Nature has blessed and in some ways cursed the United States. No country on Earth can match America's diverse physical conditions and the resulting natural landscapes. The United States holds the distinction of being the only country that has within its territory all of the world's climates and ecosystems (a combination of climate, natural vegetation and animal life, soils, and water features). From the vast and productive “fruited plains” to the “purple mountain majesties” described in Bates's “America the Beautiful,” the United States is home to some of the world's largest and most stunning landform features. The country possesses a veritable cornucopia of natural resources. They have been a key factor behind the phenomenal development that has made the United States the world's leading economic powerhouse. Rivers, lakes, and groundwater supplies have provided ample water for domestic, agricultural, and industrial use. The Mississippi River system, the Great Lakes, and multiple outlets to the global sea give the United States the world's most extensively used navigation network. In terms of its physical geography, the United States truly is a land of superlatives!
A variety of natural environmental conditions afford a country many options for different land uses and kinds of economic development. Crops, for example, are adapted to different types of climate and soil. Because of the environmental diversity in the United States, any crop in the world can be grown somewhere in the country. Even terrain plays an important role. The “amber waves of grain” to which Bates referred depend on vast, relatively flat land holdings that can be farmed with large agricultural equipment. Within the context of a particular culture, certain environmental conditions can be important. Natural harbors located at or near river mouths, for example, are extremely important to a country that is engaged in manufacturing and commerce on a global scale. Mountain scenery, steep slopes, and a deep snowpack are important to people who are affluent and mobile enough to enjoy vacations, skiing, and perhaps even living in a scenic landscape.
Nature presents many challenges, as well as opportunities. The United States is unique in that it is also the only country in the world that is subject to the wrath of all natural hazards. Such events—whether geologic, weather related, waterborne, fire related, or the result of some other natural element—can and often do pose a serious threat to life and property.
This chapter focuses on both nature and cultural ecology. Cultural ecology, simply defined, is the relationship that humans—based on their culture (needs, technology, capital resources, economic system, and so forth)—establish with the natural environment(s) in which they live. The study of such relationships is one of the most fundamental geographic themes. Each environment offers a variety of opportunities and challenges, although humans can often add what nature has not provided. Irrigated agriculture, the building of dams and reservoirs and the uses of both, and importing petroleum and other resources serve as examples.
Despite its environmental diversity, the basic way of life practiced by Americans is fairly similar regardless of the location. When thinking about cultural ecology, geographers seek answers to three questions. First, how do people adapt to the environments in which they live? Such patterns often vary greatly from culture to culture and also change through time. Second, what natural elements are important to a people and how are natural resources used? A splendid example of differing perceptions is provided by Alaska's Arctic National Wildlife Refuge (ANWR). Many European Americans value the area's great potential to produce petroleum and natural gas. On the other hand, some native peoples value the caribou herds on which their culture was largely based. Finally, how have humans changed the environments in which they live?
THE LAND AND ITS FEATURES
The United States offers a varied mosaic of landform types—broad plains, rolling hills, rugged plateaus, and majestic mountains. Such diversity offers many opportunities for different types of land use and economic development. Each environment is well suited to some activity, assuming that the culture, technology, and capital resources can support human needs and desires. This reality is reflected in the recent rapid population growth and economic development experienced in areas such as the desert Southwest and the Mountain West. In some areas, such as the Colorado Plateau, aridity and poor soil limit agricultural development, resulting in a very sparse population. However, the region is home to some of the world's most spectacular landform features that result from water erosion: Arizona's Grand Canyon National Park and Utah's Bryce Canyon, Zion, and Arches national parks and Cedar Breaks National Monument. The area's natural wonders attract millions of tourists each year. Our tour of the nation's physiographic areas begins with the Pacific region.
Mountains and Valleys of the Pacific Region
The Pacific region extends from California to Alaska and includes Hawaii. It is home to the country's greatest mountain ranges, its highest (and “tallest”) mountains, and some of the continent's most stunning scenery. Here, all three of nature's land-building processes—volcanism, faulting, and folding—are at work. It is also a region in which the agents of erosion—glaciers and swift-flowing streams, in particular—have sculpted spectacular physical landscapes.
Volcanic activity created the Hawaiian Islands; Alaska's Aleutian Islands and many of its mountains; and the Cascades of northern California and western Oregon and Washington. Volcanism is an ongoing process in each of these regions. In fact, the world's most active and extensively studied volcano is in Hawaii (on the big island) in Volcanoes National Park. There, Kilauea Crater “erupts” continuously, although in a gentle, bubbling, non-life-threatening fashion. Two other high peaks on the tropical island of Hawaii occasionally have caps of snow. Hawaii's highest peak, Mauna Kea, rises about 20,000 feet (6,096 meters) from the Pacific floor and reaches an elevation of 13,796 feet (4,205 meters) above sea level. Measured from base to peak, it spans a distance of almost 34,000 feet (10,360 meters), making it the world's “tallest” mountain (though obviously not the highest above sea level).
