Rivers, lakes, and bays

The United States has many thousands of streams. The longest is the Mississippi. One of its folk names is "father of waters".

Two of the Mississippi's branches, the Ohio River and the Missouri River, also rank among the most important rivers of the world.

Where the Missouri pours into the Mississippi from the west, it colors the river deep brown. Farther downstream, where the clear waters of the principal eastern tributary, the Ohio, join the Mississippi, the difference between the dry west and rainy east becomes apparent. For kilometers, the waters of the two rivers flow on side by side, without mixing. Those from the west are brown with small pieces of soil. The waters from the east are clear and blue; they come from hills and valleys where plentiful forest and plant cover has kept the soil from being washed away.

The long Rio Grande (3,200 km) forms most of the border between the United States and Mexico.

In the northwest, the Columbia River and its chief branch, the Snake River, drain parts of Idaho, Washington, and Oregon. The Sacramento River and its chief branch, the San Joaquin, drain the great valley of central and northern California. The Colorado River and its many branches drain much of southwestern United States. These three river systems have great value as sources of water power.

The Yukon is a river as long as the Rio Grande but considerably greater in volume. It rises in the Canadian Rockies, but in its lower course it flows westward across Alaska to its mouth in Bering Sea.

The United States has thousands of lakes of all kinds and sizes. The northern state of Minnesota, for example, is known as the land of 10,000 lakes.

The Great Lakes make up the largest group of lakes in the country, as well as the greatest collection of fresh-water lakes in the world. Only Lake Michigan lies entirely inside the United States. The Superior, Huron, Erie, and Ontario form a border between north-eastern United States and Canada. They stretch 1600 km from east to west. This is nearly half the distance across the country. The lakes contain about half of the world’s fresh water.

The St. Lawrence Seaway, which the U.S. shares with Canada, connects the Great Lakes with the Atlantic Ocean allowing seagoing vessels to travel 3,861 kilometers inland, as far as Duluth, Minnesota, during the spring, summer and fall shipping season.

Another region of many lakes lies along the Gulf of Mexico and the Atlantic shore. There are hundreds of small lakes and lagoons deep in dark coastal swamps, or protected behind sandy coastal dunes.

A fourth group of lakes lies west of the Rocky Mountains. Some of these lakes are high in the mountains, others are shallow sheets of salty water. The most famous of these salty lakes are the Great Salt Lake, in Utah, and the Salton Sea, which lies about 72 m below sea level in Southern California.

Great bays cut deeply into parts of the United States coast line. There is an almost continuous series of bays along the Atlantic Coast. Many of the deep inlets form excellent harbors. Some of the country's most important ports lie near the heads of these bays. These ports include Boston, New York City, Philadelphia, Baltimore and Newfolk.

The South Atlantic and Gulf coasts have fewer bays. The most important ports here are Charleston, Tampa, Mobile, Galveston and Corpus Christi. Here the harbors are deep enough for ocean-going vessels. The southern coasts also have important coastal river ports, which include Savannah, Jacksonville, New Orleans, and Houston on the Houston Ship Canal.

The Pacific Coast has the fewest bays of any part of the United States coast line. The City of Los Angeles has built an artificial bay to form a harbor for its ocean trade.

CLIMATE

The USA is a land of physical contrasts, including the weather. The southern parts of Florida, Texas, California, and the entire state of Hawaii, have warm temperatures year round; most of the United States is in the temperate zone with four distinct seasons and varying numbers of hot and cold days each season, while the northern tier of states and Alaska have extremely cold winters. The United States has many kinds of climates. The weather ranges from the warm, wet conditions of the Appalachian Highland to the desert conditions of some of the western states. It varies from almost winterless climates in southern Arizona and southern Florida to long, very cold winters in the Dakotas and Montana.

The climate along the northern part of the Atlantic coast is similar to that of England. But in the north central part of the country, summer and winter are worlds apart. There the average difference between July and January is 36 degrees centigrade and more violent extremes are common. The coldest days of a typical January may be 40 degrees centigrade, and the hottest July day may be 45 degrees. This is the sort of climate that is also found in central Asia, far from the moderating influence of the oceans. In the eastern part of the United States, the difference between summer and winter is also very distinct, but not nearly so extreme.

The variations in temperature within the United States have had a marked effect on the country's economy and living standards. There is a long crop-growing season along the south - but in the north it last as long as three months.

West of the Rocky Mountains, running all the way from the Canadian border to Mexico, there are vast areas where almost no trees grow. In this section of the country are the deserts which receive as little as 12.7 centimeters of rainfall a year. Yet, west of the Sierra Nevada Mountains, there are places in which 250 centimeters of rain falls annually.

Although the state of Hawaii is located in the tropical zone, its climate is comfortable because of the ocean currents that pass its shores and the winds that blow across the land from the northeast. The temperature usually remains close to the annual average of 24 degrees centigrade.

Дата добавления: 2015-11-14