Strong seasonal winds in South Asia and other areas in the tropics and sub-tropics. In the summer, the southwest monsoon blows warm, moist air from sea to land, bringing heavy rain. The torrential storms can last several months and are vital to agriculture. In the winter, the northeast monsoon blows cold, dry air from the central Asian mountains to the sea, bringing dry, dusty conditions to India and neighboring lands. Monsoon-like rains also occur in northeast Australia, East Africa, and the southern United States.
A dry, barren region that receives little or no Precipitation, usually less than 10 inches (25 cm) per year. A desert can be hot or cold. Without many plants to hold the soil with their roots, the Wind can blow away topsoil and scour the landscape into fantastic shapes. Sand that catches on vegetation can form Dunes. The largest hot deserts in the world lie near Latitudes 30° South and 30° North, where descending high-pressure air masses push out the low-pressure air masses that bring moisture. Temperatures in the desert can range from over 100° F (38° C) during the day to below freezing at night. The largest hot desert is Africa’s Sahara, with 3.5 million square miles (9 million square km). Antarctica is a desert even though it’s cold and covered with ice. Its annual Precipitation is less than 4 inches (10 cm) of rain, making it one of the world’s driest areas. Atacama desert in northwestern Chile is the driest place on earth. Parts of it haven’t had Rain in over 400 years.
A rugged mass of rock that rises above the surrounding landscape. Volcanic Mountains, like Africa’s Mount Kilimanjaro, form when Lava pours out of a Volcano’s vent, forming a cone shape around the opening. Mountains also occur where Tectonic Plates move together or apart and Magma rises to the earth’s surface. Fold mountains, like the Himalayas, form when two Tectonic Plates push against one another, crumpling the earth’s crust. Fault-block mountains, like the Sierra Nevada in California, are huge blocks thrust up or down along Fault lines. Dome mountains, like the Black Hills in South Dakota, are bulges of land pushed up from below by Magma. Mountains are being built up and eroded away all the time. The Appalachians in the eastern United States are ancient fold mountains well worn by Erosion. Nine of the ten tallest mountains in the world (on land) are in the Himalayas. The largest mountains on earth are under the Oceans. The tallest mountain we know about, 10 miles (16 km) high, is Olympus Mons on Mars. The Andes in South America form the world’s longest continuous mountain chain.
A mound or ridge of coral polyps and their hard limestone remains, combined with sand and minerals. Coral reef Biomes occur only in shallow, warm waters, mostly in the Pacific and Indian Oceans. A coral reef provides a rocky shelter for a wide variety of sea life, but the reef itself is fragile and grows very slowly. Coral reefs include fringing reefs, which hug the rocky shelves extending from shores of Islands or Continents; barrier reefs, which are separated from the land by a Lagoon; and Atolls, which are ring-shaped Islands. The Great Barrier Reef in northeastern Australia is the world’s largest system of coral reefs, stretching 1,250 miles (2,011 km) along the Queensland coast. El Capitan, the highest mountain in Texas, is made up of fossilized coral reefs.
Low evergreen scrub vegetation. These dense thickets of drought-resistant trees and shrubs can regrow quickly after seasonal fires. Chaparral is also the name for the Biome where these plants are common. It has a hot, dry summer and wet, mild winter. Although there is little or no Rain in the summer, too much Precipitation in the winter washes nutrients from the rocky, thin soil. Chaparral is often found between other Biomes like Desert (drier) and Grassland (wetter). Chaparral occurs in coastal California and Chile, the Mediterranean, South Africa, and southwestern Australia.
A long gentle curve in the shoreline of an open coast, or the Bay formed by this curve. The Great Australian Bight, on the south coast, stretches for several hundred miles from Eyre Peninsula to the Archipelago of the Recherche. The protruding Delta of West Africa’s Niger River is flanked by the Bight of Benin and the Bight of Biafra.
A very dense tropical Forest of evergreen trees and a great variety of other plants and animals. Rainforests only occur in regions where temperatures and humidity are high and rain is very heavy, at least 80 inches (203 cm), per year. There is little undergrowth except along River banks, because the dense tree canopy blocks almost all the sunlight. Most of the wildlife lives in the canopy, including monkeys, sloths, snakes, frogs, birds, and insects. A rainforest is a very efficient Ecosystem, where microorganisms quickly break down organic matter into nutrients that the trees and plants rapidly absorb. Rainforests cover less than 10 percent of the earth’s surface, but contain over 40 percent of all plant and animal species. If the present destruction of rainforests continues, some scientists estimate that at least one-fifth of the earth’s species will disappear within 30 years. Cutting down the rainforest affects Climate. Rainfall in deforested parts of Panama has decreased by 20 inches (50 cm) in the past half century. In 1994 scientists in a remote Australian rainforest found a species of pine thought to have died out millions of years ago. The largest flower in the world, the rafflesia, grows 3 feet (1 m) in diameter–only in the rainforest. The largest expanses of tropical rainforest are in Central and South America, covering a total of 1,370 million acres (5,544,212 sq km).
A tropical coastal Wetland with thick growths of trees in a sheltered saltwater Swamp. The trees that grow in these habitats are also called mangroves. They get rid of salt through glands on their leaves. Some types have stilt-like roots that support the tree above flooding Tides or take in oxygen from the air. Mangrove seedlings can float long distances until taking root in a suitable spot. Mangroves in Ecuador, Thailand, and Malaysia grow as high as 148 feet (45 m). Mangrove forests protect coastlines from Erosion caused by Tides and storms, but people cut them down for wood or drain them for land. Snakes, shellfish, many species of birds, and lots of other animals live in mangrove Swamps. Oysters, snails, and anemones cling to mangrove roots. One unusual fish called the mudskipper uses its fins to skitter across the mud and up the roots. There are about 58,000 square miles (150,220 square kilometers) of mangrove Swamps in the Americas, Asia, Africa, and Australia. Rare West Indian manatees, also called sea cows, live in the mangrove Swamps of Mexico’s Usumacinta Delta.
Tropic of Capricorn
The Tropic of Capricorn lies at 23.5 degrees south of the Equator. In December the sun is directly over the Tropic of Capricorn. This imaginary line passes through Australia, Botswana, Madagascar, Brazil, and Argentina.
An open Grassland with widely spaced trees in a hot, seasonally dry Climate. The largest savannas are found in Africa, South America, Australia, India, and Madagascar. Before large numbers of people settled the American Midwest, savannas were common in Kentucky, Illinois, Missouri, and other states.
A large hollow in the land filled with fresh or salt water. A lake is bigger than a Pond and smaller than a Sea. Lakes can be gouged out by Glaciers (the North American Great Lakes, the English Lake District). They can form when water fills up the Crater of an extinct volcano (Crater Lake, Oregon). And they can form when part of the earth’s crust drops and collects water (Lake Tanganyika in Africa). Lakes die when they fill up with sediment, fill up with vegetation and become Swamps, or dry up faster than Streams can fill them up. The deepest Freshwater lake in the world, Lake Baikal in Siberia, is over a mile deep (1.7 km) in some spots. Canada has more lakes than any other country. Lake Eyre in Australia covers 5,530 square miles (14,323 sq km) when flooded, but most of the year it’s a dry lakebed because the water evaporates away in the Desert heat.