On the mainland, hills and low mountains form a series of coastal ranges. Many of these features are the result of geologic folding, formed by the colliding Pacific and North American tectonic plates. Only in Alaska (in various ranges) and Washington (the Olympic Mountains and National Park) do high mountains hug the coast. Moving inland, uplands give way in several locations to fertile valleys that rank among the country's most productive agricultural areas. They include the Imperial Valley and Central Valley (formed by the combined San Joaquin and Sacramento valleys) in California, Oregon's Willamette Valley, and the lowlands that border Washington's Puget Sound.
A series of high mountain ranges that are part of the Pacific “Ring of Fire” extend from California northward to Alaska and continue into Asia. This region is a zone of geologic instability that includes all lands bordering the Pacific. As the Pacific and other tectonic plates crunch and grind away, they are responsible for more than 80 percent of the world's seismic (earthquake) and volcanic activity.
The Sierra Nevada, central California's towering “backbone,” is an excellent example of an uplifted fault block range.
From its crest, the forest-covered western slope drops gradually over a distance that averages about 80 miles (130 kilometers). The upward-thrust eastern edge of the range features majestic Mount Whitney, a 14,494-foot (4,418-meter) peak that is the highest point in the adjoining 48 states. The eastern escarpment (slope) of the Sierra offers spectacular scenery as it drops more than 14,000 feet (4,267 meters) in a distance of only several miles. Incredibly, about 60 miles (100 kilometers) east of Mount Whitney, Death Valley plunges to a depth of 282 feet (86 meters) below sea level. This is not only the lowest spot of dry land in the Western Hemisphere, it is the third-lowest point of dry land on Earth!
Many of Alaska's towering, snow-clad mountains also are of fault block origin, including the Alaska Range. Here, buried beneath a mantle of snow and glacial ice, Mount McKinley (also called Denali) is North America's highest peak. No mountain can match McKinley's local relief, thereby making it the world's “tallest” (although not the highest) and one of the most imposing peaks above sea level. From a base near sea level, it soars to an elevation of 20,320 feet (6,194 meters) in a distance of about 20 miles (32 kilometers).
Beginning in northern California and extending northward into Washington are the volcano-formed Cascades. The highest peak is spectacular snowcapped Mount Rainier, which rises 14,410 feet (4,392 meters) above the surrounding lowlands. In 1980, the violent eruption of Washington's Mount St. Helens was a stark reminder that the Cascades remain a very active volcanic range. Alaska has more than 100 volcanoes, many of which are extremely active.
Mountains, Plateaus, and Basins of the Interior West
The western interior offers a variety of huge basins, rugged plateaus, deep canyons, and soaring mountains—all of which contribute to some of the nation's most spectacular terrain. Basin-and-range topography dominates the region between the Sierra Nevada and the Cascades and eastward to the Rocky Mountains and western Texas. Here, relatively low and scattered mountain ranges separate broad and relatively flat basins. Many of the basins have interior drainage, or no outward flow. When water flowing into the basins evaporates, salts are left behind to accumulate. Of the many such areas in the American West, Utah's Bonneville Salt Flats is the best known. Some basins contain large saltwater bodies, such as Utah's Great Salt Lake and southern California's Salton Sea. In most basins, though, lakes do not last. They form after a period of rainfall, only to evaporate quickly and disappear, leaving behind a salty encrustation as evidence of their brief existence.
Two huge plateaus occupy the inland Pacific Northwest and the “Four Corners” area of the Southwest. The Columbia Plateau covers portions of eastern Washington, northeastern Oregon, and western Idaho. It is of volcanic origin, formed by magma and lava that poured across the land millions of years ago and accumulated to a depth of up to 6,000 feet (1,829 meters). In addition to its many volcanic features, the plateau offers several other unique landscapes. About one-sixth of its surface is covered by loess, or very fine powderlike material that was deposited by the wind from glacial outwash material during the ice age. This hilly region, the Palouse, contains some of the country's most fertile soil and best wheat-growing land.
The region also has a number of remarkable features scoured by water erosion. Hells Canyon is a yawning 8,000-foot-(2,438-meter-) deep chasm on the Snake River between northeastern Oregon and western Idaho. It is the deepest river gorge in North America, nearly half a mile (one kilometer) deeper than Arizona's Grand Canyon. The Columbia Plateau also is the site of what may be the world's strangest erosional landscape: eastern Washington's “Scablands.”
The Scablands are a lunar-like landscape of bare rock. Thousands of years ago, during the late stages of the ice age, a huge lobe of glacial ice dammed today's Clark Fork River near Sandpoint, Idaho. As water built up behind the barrier, it created ancient Lake Missoula, a water body that extended well into western Montana and reached a depth of about 2,000 feet (610 meters). Ice floats, and eventually, the giant lobe began to rise. This caused an immediate breakup of the ice. The result was an event believed by some scientists to have been the world's most destructive flood. A torrent of water with a volume estimated to have been 10 times that of the entire world's river flow was unleashed. Imagine the destruction as the churning water rushed toward the Pacific Ocean at speeds up to 65 miles per hour (105 kilometers per hour)! The force of the raging flood scoured everything in its path, leaving a scablike landscape that is unique to the region.
