Lecture – 8 geography of the usa

Alaska and Hawaii
Alaska, whose area is equal to one-sixth of the area of the lower 48 states, consists of mountain ranges curving concentrically around the Gulf of Alaska and extending west in an are forming the ALEUTIAN ISLANDS. North American’s highest point, mount MCKINLEY (6,194M), in the Alaska Range. North of these mountains is a broad plateau bisected by the Yukon River. North of it is the BROOKS RANGE, the northern base of which slopes to the Arctic Ocean, including the oil-rich PRUDHOE BAY area.
Hawaii, the 50^th state, located near the center of the Pacific Ocean, consists of volcanic islands aligned in a northwesterly direction. The volcanism is older and the islands are lower northwestward. Either the ocean crust is moving northwest across a hot spot, or the hot spot is moving southeast under the crust. Active volcanoes, KILAUEA and MAUNALOA, are located on Hawaii, the southeastern most islands.
Inland water covers about 200,000sq km, or almost 2 percent of the total area of the United States. The MISSISSIPPI RIVER, flowing south across the eastern half of the conterminous United States, is major both in length (3,779km) and annual discharge (18,200cu m per sec). by contrast, the COLORADO RIVERS (Colorado) is about one-third as long as the Mississippi River system, but its average annual discharge is only 2 percent as great. An area the Atlantic seaboard, only slightly larger than the Colorado river basin, has 20 rivers- including the CONNECTICUT RIVER, DELAWARE RIVER, HUDSON RIVER, and SUSQUEHANNA RIVER –each only one-third as long as the Colorado but together discharging 20times as much as the Colorado.
In terms of discharge, the major rivers, in addition to the Mississippi, are the SAINT LAWRENCE RIVER, OHIO RIVER, MISSOURI RIVER, COLUMBIA RIVER and SNAKE RIVER. The YUKON RIVER is Alaska’s principal river. Where annual precipitation averages lass than mm, ever mail streams are mostly ephemeral, flowing only when there are wet seasons or local storms. Water supplies in those areas, to a considerable degree, must be obtained from groundwater, and in parts of the arid southwestern states withdrawals (mostly for irrigation) have caused groundwater levels to fall alarmingly in places, enough to cause localized subsidence of the land surface and even damage to buildings.
Lakes and peat bogs are numerous in the glaciated parts of the United States, especially in northern Minnesota .The lakes are small and used primarily for recreation, but the GREAT LAKES are important arteries of transportation. Florida has lakes and bogs at limestone sinks,
Including Lake OKEECHOBEE. The troughs of the Great Basin have ephemeral lakes. A few permanent once are located at the eastern foot of the Sierra Nevada. The Salton Sea and Great Salt Lake are saline. Many of the, especially in the west, have been created by dams; Lake MEAD has the greatest capacity.