment using satellite images. More than 60 Earth observing satellites are collecting images of the Earth's surface. Remote sensing satellite systems for land cover assessment are operated by a growing number of countries including India, the United States, Japan, France, Canada and Russia. The focus of this publication is satellite systems for land cover monitoring. On the reverse is a table that compares a selection of these systems, whose data are globally available in a form suitable for land cover analysis. We hope the information presented will help you assess the utility of remotely sensed image to meet your needs.
Umnak Island is a dumbbell-shaped island in the eastern part of the Aleutian Islands. The island is 70 miles long and trends northeast-southwest. During 1946 volcano investigations were begun on the island and geologic mapping of most of northeastern Umnak Island was completed. Okmok Volcano, a large, broad volcanic mountain rising to altitudes of 3,000 to 3,500 feet, occupies the central portion of northeastern Umnak Island. Fort Glenn, and Army airbase, is situated on the eastern end of the island, approximately 9 miles east of Okmok Volcano. The central part of Okmok Volcano is indented by Okmok caldera, a large cliff-rimmed volcanic depression, 7%, miles in maximum diameter. The floor of the caldera is 1,500 to 2,500 feet below the caldera rim. Nine large cinder cones and many small ones lie on the caldera floor, chiefly along two arcuate zones. The caldera is drained by Crater Creek, which flows through a deep gorge cut in the northeastern wall of the caldera, and into Bering Sea. Mount Tulik (4,111 feet altitude) and Mount Idak (1,918 feet altitude) arc important centers of ancient volcanism on the flanks of Okmok Volcano. The geologic history of Okmok Volcano falls into three stages: The first includes the upbuilding of an ancient cone—Mount Okmok—to an altitude of at least 6;500 feet on the site of the present caldera; the second encompasses the destruction in a castastrophic eruption of the summit cone and the formation of the caldera; the third comprises events since the great eruption. The earliest activity at Mount Okmok probably dates hack to the late Tertiary period. A composite cone, concave-sided in profile, was built by the alternate eruption of ash, coarse pyroclastics, and basalt flows. During the late Pleistocene, volcanic activity at Mount Okmok was greatly reduced and a topography of late youth was carved on the lower slopes by streams and valley glaciers. The summit of Mount Okmok was upwarped and dikes and necks were injected into the resulting fractures. A large volcano at the site of Mount Idak was active during part of the period of upbuilding at Mount Okmok but became extinct during the middle Pleistocene. A parasitic vent, Mount Tulik, became active during the late Pleistocene and built a steep-sided cone before it became extinct, shortly before the formation of Okmok caldera. A cataclysmic eruption terminated the period of dissection at Mount Okmok, 10,000 or more years ago. Part of the summit was blown away by the explosive violence of this eruption. Nuees ardentes (glowing clouds) and mudflows deposited tuff-breccia and agglomerate in the glacial valleys; later phases of the eruption blanketed the landscape with ash. Near the end of the eruption, the remaining upper part of the volcano collapsed along arcuate fractures: large blocks subsided several thousand feet and are now concealed in the caldera Poor beneath later deposits. A large arcuate fault block which subsided less than other blocks stands above the floor in the northeastern part of the caldera. After the eruption, water collected in the caldera, forming a lake. Small but frequently active cones built islands in the lake and covered its bottom with pyroclastic debris. The lake eventually overflowed the lowest point in the rim of the caldera, and Crater Creek Gorge was carved, draining the lake and dissecting its deposits. Renewed movement along faults at the head of Crater Creek Gorge later raised a harrier which temporarily dammed the drainage and formed a second caldera lake. Readjustments among subsided blocks in the caldera floor resulted in the folding of postcaldera deposits at several localities. Much of the caldera floor has been covered by lava flows extruded from several cones since the draining of the first caldera lake. In general, however, volcanic activity seems to have declined since the great caldera-forming eruption. Seven eruptions from cones on the caldera floor have been recorded since 1817; the latest occurred in 1945. As part of the geochemical program for the study of Okmok Volcano, temperatures of fumaroles were measured and samples of the products of the volcanic activity were analyzed. Average temperatures of fumaroles at one source of the 1945 lava low dropped from 320° C. on July 19 to 90° C. on September 5. The temperatures of fumaroles associated with the crater vents on both Cones A and C ranged from 95° C. to 97" C., which is slightly below the condensation point of steam, indicating the presence of minor quantities of gases other than steam. The magmatic gases of fumaroles on Cone A consisted of carbon dioxide and sulfur dioxide in about equal amounts. The lack of halogen acid gases in the fumaroles and the steadily dropping