The Colorado Plateau, composed of alternating layers of sandstone and limestone, is centered on the Southwest's Four Corners area, where the states of Utah, Colorado, New Mexico, and Arizona meet. Water erosion is primarily responsible for the region's towering cliffs, many natural bridges and arches, and deep gorges. Eight national parks in southern Utah alone feature landscapes that were formed by water erosion. In northern Arizona, the Colorado River scoured the spectacular Grand Canyon. This gorge, although not the world's largest, certainly ranks among its best-known and most scenic natural attractions.
The Rocky Mountains extend from northern New Mexico to Montana and as a mountain chain northward into Canada and into Alaska. The Rockies actually are a series of mountain ranges, each of which is recognized by a regional name. The highest points in New Mexico, Colorado, Wyoming, Montana, and Idaho are all Rocky Mountain peaks. Colorado alone has 17 peaks that reach an elevation of more than 14,000 feet (4,267 meters). The state's highest peak, 14,433-foot (4,399-meter) Mount Elbert, also is the highest elevation in the American Rockies. Mountain glaciers have scoured the jagged terrain for which the mountains are so famous. Colorado's Rocky Mountain National Park, Grand Teton National Park in Wyoming, and Glacier National Park in Montana all offer marvelous glacier-carved scenery.
Moving eastward from the Rocky Mountains and stretching to the Appalachians is a huge area of lowland plains. The western portion, the Great Plains, lies west of a line that roughly coincides with the 100th meridian and includes portions of Texas, New Mexico, Colorado, Wyoming, North and South Dakota, and Montana. On the western margin (where Denver, Colorado, calls itself the “Mile High City”), they reach an elevation of more than 5,200 feet (1,585 meters). Eastward, the plains drop very gradually in elevation until they reach the Missouri and Mississippi rivers. Generally flat terrain is broken in places by isolated buttes, mesas, and low mountains such as South Dakota's Black Hills, site of America's famous “shrine to democracy,” Mount Rushmore. The highest peak in the Black Hills, 7,242-foot (2,207-meter) Harney Peak, is also the highest point in Northern America east of the Rocky Mountains.
East of the Great Plains and extending across the Mississippi River basin to the foothills of the Appalachians is a region variously called the Central or Interior Lowlands or Plains. The area extends from north-central Texas to the eastern Dakotas and eastward to Ohio and Michigan. The region coincides with America's “breadbasket.” Excellent soils, ample moisture, and large expanses of flat land that allow the use of heavy equipment help make this region one of the world's most productive agricultural areas.
The Appalachians are an ancient system of low mountains that extend from Alabama to New England (and into eastern Canada). From the air, they give the appearance of an accordion-like series of parallel, southwest-northeast–trending ridges and valleys. This unique land form is the result of geologic folding. Millions of years ago, forces that worked from within the earth pushed toward one another, creating a ripplelike landscape. The mountains are relatively low, reaching their highest elevation of 6,684 feet (2,037 meters) atop Mount Mitchell in western North Carolina. Initially, the Appalachians formed a divide between the eastern seaboard and the country's interior. As the land was forced upward, however, ancient rivers scoured narrow east-west–trending valleys called “gaps.” These passageways, such as the famous Cumberland Gap, located at the point where Kentucky, Tennessee, and Virginia meet, created corridors followed by early Amerindians, European pioneers, and, later, railways and highways.
Piedmont and Atlantic and Gulf Coastal Plains
Immediately to the east of the Appalachians is a hilly upland area that gradually drops toward the coastal plain. Its name comes from its location: pied (foot) and mont (mountain). At the point where the Piedmont and the coastal plain join is a narrow strip called the “fall zone” or “fall line.” The name, of course, comes from falls or rapids that occur along streams that flow eastward from the mountains. These areas became important points for early settlement.
Rapidly flowing water provided an ideal site for water-powered saw, flour, and other industrial mills. It also marked the head of navigation on streams that flowed from the mountains to the Atlantic Ocean. Goods being transported by water had to be placed on land-based vehicles (and vice versa) in a process called “break in bulk.” Warehouses often developed around such sites to take advantage of the need for storage. Lively trade and commerce also are associated with such locations. Nearly 30 cities were founded and grew as a result of the many advantages offered by the fall zone (line). They include Philadelphia; Baltimore; Washington, D.C.; Richmond, Virginia; Raleigh, North Carolina; Columbia, South Carolina; Augusta, Georgia; and Tuscaloosa, Alabama.
