Booklets: G - N

	Gemstones An overview of the production of specific U.S. gemstones. Online version
	Global Environment Outlook 2000 Published by United Nations Environmental Programs, this multilingual book reports periodic reviews of the state of the world's environment, identifying major environmental concerns, trends, and emerging issues together with their causes, and their social and economic impacts. Online version
	The Geologic History of Cape Cod, Massachusetts Cape Cod, a sandy peninsula built mostly during the ice age, juts into the Atlantic Ocean like a crooked arm. Geologists are interested in Cape Cod because it was formed by glaciers, very recently, in terms of geologic time, and because the shore is ever changing as the Cape adjusts to the rising sea. Online version
	The Geologic Story of the Ocoee River Over millions of years, the Ocoee River has cut a steep, winding channel into a mountainside of hard rock. As you travel through the Ocoee River Gorge along U.S. Highway 64 in the scenic Cherokee National Forest of southeastern Tennessee, take some time to look at the rocks along the way. Online version Companion brochure: Geology of the Ocoee Whitewater Center, Cherokee National Forest
	Geologic Time This 20-page booklet explains relative and radiometric time scales and how geologists measure the age of the Earth. Illustrates the scientific processes that are used to interpret the Earth's geologic history. 94-0121 Online version
	The Geology of Radon This 28-page booklet presents geological information about radon, including how it forms, the kinds of rocks and soils it comes from, and how it moves through the ground or is carried by water. Geologists also explain in the booklet how they estimate the radon potential of an area. 94-0115 Online version
	Glaciers: Clues to Future Climate A glacier is a large mass of ice having its genesis on land and represents a multiyear surplus of snowfall over snowmelt. At the present time, perennial ice covers about 10 percent of the land areas of the Earth. Although glaciers are generally thought of as polar entities, they also are found in mountainous areas throughout the world, on all continents except Australia, and even at or near the Equator on high mountains in Africa and South America. Online version
	Glimpses of the Ice Age from I-81 Travelers on Interstate Highway 81 can see remnants of the Ice Age on the mountains between Strasburg and Harrisonburg, Virginia. Scattered along the miles of green, forested mountains are many gray patches without any forests. These treeless patches, or openings, in the steep mountain forests are block fields -- geologic features that owe their origin to the Ice Age. Online version
	Gold Through the ages men and women have cherished gold, and many have had a compelling desire to amass great quantities of it--so compelling a desire, in fact, that the frantic need to seek and hoard gold has been aptly named "gold fever." Gold was among the first metals to be mined because it commonly occurs in its native form, that is, not combined with other elements, because it is beautiful and imperishable, and because exquisite objects can be made from it. Text-only version
	The Great Ice Age The Great Ice Age, a recent chapter in the Earth's history, was a period of recurring widespread glaciations. Mountain glaciers formed on all continents, the icecaps of Antarctica and Greenland were more extensive and thicker than today, and vast glaciers, in places as much as several thousand feet thick, spread across North America and Eurasia. Online version
	Ground Water Learn how ground-water occurs and what we need to do to keep it clean. Online version PDF version
	Ground Water and the Rural Homeowner This 36-page booklet provides the rural homeowner with a basic description of ground-water and problems one may expect to encounterwhen building, such as contamination from septic systems and lowered well-water levels. 94-0055
	Helping Your Child Learn Geography This 32-page booklet, published in cooperation with the U.S. Department of Education and the National Geographic Society, is designed to help parents stir children's curiosity about geography. The activities can also be used in the classroom. The activities are designed for children 5-10 years of age. 94-0130 Online version
	How Vulnerable Are Seattle Area Lifelines? Like any modern urban area, the greater Seattle area depends on highways, railroads, pipelines, ports, airports, communications, and the electrical power system to sustain its economic life. Many of these critical lifelines lie across the path of faults. Online version
	The Interior of the Earth Three centuries ago, Sir Isaac Newton determined that the average density of the Earth is twice that of surface rocks and that the Earth's interior, therefore, must be composed of much denser material. Our knowledge of what's inside the Earth has improved immensely since Newton's time, but his estimate of the density remains essentially unchanged. This brochure presents current information on what makes up the interior of our planet. Online version
	Land Use History of North America: A context for Understanding Our Changing Environment This Web site addresses questions for several regions of North America, such as: What types of changes are occurring now, and how fast are they occurring? How do these changes compare with those in the past, and what does it all mean for future environmental quality and the habitability of the planet? Online version
	Man Against Volcano: The Eruption on Heimaey, Vestmannaeyjar, Iceland One of the most destructive volcanic eruptions in the history of Iceland began in the early morning of January 23,1973, near the country's premier fishing port, the town of Vestmannaeyjar, on Heimaey, the only inhabited isle in the Vestmannaeyjar volcanic archipelago. This booklet discusses the impact of the 1973 volcanic eruption of Eldfell on the island of Heimaey. Before the eruption was over, approximately one-third of the town of Vestmannaeyjer had been obliterated; but, more importantly, the potential damage probably was reduced by the spraying of seawater onto the advancing lava f!ows, causing them to be slowed, stopped, or diverted from the undamaged portion of the town. Online version
	Monitoring Active Volcanoes Centuries ago, the Romans attributed volcanic and related phenomena (including earthquakes) mainly to the movement of wind imprisoned inside the Earth rushing violently to the surface. Today, scientists know that volcanic eruptions occur when buoyant magma (molten rock) that formed deep in the Earth ascends to the surface and ultimately is ejected upon release of gas pressure. With precise instruments and refined data analysis, it is now possible to track the subsurface movements of magma by monitoring the earthquakes and measuring the ground changes that accompany such movements. Online version
	The Mountain That Moved Prehistoric, giant landslides in Montgomery and Craig Counties, Va., in the Blacksburg/Wythe Ranger Districts of the Jefferson National Forest, are the largest known landslides in eastern North America and are among the largest in the world. One of the landslides is more than 3 miles long! The ancient, giant landslides extend for more than 20 miles along the eastern slope of Sinking Creek Mountain. Enormous slabs of rock ranging from about 0.2 to more than 1.5 square miles in size broke loose and slid downslope under the influence of gravity. The movement of some slides may have been slow, but the movement of others was probably sudden and catastrophic. Online version
	Natural Gemstones This 16-page booklet describes mineral and organic gemstones. It gives values of U.S. production of natural and synthetic minerals versus imports, as well as gemstone chemical formulas. Selected references are also supplied. Online version (Web only)