temperatures arc interpreted as indicating that the present quiescence of Cone A will continue for many months. Solid reaction products from areas of fumarolic activity on Cone A are sulfates of sodium, calcium, and iron. The presence of hydrogen sulfide as the dominant sulfur gas at Cone C is interpreted as indicating the dying stages of the present cycle of activity of Cone C. Thermal springs along the north base of Cone D have a total discharge of 115 cubic feet per second. Their average temperature is approximately 7° C. above the annual mean. From these figures it is calculated that about 21,000 kilogram calories per second are being given off by Cone D. The spring waters contain minute quantities of boron which is indicative of a magmatic source for a small part of the water. Hence, Cone D though quiescent is not extinct. Evidence is presented to show that most of the spring water from Cone D is meteoric in origin. Thermal waters in the southwestern part of Umnak Island at Hot Springs Cove and south of Geyser Bight contain lithium, boron, arsenic, and antimony in solution. These elements are regarded as derived from underlying magmas that are in an advanced state of crystallization and hence not likely to give rise in the near future to large-scale volcanic activity. Three portable seismographs were placed on the flanks of Okmok Volcano and were in operation during most of the period from June 1 to October 1. During this period several slight tremors and one moderate tremor, all of distant origin, were registered, but no tremors attributable to Okmok Volcano were recorded. The lack of tremor records, however, may have been due more to the insensitivity of the instruments than to the absence of tremors. Earth-current investigations were carried on during August and September by comparison of records obtained from a base station at Fort Glenn with those from a station 1 V2 miles southwest of Mount Tulik. The records obtained indicate that no difference in magnitude or direction of earth currents existed between the Fort Glenn and Mount Tulik areas. The similarity of record obtained is indicative of the absence of a disturbing factor such as a large body of live magma beneath Okmok Volcano. Future eruptions of Okmok Volcano are expected to he of mild to moderate intensity, and will he chiefly in the form of ash falls from vents inside the caldera. There would be a great menace—in the form of lava flows, nuees ardentes, and mudflows—to installations at Fort Glenn if a new center of volcanism came into existence on the east slope of Okmok Volcano. Small postcaldera cones now exposed there indicate that extra-caldera eruptions have occurred in the recent past and can be expected in the future. The possibility of another catastrophic eruption of the caldera-forming type, however, is remote. Okmok Volcano should be kept under close observation, partly because of its possible threat to Fort Glenn and partly because it is a readily accessible locale for accumulating information on details of volcanic processes, applicable to other volcanoes in the Aleutian arc and elsewhere.
The Global Land Information System (GLIS) is an interactive computer system developed by the U.S. Geological Survey (USGS) for scientists seeking sources of information about the Earth's land surfaces. GLIS contains "metadata," that is, descriptive information about data sets. Through GLIS, scientists can evaluate data sets, determine their availability, and place online requests for products. GLIS is more, however, than a mere list of products. It offers online samples of earth science data that may be ordered through the system.
After decades of using only one map projection, the Polyconic, for its mapping program, the U.S. Geological Survey (USGS) now uses sixteen of the more comnon map projections for its published maps. For larger scale maps, including topographic quadrangles and the State Base Map Series, conformal projections such as the Transverse Mercator and the Lambert Conformal Conic are used. On these, the shapes of small areas are shown correctly, but scale is correct only along one or two lines. Equal-area projections, especially the Albers Equal-Area Conic, and equidistant projections which have correct scale along many lines appear in the National Atlas. Other projections, such as the Miller Cylindrical and the Van der Grinten, are chosen occasionally for convenience, sometimes making use of existing base maps prepared by others. Some projections treat the Earth only as a sphere, others as either ellipsoid or sphere. The USGS has also conceived and designed several new projections, icluding the Space Oblique Mercator, the first map projection designed to permit mapping of the Earth continuously from a satellite with low distortion. The mapping of extraterrestrial bodies has resulted in the use of standard projections in completely new settings. With increased computerization, it is important to realize that rectangular coordinates for all these projections may be mathematically calculated with formulas which would have seemed too complicated in the past, but which now may be programed routinely, if clearly delineated with numerical examples. A discussion of appearance, usage, and history is given together with both forward and inverse equations for each projection involved.