A low-lying, flat-to-gently-rolling coastal plain extends from New Jersey to Texas. Regionally, it is divided into the Atlantic and Gulf coastal plains. The Atlantic portion extends from the mouth of New York's Hudson River to eastern Florida. The Gulf coastal plain includes an arc that extends from western Florida to southern Texas. Along the coast, thriving urban centers such as Boston, Massachusetts; New York City; Tampa, Florida; and the Galveston Bay area of Texas all developed as seaports. Ample freshwater, fertile soils, woodlands, and access to the sea combined to make this region attractive to early settlers.
CLIMATES AND ECOSYSTEMS
With the exception of Alaska and Hawaii, the United States lies within the easily developed and environmentally less-challenging temperate midlatitudes.
Most of the country expe-riences relatively moderate conditions of weather and climate. With the exception of aridity, nearly all extremes are seasonal rather than lasting yearround. Even where nature imposes a challenge, such as in the arid West, settlers have found ways to make the land bountiful. Water storage and diversion, irrigation, air-conditioning, insulation, and artificial heating are just some of the ways in which Americans are able to adapt to the extremes that exist.
As mentioned previously, the United States is the only country that includes within its territory each of the world's climates and ecosystems. At the extremes are frigid arctic conditions in northern Alaska, the steaming tropics of Hawaii, and the parched deserts of the Southwest. All other climates occur somewhere within the adjoining 48 states. Varied climatic conditions are important for several reasons. First and foremost, climate is the major control of ecosystems. Because of its many climates, the United States has a tremendous diversity of natural vegetation, animal life, soil conditions, and water features. Also, environmental diversity makes any human activity, including all types of farming, possible someplace within the country.
Finally, if there is any truth to the statement “variety is the spice of life,” then Americans are indeed fortunate. A marvelous multitude of environments offers unlimited opportunities for development. Geographers identify, name, and classify climates and ecosystems in many ways. In the section that follows, the author uses descriptive terminology to the degree possible.
The Humid East
East of roughly the 100th meridian, the United States experiences a humid climate. In the Southeast, humid subtropical conditions prevail. Moisture is ample: Most locations receive 40 to 60 inches (100 to 150 centimeters) of precipitation per year and some places get considerably more. The Gulf Coast region, southern Florida, and portions of Appalachia receive 60 to 80 inches (150 to 200 centimeters). Severe drought is infrequent. With an annual average 55 inches (140 centimeters) of precipitation, Louisiana is the nation's wettest state as measured by the statewide average of all recording stations. Moisture falls throughout the year, although a peak occurs during the sum mer months because of convectional thunderstorms. Winters tend to be mild. Freezing temperatures and snow are very rare in Florida and along the Gulf Coast. Temperatures drop and snowfall increases as one moves northward and inland from the moderating influence of the ocean. Summers are long, hot, and sauna-like due to the region's high humidity.
The Northeast experiences a humid continental climate. Ample moisture is received throughout the year, although the total is slightly less than throughout most of the South. Driest conditions occur in the western portion of the region: Much of the Corn Belt receives an average 20 to 40 inches (50 to 100 centimeters) of moisture. Eastward, the amount increases: Coastal and upland areas receive 40 to 60 inches (100 to 150 centimeters) annually. Snowfall is common during winter months and can cover the ground from November through April (or even longer) in some northern areas. Annual amounts in excess of 100 inches (250 centimeters) are not uncommon, particularly in locations that receive “lake effect” snow (winds pick up moisture as they blow across the Great Lakes). Summer temperatures tend to be moderate, but winters can be frigid. Some northern locations have a January temperature average that ranges between 0 and 10°F (?12° to ?18°C). The region does hold one weather-related record: A weather station atop New Hampshire's Mount Washington experienced a sustained surface wind of 231 miles per hour (372 kilometers per hour), the highest straight wind velocity ever recorded on Earth's surface.
Under natural conditions, the eastern half of the United States supported a dense cover of broadleaf, needleleaf, or mixed forests. Today, much of the natural vegetation cover has been cleared for agriculture and other types of land use. In both climate zones, but particularly in the southeastern United States, a considerable amount of land that was once cleared for agriculture is being returned to woodland. Birds, marine life, and mammals large and small abound in the eastern United States. Conservation programs have actually increased many wildlife populations over what they were a century ago. As the country becomes increasingly urbanized, rural populations decline, thereby actually increasing wildlife habitat. Soils vary greatly in quality from place to place. In the far north, they tend to be thin, acidic, and generally poor. Throughout much of the South, soils were destroyed by poor agricultural practices. Corn Belt soils of the Midwest, however, are among the richest in the world.
