Julia Perkins, age 12, of Providence, R.I., for her question:
HOW ARE VALLEYS FORMED?
Most valleys on dry land are formed by the running water of streams and rivers, and by the erosion of slopes leading to them. Erosion moves material down the slopes to the valley floor where the stream carries it to a lake or to the ocean. In addition, the stream may erode its channel deeper.
A valley may also be formed when a long, narrow section of the earth's crust sinks below the surrounding area. A valley formed in this way is called a rift valley. One system of rift valleys extends about 4,000 miles from the Sea of Galilee south through the Red Sea and into southeastern Africa.
Glaciated valleys are valleys that were enlarged by the action of glaciers. These valleys are often formed high in mountains. They are U shaped rather than V shaped.
A valley is a natural trough in the earth's surface. Systems of valleys extend through plains, hills and mountains. Streams and rivers flowing through valleys drain interior land regions to the ocean. Many valleys have fertile soil and make excellent farmland.
All valleys are actually similar in shape. The bottom of a valley is called its floor. The floor usually slopes gradually in one general direction. Mountain valleys usually have narrow floors but in low lying plains: a valley floor may be several miles wide.
Various kinds of valleys are named according to their appearance. A deep valley with steep walls is called a canyon. One of the most famous canyons is Grand Canyon in Arizona.
Along coastlines, valleys that are flooded by the ocean are called drowned valleys.
Chesapeake Bay and Delaware Bay are drowned valleys.
Many deep submarine canyons are found on the slopes leading up from the ocean floor to the edge of the continental shelf. Hudson Canyon is a submarine canyon.
The part of the valley floor along river banks is called the flood plain. The flood plain is part of the river channel, but it is used only during a flood. Buildings on it may be damaged when the river floods.
The sides of a valley are called valley walls or valley slopes. The ridge formed where the wails of neighboring valleys meet is called a divide.
Where a valley joins a larger valley from the side, the two floors usually meet at the same level. But sometimes the floor of the side valley is higher than the floor of the main valley where they join. The side valley is then called a hanging valley. A river flowing through a hanging valley may form a waterfall where the water enters the main valley.
One of the most famous valleys in the world is the Valley of Kings. It is a rocky, narrow gorge which was used as a cemetery by the kings of ancient Egypt between 1550 and 1200 B.C. The Valley of the Kings is sometimes called the Valley of the Tombs of the Kings. It lies on the west bank of the Nile River at Thebes. Sixty two tombs have been discovered in the Valley.