Within 150 years, Yosemite has moved from great obscurity to worldwide fame as one of the most visited of our national parks. As a remarkable place where people can enjoy unparalleled scenes of natural beauty and where many easily observed geologic features are concentrated, the park is rivaled by few other areas on the planet. The majesty and immense variety of these features have inspired artists and photographers, intrigued tourists, and stirred controversy among geologists. Field studies in the Yosemite area have contributed to the development of our ideas about geologic processes, including the different actions of streams and glaciers in the evolution of the landscape, and the formation of granite, the basic bedrock of much of the Earth's continents. The park's role as a natural laboratory for geologic research cannot be overemphasized, and its investigation has led to many landmark studies by U.S. Geological Survey geologists over the past 70 years. In 1913, the first detailed program of research on the geology of the park and the origin ofYosemite Valley was begun by Francois Matthes and Frank Calkins. Their work, along with that of later generations of Survey geologists, myself included, serves as the basis for our present understanding of the geologic history of Yosemite and of the processes that formed and continue to mold its landscape. This book, which makes available in one volume a comprehensive summary of the current geologic knowledge of Yosemite National Park, is an excellent example of the Survey's continuing effort to provide earth-science information in the public service.
The rocks of the East Mojave National Scenic Area (EMNSA) record a history of dynamic geologic events that span more than 1,800 million years (m.y.). These geologic events contributed significantly to development of the spectacular vistas and panoramas present in the area today. The oldest rocks underlie much of the northern part of the EMNSA. These rocks were subjected to extreme pressures and temperatures deep in the Earth's crust about 1,700 million years ago (Ma). They were subsequently intruded by granitic magmas from about 1,695 to 1,650 Ma, by additional granitic magmas at about 1,400 Ma and, later, at about 1,100 Ma, by iron-rich magmas that crystallized to form dark igneous rocks termed diabase. Unusual potassium- and magnesium-rich rocks, emplaced at about 1,400 Ma, crop out in a few places within and near the EMNSA. Their distinctive composition results from very small degrees of partial melting of mantle peridotite that was highly enriched in incompatible trace elements. At Mountain Pass, just outside the northeast boundary of the EMNSA, the potassium- and magnesium-rich rocks are accompanied by a rare type of carbonatite, an igneous rock composed of carbonate minerals, that contains high-grade rare earth element mineralization. Subsequent to these igneous-dominated events, sedimentary strata began to be deposited at about 1,000 Ma; mostly sandstone and shale were deposited initially in marine and, less commonly, in continental environments along the west edge of the core of the North American continent. Sedimentation eventually culminated in the widespread deposition of thick marine limestones from about 400 to about 245 Ma. These limestones represent a continental-shelf environment where shallow-water limestone formed to the east and deeper water limestone formed to the west. The end of the formation of these sedimentary deposits probably was caused by uplift of the shelf, which marked the beginning of a long period of tectonic upheaval. At about 170 Ma, widespread emplacement of coarse-grained granitic magmas began again in the region; some of these magmas also erupted as volcanic rocks. Additional episodes of magmatism took place at about 100 Ma and at 75 Ma. Most of the metallic-mineral occurrences in the EMNSA are associated with the igneous rocks that range in age from 170 to 75 Ma. During each of these magmatic events, the previously deposited sedimentary strata were buckled and broken as the entire region, part of a continental-scale fold and thrust belt, underwent crustal shortening and compression. A period of tectonic quiescence characterized the region from about 65 Ma to about 20 Ma. The quiet period ended abruptly with widespread volcanism along the southern and eastern parts of the EMNSA. The major gold deposits in the Castle Mountains are associated with this episode of volcanism. During this volcanic outburst, the crust extended laterally in several areas that border the EMNSA: along the lower Colorado River 65 km to the east, in the Kingston Range 20 km to the north, and in the central Mojave Desert 75 km to the southwest. This extensional deformation is characterized by the superposition of upper-crustal rocks over midcrustal rocks along large flat-lying faults, several of which project beneath rocks now exposed at the surface in the EMNSA. The near-surface rocks of the EMNSA, however, apparently escaped much of this intense extensional deformation. High-angle faults, which cut several of the mountain ranges, possibly have undergone several periods of movement, which date back to approximately 70 to 100 Ma. Some faults are of local importance to the physiographic development of the mountain ranges and intervening basins, and, in places, the faults seem to have localized various kinds of ore bodies and mineral occurrences. Volcanism and extensional deformation waned from 14 to 11 Ma. By approximately 10 Ma, widespread erosion had produced broad erosional dome-shaped mountains in the n