The Dry Interior West
Most of the country's western interior—an area that extends from the desert Southwest and eastward from the Sierra Nevada and Cascades to approximately the 100th meridian—receives scant moisture. Both high and low temperature extremes are much greater here than in the eastern part of the country. In this region, actual temperature conditions vary depending on latitude and elevation. Most of the area receives less than 20 inches (50 centimeters) of precipitation annually. The desert Southwest, including much of eastern California, Nevada, portions of Utah, the southern half of Arizona and New Mexico, and western Texas, receives less than 10 inches (25 centimeters) of precipitation per year. Nevada is the nation's driest state, with an annual average of 9 inches (23 centimeters) of precipitation, and Las Vegas is the driest city, receiving about 4 inches (10 centimeters) of moisture each year. The distinction of being the nation's driest spot goes to the parched desert floor of Death Valley, California, which receives a scant annual average of 1.4 inches (3.6 centimeters) of rainfall. Despite its extreme aridity, during the very wet spring of 2005, a large lake formed on the valley's floor! Another record goes to Tucson, Arizona. That city holds the distinction of having recorded the world's lowest relative humidity—a bonedry 0.8 percent (statistically 1 percent). Summer is the wettest season, when most rain falls in torrential thunderstorms.
The region's aridity is the result of two primary influences. As prevailing winds blow from west to east across the high mountains, most of their moisture is released on the windward (western) side. As they descend down the leeward (downwind) side of the Sierra Nevada and Cascades, they warm, creating a “rain shadow” effect. East of the western mountains, only scattered mountain peaks catch enough moisture to support forest growth. In the desert Southwest, a second control influences aridity. The region is overlain by a semipermanent high pressure system. If you have seen the face of a barometer, you know that rising (higher) pressure is associated with stable weather conditions. This condition persists throughout most of the year in these drier areas of the country.
Because of its continental location or as a result of its being far removed from the moderating influence of the ocean, the interior West commonly experiences weather extremes. Summers can be fiercely hot and winters frigidly cold. Temperatures have reached a sizzling 135°F (57°C) in California's Death Valley, only one degree below the world's record high registered in the Sahara Desert. Throughout the region, but particularly in the desert Southwest, afternoon temperatures can soar higher than 100°F (40°C) for weeks on end. Low temperatures are a function of latitude and elevation.
Throughout the winter months, the nation's low temperature is often recorded in spots such as Wisdom, Montana; Stanley, Idaho; or even Bellemont, Arizona. Each of these communities is located at a very high elevation. The lowest temperature ever recorded in the 48 coterminous states was a frigid ?70°F (?57°C) at Rogers Pass, Montana.
Before the arrival of Europeans, much of the central interior was covered with a seemingly endless sea of grass. From west to east, shorter steppe grasslands gradually gave way to taller prairie grasses as precipitation amounts increased. This region was home to the American bison (buffalo), an estimated 60 million of which roamed the grassland-covered plains. Within a century, their numbers plummeted to about 1,100 in one of the greatest mass slaughters in history. Other large animals that roam the plains include deer, elk, and antelope. Where water is available for irrigation, soils tend to be quite fertile. Because of the aridity, nutrients have not been leached (washed out).
The Pacific Region
Because it borders the Pacific Ocean, coastal California southward of approximately 40°N latitude experiences a mild and very pleasant Mediterranean climate. In fact, many people believe the Mediterranean to be the world's most pleasant environment. This is one reason why “sunny Southern California” has been a primary magnet for migration for many decades. Summer temperatures rarely reach into the 80s°F (mid-20s°C), and freezing temperatures are unknown in many locations. Severe storms are uncommon. Despite the summer drought and lack of storms, much of the region receives 30 to 50 inches (75 to 125 centimeters) of rainfall annually. Mediter-ranean weather is unique in one major respect — it is the only climate that experiences summer drought. Weeks can pass during the summer months without a cloud appearing in the sky.
Natural vegetation is chaparral scrub and grassland, with many eucalyptus species that were introduced from Australia during the mid-1800s. Native wildlife has largely succumbed to human population growth and destruction of natural habitat. Coastal northern California and the Alaskan panhandle have a soggy West Coast marine climate that is moist and temperate. Compared to locations at comparable latitudes, the region's summer temperatures are considerably cooler and winter temperatures much warmer. Some locations may go years without experiencing snowfall, something unheard of east of the Cascades. The area that lies west of the mountains is the wettest portion of the continental United States. Warm moisturebearing winds that blow in from the Pacific are forced aloft over mountains soon after they reach the coast. Rising air cools, condenses, and is ripe for precipitation. Cities such as Seattle, Washington, can go weeks at a time without sunshine. Because of the constant high humidity and frequent drizzle, it is often jokingly said that residents of the region do not die, they just rust away! The wettest spot in the continental United States is in northwestern Washington's Olympic Peninsula, where up to 150 inches (380 centimeters) of moisture falls each year. Several locations in the Cascades and Sierra Nevada receive several hundred inches of snowfall each winter. The snowfall record belongs to Washington's Mount Baker Ski Area. During the winter of 1998–1999, it was buried beneath an incredible 1,140 inches, or 95 feet (2,896 centimeters, or 29 meters), of snow!
