Minh Ngoc Le, age 12, of Lancaster, Penn., for her question:
WHY DOES IT GET COLDER AS YOU GO UP A MOUNTAIN?
It would almost seem logical that as you went up a mountain, an got closer to the sun, you would find that temperatures went up. But this isn't the case. As you go up, the temperatures drop. Altitudesare responsible for this drop.
As altitudes go up, temperatures usually go down. The temperature usually drops about three degrees Fahrenheit for every 1,000 foot increase in altitude, up to an altitude of five to 10 miles. Mount Everest, the world's highest mountain, has an altitude of 29,028 feet above sea level. It is always snow covered and freezingon the upper slopes.
Geologists and geographers define a mountainous area as one that lies at least 2,000 feet above its surrounds. Its land surface is made up of long slopes, deep canyons or valleys and high, narrow ridges. The region also must include two or more zones of climate and plant life.
About one fifth of the earth's surface is covered by mountains. Some continents, such as Australia and Africa, have only a few mountains. Others, such as Asia, have vast areas that are rugged and high. Permanent snow and ice fields cover most of the earth's high mountains. The lower edge of a permanent snow field on a mountain's upper slopes is called the snow line. But this line's location often depends on the height of the sun, the strength of winds, the area's temperature and its moisture.
The snow line on the same mountain range may change from year to year. In the tropics, the snow line is about three miles above sea level while in the Rocky Mountains, the snow line falls at about two miles above sea level.
In the Alps, the snow line is about a mile and three quarters above sea level and less than one half mile above sea level in Greenland. It is at sea level in polar regions. Mountainous areas were created by movements of the earth's crust. These movements happened very slowly, but on a large scale. Different parts of the earth's crust act in different ways to these movements and as a result form four basic types of mountains.
In some places, the crust folds into great waves. The folded mountains in the Jura range on the French Swiss border are an example. Faultblock or block mountains developed when the earth's crust moved up or down. An example is the Sierra Nevada range in California. Sometimes the crust rose to form domes. The Black Hills of South
Dakota are in this class. A fourth type of mountains are those caused by lava or molten rock. The Cascade Mountains of Washington and Oregon are in this volcanic mountain class.