A National Association of Geoscience Teachers Far Western Section (NAGT-FWS) field conference is an ideal forum for learning about the geology and natural history of the San Francisco Bay area. We visit classic field sites, renew old friendships, and make new ones. This collection of papers includes field guides and road logs for all of the Bay-area trips held during the NAGT-FWS 2001 Fall Field Conference and supplemental chapters on other aspects of the area’s natural and human history. The trips touch on many aspects of the geology and natural hazards of the Bay area, especially urban problems associated with living on an active tectonic plate margin: earthquake faults, coastal erosion, landslides, and the utilization of land and natural resources. We hope this conference not only provides a two-day learning opportunity for conference participants but that students and educators will use this field guidebook for future teaching and research. Many thanks are due to the U.S. Geological Survey (USGS) and San José State University (SJSU) for cohosting the conference. We are grateful to each of the field trip leaders for preparing the trips and writing the accompanying guides. We especially appreciate the many hours put in by the guidebook reviewers, Robert I. Tilling (USGS) and Paula Messina (SJSU), and to the USGS Western Publications Group for editing, layout, and web posting. Additional guidebook contributions include articles by John Galloway, Scott Starratt, Page Mosier, and Susan Toussaint. During the conference guest speakers include Robert I. Tilling (USGS Volcano Hazards Team) and Ross Stein (USGS Earthquake Hazards Team). Workshops prepared for the conference include GIS in the classroom, using USGS data by John Vogel (USGS) and Paula Messina (SJSU), and The Best of BAESI (Bay Area Earth Science Institute), a teacher training organization under the direction of Ellen Metzger (SJSU) and Richard Sedlock (SJSU). The conference provides an opportunity to showcase USGS scientific and education resources with self-guided tours of the USGS Library, the Earth Science Information Center (ESIC), the Visitor Center, and various laboratories on the USGS campus and includes a half-day participatory tour of the USGS research vessel the R/V Polaris and the USGS Marine Facility at the Port of Redwood City under the direction of Cynthia L. Brown, Francis Parchaso, and Tara Schraga. Beyond the names mentioned above, a host of USGS and SJSU staff, SJSU students, and NAGT-FWS members contributed to the preparation and orchestration of the conference. We couldn’t have done it alone. Leslie C. Gordon (USGS), Philip W. Stoffer (USGS), and Deborah Harden (SJSU) NAGT-FWS 2001 Fall Field Conference Organizers.
An understanding of our fragile environment can begin with a recognition of the importance of certain elements, commonly called "minerals substances" (such as iron and zinc), in the lives of humans and animals and in the soils that support plants. This recognition is well deserved because these elements are essential for the life or optimum health of an organism. Some elements such as carbon, hydrogen, oxygen, magnesium, potassium, and phosphorus are required in relatively large amounts by organisms. However, others are required in smaller quantities; these are referred to as trace elements. Diseases have been related to the deficiency of about 20 elements in animals and humans and to the deficiency of approximately 13 elements in plants. At the same time, if these and other elements occur in quantities great enough, toxicity can result. An element, or any substance, that occurs in the environment and contains concentrations above what are considered to be background levels may be considered a contaminant. When contaminants occur at levels that are potentially harmful to organisms, they are labeled as hazards. Often the quantitative difference between essential amounts and toxic concentrations of these elements is very small. For example, the trace element selenium is required at a level of no less than 0.4 ppm in the diet of cattle but can be toxic at levels greater than approximately 4ppm. Elements that are required for survival by animals and plants are termed essential, while those not required are nonessential. Trace essential elements such as fluorine, copper, selenium, molybdenum, and others listed in the table on page 1 can be hazardous to life forms if present at high levels. Nonessential heavy metals such as arsenic, lead, mercury, cadmium, and chromium are usually toxic to organisms at much lower levels than trace essential elements. Depending on the association that these nonessential elements may form with natural geologic materials such as organic matter, other elements or minerals, and adsorbers (such as clays), these elements can range from being safe to being extremely toxic. The elemental composition of plants, animals, and humans correlates with the geologic makeup of the Earth, and life has evolved reflecting these natural occurrences. The science of environmental geochemistry examines the interrelationship of life with the physical and chemical Earth.