This region is home to some of North America's most remarkable forests. Reliable moisture and high relative humidity, including frequent fog, are ideal for tree growth and fire suppression. Until recent years, when the harvest was sharply reduced as a result of environmental issues, the largely needleleaf evergreen forests of the Pacific Northwest provided most of the country's high-quality lumber. California alone can boast of three enviable world records held by trees growing there. The world's tallest tree is a redwood in an undisclosed (for protection) location in northern California's Redwood National Park. The towering giant, named Hyperion, reaches a height of 379 feet (115.5 meters). The state also lays claim to the world's largest tree by mass. The General Sherman Tree in Sequoia National Park has a volume of 52,500 cubic feet (1,486.6 cubic meters) and a base diameter of 36.5 feet (11.1 meters). “Methuselah,” a nearly 4,800-year-old bristlecone pine located in California's White Mountains, is not only the world's oldest tree, it is believed to be Earth's oldest living thing.
Despite its largely humid tropical climate, Hawaii has an amazing diversity of microclimatic conditions and resulting ecosystems. For a small island, Maui almost certainly holds some kind of environmental record. One can stand in a beautiful Mediterranean-type landscape on the slope of 10,000-foot (3,050-meter) Mount Pu'u' Ula'ula and be within roughly 6 miles (10 kilometers) of nearly all of Earth's ecosystems—from steaming tropical rain forest to water-starved desert and subpolar conditions. Only a polar ice cap condition is missing! An equally amazing extreme exists on the island of Kaua'i. There, one can stand in a desert environment with scant vegetation dominated by grasses, scrub plants, cacti, and irrigated agriculture. Only several miles away, rain falls almost constantly over Mount Waialeale, making it the world's wettest spot with an average 460 inches (168.5 centimeters) of rainfall each year! This anomaly is created by the orographic effect (rain) and rain shadow (aridity).
Much of Alaska experiences short, cool summers and long, often severe winters. Only along the southern coast are temperatures moderate. The capital, Juneau, and largest city, Anchorage, are considerably warmer during the winter months than are many cities in the northern “Lower 48” (as Alaskans refer to the region). Inland, temperatures can plummet to ?78°F (?61°C), but also soar to 100°F (40°C). Moisture is adequate throughout the year, although much of it comes in the form of snow that can fall during any month in some locations. Much of the state supports a taiga (or boreal) forest composed of dense stands of larch, pine, spruce, and aspen. Only in the far north does woodland give way to the tundra. Here, shallow soils and a very short growing season support a stunted ecosystem dominated by mosses, lichens, clump grasses, and hardy flowering plants. Moose, bears (black, brown, including the huge Kodiak and grizzly, and polar), deer, and caribou thrive here. Marine life includes whales, seals, walrus, and much of the seafood (fish and crab) enjoyed by Americans.
Throughout human history, water has attracted human settlement, economic development, and transportation. Whether Amerindian or European, most early settlements developed around reliable sources of freshwater. The significance of water to human settlement is evident when one studies a detailed political or population map. Observe how many major cities border an ocean, a lake, or a river. This importance also is suggested by the hundreds of towns and cities that incorporate some water feature in their name. How many such communities can you identify that include such terms as ocean, lake, river, rapid(s), fall(s), spring(s), well, bay, port, or harbor?
Water is essential in many ways. We all know how important it is in our homes when used for domestic purposes. Agriculture, however, is the nation's chief user of water, followed by industry. Shipping by water is the least-expensive means of transportation by a considerable margin. Mills, built at points where streams cascaded over falls or rapids, were an early source of power for milling grain, sawing lumber, and other industrial uses. Today, their importance has been replaced by huge hydroelectricity-producing dams. Both oceanic and freshwater fishing is an important commercial and recreational activity; people flock by the millions to water for recreational purposes. Along coasts, many of the largest cities grew around a river mouth or natural harbor. In the nation's arid interior, nearly all cities are located at oasis sites.
Water, one can argue, is the resource most essential to life, yet water-related problems loom on the horizon. A growing population, particularly in the water-deficient Southwest, has pushed available water supplies to their limit. Water pollution is a problem in many areas, including the Great Lakes, many smaller water bodies, and rivers in most areas of the country.
Groundwater stores are being polluted in some areas and critically depleted in others.
The United States is the only country bordered by three of the world's oceans—the Pacific, the Atlantic, and the Arctic. (Technically, Russia faces on the Baltic Sea, not the Atlantic Ocean.) This gives the country a tremendous advantage in many ways.
Politically, oceans do not “belong” to anyone; hence, they serve as a buffer against potentially hostile neighbors. Economically, they are the source of countless marine resources, scenic beauty (resulting in increased property values), and shipping access to much of the world. Physically, oceans moderate temperatures and serve as the source of atmospheric moisture. With possible continued warming of Earth's atmosphere, the Arctic Ocean may become a major focal point of global navigation. In the absence of thick sea ice, ships could easily pass between Europe, Asia, and North America.
An estimated 90 percent of the world's natural lakes were formed by glacial action. During the Pleistocene (ice age), glaciers reached into the United States as far south as the Ohio and Missouri rivers and also formed in many of the higher mountain ranges. Most lakes, therefore, are in the northeastern section of the country and north of the Ohio and Missouri rivers. Elsewhere, in the Southeast and the West, most “lakes” are actually reservoirs, water bodies formed behind dams.