The USGS Coastal and Marine Geology Program has large-scale national and regional research projects that focus on environmental quality, geologic hazards, natural resources, and information transfer. This Circular highlights recent scientific findings of the program, which play a vital role in the USGS endeavor to understand human interactions with the natural environment and to determine how the fundamental geologic processes controlling the Earth work. The scientific knowledge acquired through USGS research and monitoring is critically needed by planners, government agencies, and the public. Effective communication of the results of this research will enable the USGS Coastal and Marine Geology Program to play an integral part in assisting the Nation in responding the pressing Earth science challenges of the 21st century.
The 2004 Joint Northeast-Southeast Section Meeting of the Geological Society of America is the fourth such meeting and the third to be held in or near Washington, D.C. This guidebook and the field trips presented herein are intended to provide meeting participants, as well as other interested readers, a means to understand and enjoy the rich geological and historical legacy of the National Capital Region. The field trips cover all of the major physiographic and geologic provinces of the central Appalachians in the Mid-Atlantic region. Trip 1 outlines the tectonic history of northern Virginia along an east-to-west transect from the Coastal Plain province to the Blue Ridge province, whereas the other field trips each focus on a specific province. From west to east, these excursions investigate the paleoclimate controls on the stratigraphy of the Paleozoic rocks of the Allegheny Plateau and Valley and Ridge province in West Virginia, Pennsylvania, and Maryland (Trip 3); Eocene volcanic rocks that intrude Paleozoic rocks in the westernmost Valley and Ridge province in Virginia and West Virginia (Trip 4); age, petrology, and structure of Mesoproterozoic gneisses and granitoids located in the Blue Ridge province within and near Shenandoah National Park, Virginia (Trip 2); the use of argon data to unravel the complex structural and thermal history of the metamorphic rocks of the eastern Piedmont province in Maryland and Virginia (Trip 5); the use of cosmogenic isotopes to understand the timing of bedrock incision and formation of terraces along the Potomac River in the eastern Piedmont province near Great Falls, Virginia and Maryland (Trip 6); the nature of the boundary between rocks of the Goochland and Chopawamsic terranes in the eastern Piedmont of Virginia (Trip 7); the role of bluffs and fluvial terraces of the Coastal Plain in the Civil War Battle of Fredericksburg, Virginia (Trip 8); and the Tertiary lithology and paleontology of Coastal Plain strata around the Chesapeake Bay of Virginia and Maryland (Trip 9). Some of the field trips present new geochronological research that uses isotopic techniques to unravel Earth history and processes, including U-Pb dating to determine the timing of metamorphism and igneous activity associated with the Mesoproterozoic Grenville orogeny (Trip 2); argon (4DAr/39Ar) analysis to understand the complex Paleozoic history of deformation and metamorphism in the Piedmont (Trip 5); and cosmogenic beryllium-10 data to derive exposure ages of landforms and deposits of the Potomac River valley (Trip 6). Several trips shed insight on significant or enigmatic geologic features of the region. Trip 3 presents evidence for global paleoclimate controls on the Paleozoic stratigraphy of the Appalachian basin, including evidence for Late Devonian glacial deposits. Trip 4 investigates unusual Eocene igneous rocks in the Eastern United States, and Trip 2 visits several local ductile high-strain zones, offering geologists opportunities to consider the importance of such structures relative to the poorly understood Rockfish Valley fault zone in the Blue Ridge province. In the Piedmont province, Trip 7 focuses on a controversial terrane boundary, whereas Trip 5 crosses several lithologic belts with distinct thermotectonic histories that suggest terrane boundaries. Trip 6 sheds new light on the erosional history of a major river gorge cut into crystalline rocks in the Fall Zone. Four trips are recommended for Earth science teachers and are cosponsored by the National Association of Geologic Teachers (NAGT). These trips focus on the tectonic history of northern Virginia (Trip 1), terraces of the Potomac River at Great Falls and cosmogenic isotope analysis to date the terraces and the incision history (Trip 6), and Tertiary lithology and paleontology of the Chesapeake Bay region (Trip 9). Trip 8 takes advantage of the rich Civil War history of this region to look at the role that geology played in the strategies and outcome of the Battle of Fredericksburg. This guidebook is the result of much hard work by many individuals. The editors wish to thank the field trip leaders and authors, the technical reviewers, and Nancy Stamm of ths USGS Geologic Names Committee. We also owe a very special thanks to Linda Gundersen, Chief Scientist, Geologic Discipline, USGS, who provided funding for the guidebook.