The Great Lakes form the world's largest system of freshwater. In fact, Lake Superior is the world's largest freshwater lake by surface area. Water from the Great Lakes reaches the Atlantic Ocean through Canada's St. Lawrence River. For a half century, ships have been able to pass between the Great Lakes and the Atlantic by way of the St. Lawrence Seaway.
The major river system in the United States is that formed by the Mississippi and its two major tributaries, the Ohio and Missouri rivers. This giant network drains about 41 percent of the 48-state area, including all or part of 31 states (and two Canadian provinces). The combined MissouriMississippi River is about 3,700 miles (5,970 kilometers) long, a distance surpassed only by the Nile and Amazon rivers. Barges can navigate the rivers upstream to Minneapolis-St. Paul, Minnesota; Pittsburgh, Pennsylvania; and Sioux City, Iowa. New Orleans, Louisiana, located near the mouth of the Mississippi, was one of the nation's leading seaports before Hurricane Katrina's devastating blow in 2005.
Dependence on a river is illustrated by current problems along the Missouri. Severe drought during the first decade of the twenty-first century has caused the river's flow to reach a critically low level. Recreational use, hydroelectric energy production, barge traffic, and even the domestic water supply of some riverside communities have been severely affected as a result.
Many eastern rivers are of local importance. Certainly the Hudson River has played a very significant role in the growth of New York City. In the Southeast, the Tennessee, Cumberland, and other rivers were transformed by one of the world's most massive reclamation projects. Beginning in 1933, during the Great Depression, the Tennessee Valley Authority (TVA) built nearly 50 dams on this drainage system. Their construction spurred the regional economy by creating jobs for tens of thousands of people in one of the nation's poorest regions. The dams also gave the area a clean and inexpensive source of (hydroelectric) energy, controlled flooding that had long plagued the region, and created reservoirs that provide many recreational opportunities.
In the Southwest, the Rio Grande and Colorado River flow southward across desert landscapes. Both streams are of far greater importance than their relatively small volume of water might suggest. In fact, millions of people, huge cities, and billions of dollars in agricultural production depend on their flow. The Rio Grande flows from the Colorado Rockies, through central New Mexico, and into Texas, where it forms the border between the United States and Mexico. It is dammed in three locations, is vital to regional agriculture, and is often dry along much of its lower course.
The Colorado River is controlled by eight dams and reservoirs, including Glen Canyon Dam and Lake Powell on the Utah-Arizona border and Hoover Dam and Lake Mead just east of Las Vegas, Nevada. Huge water diversion projects have artificially supported the Southwest's booming population and economic growth. Phoenix and Tucson, Arizona, draw water from the Colorado River, as do California's Los Angeles basin, San Diego, and the agriculturally productive Imperial Valley. Las Vegas, the nation's fastest-growing city, also depends on the Colorado for its water supply. Coastal southern California also obtains water from streams that flow from the Sierra Nevada.
With 35 million residents in California and booming populations in Arizona, Nevada, and the upper basin of the Colorado River, many observers wonder how long it will be before the region faces a severe water crisis. Without the current massive diversion of water, the region could support only a small fraction of its present population. What might happen, for example, if the severe drought that has plagued much of the region since 2000 continues and intensifies?
In the Pacific Northwest, the mighty Columbia and its chief tributary, the Snake River, produce huge amounts of hydro-electric energy. They are also the source of water for irrigation and domestic use and for important recreational resources. Alaska's Yukon River is a large stream but is of little economic significance.
Groundwater is water deposits stored in an aquifer, the upper limit of which is the water table. In arid regions, an aquifer may be nonexistent or may lie more than 1,000 feet (300 meters) below the surface, as is the case throughout much of the desert Southwest. Groundwater is tapped by wells, although in some places it reaches the surface through springs. Throughout much of the country, both the quality and the quantity of groundwater deposits are in sharp decline. Aquifers can easily be contaminated by the seepage of pollutants. Fortunately, monitoring systems can determine when they reach a dangerous level. In many areas, groundwater—some of which is many thousands of years old—has taken on a foul taste or odor because of the earthen material in which it is embedded.
Salt and sulfur, for example, can reduce water quality. In many locations, water from aquifers is being used faster than it is being replaced. This is occurring in the vicinity of many cities in the West. In the country's midsection, from South Dakota to the Texas panhandle, much of the agriculture depends on irrigation with water taken from the Ogallala Aquifer. This aquifer is being mined at a rate much greater than its recharge. The future of this region depends on either finding an alternative source of water or on developing an economy that is in balance with available water resources.
Although blessed in many ways by its environmental diversity, the United States is also unique in an unfortunate way: It experiences a greater variety of natural hazards than does any other country and by a wide margin. Earth's atmosphere, lithosphere, hydrosphere, and biosphere all wreak havoc on land and property and often take a toll on human life. Are natural forces always “at fault”? In this context, we must recognize the difference between a natural hazard, something that poses a risk, and a natural disaster, a natural occurrence that inflicts damage on human life or property. Simply stated, people who live in hazard-prone areas elect to do so knowing that they face potential risk. They bet that nature's wrath will not affect them. Some places are much safer or much more dangerous than others. In July 1998, the National Geographic Society published a map entitled Natural Hazards of North America, which shows the distribution of 11 environmental hazards. Amazingly, a very close correlation exists between population concentrations and both environmental hazards and natural disasters!
The most dangerous areas are the Pacific Coast states and the eastern half of the country. Yet these areas are precisely where the great majority of Americans live. Coastal regions, wooded areas, lakeshores, river valleys, and mountains present pleasing visual landscapes to which people flock, making property values soar. In fact, research has shown that the greater the potential environmental risk, the higher the population density and value of property! Ironically, the nation's safest areas—the Great Plains and much of the Great Basin—have the lowest population density, the highest out-migration, and the lowest property values.
The following list presents the nation's 10 worst natural disasters in terms of loss of life. In all instances, figures are estimates, some of which vary greatly:
- 1900 Hurricane (Galveston, Texas) 6,000–12,000
- 1928 Hurricane (Florida Atlantic Coast) 2,500
- 1871 Forest fire (Peshtigo, Wisconsin) 1,200–2,500
- 1889 Flood (Johnstown, Pennsylvania) 2,210
- 1893 Hurricane (coastal Louisiana) 2,000
- 2005 Hurricane (New Orleans and Louisiana and Mississippi coasts) 2,000
- 1893 Hurricane (Sea Islands of South Carolina and Georgia) 1,500
- 1906 Earthquake (San Francisco, California) 500–3,000
- 1925 Tornadoes (Midwest) 727
- 1938 Hurricane (New England) 720
Such figures are quite alarming, but to put them in perspective, the total of the above list is 29,000 deaths. On the other hand, each year the country experiences about 44,000 highway fatalities, 50,000 violent deaths (murder, suicide, etc.), and about 445,000 deaths related to smoking. In addition, it is significant to note that only one of the events has occurred since 1928. Two factors have contributed to the sharp reduction in loss of life. First, forecasting has greatly improved: People can be alerted to many impending events well in advance, thereby allowing them to take necessary precautions. This is particularly true of weather-related hazards such as hurricanes, tornadoes, blizzards, or floods that cause rain or snowmelt.
Once generated, tsunamis (incorrectly called “tidal waves”) also can be forecast. Scientists are even showing some progress in their attempts to predict earthquakes and volcanic eruptions. A second factor involves engineering and site selection. Today, settlements and structures are much more apt to be located and built with safety in mind. Many other steps can be taken. Dams, levees, preservation of wetlands, and reforestation all reduce the threat of flooding. Cellars offer protection from tornadoes, and improved forest and grassland firefighting strategies and technology can reduce losses from such conflagrations.
Atmospheric hazards include hurricanes, tornadoes, heavy flood-causing rain, blizzards, icerelated storms including hail and sleet, lightning, and drought. Hurricanes, responsible for 6 of the country's top 10 natural disasters, are generally limited to the Gulf and Atlantic coastal zones. Although their winds can be destructive, the greatest damage is caused by water. Along coasts, stormpushed surges of water up to 20 feet (6 meters) high can rush ashore, destroying everything in their path. Inland, torrential rains can cause severe flooding. In New Orleans, Hurricane Katrina breached protective levees in several places and dropped up to 15 inches (38 centimeters) of rain. It was the nation's greatest urban disaster since the San Francisco Earthquake of 1906. With damage estimated in excess of $80 billion, it also was the country's most costly natural disaster by a wide margin. Tornadoes, blizzards, hail and ice storms, and flooding are commonplace throughout most of the eastern half of the country. Blizzards, drought, and local flooding pose threats in the Great Plains and much of the interior West.
The Pacific Coast is the most hazard-prone area of the United States. It lies within the Pacific “Ring (or Rim) of Fire,” a zone of geologic instability that encompasses most of Earth's seismic and volcanic activity. From southern California to Alaska's Aleutian Islands, the Pacific and North American plates slide, crunch, and grind against one another, creating one of Earth's most earthquake-prone zones. Anchorage, Seattle, San Francisco, and Los Angeles all sprawl across active geologic faults and thus are in constant peril. Volcanoes dot the landscape from the Cascades northward into Alaska and, of course, in Hawaii. Many are active. In 1980, Washington's Mount St. Helens erupted violently. The blast devastated the surrounding area for many miles and caused 57 deaths. Geologists had anticipated the explosion, and the peak is quite isolated, factors that contributed to minimal property destruction and loss of human life. In addition, the Pacific Coast is subject to earth creep and landslides, raging wildfires, and periodic droughts.