GEOGRAPHY CHAPTER 2 WEATHERING Compared to the Appalachian Mountains of the Eastern United States, the Colorado Rockies are a brand-spanking-new mountain range. While it might seem strange to think of non-living things such as huge mountains as having an age, this is a big part of what geologists try to figure out: When did the earth s present-day mountains, volcanoes and canyons form? One way geologists can decipher the age of mountains is by using their knowledge of the natural process known as weathering. The breaking down of rock on the earth s surface into small pieces is known as weathering. By comparing the smoothed, rounded slopes of the Appalachian Mountains to the sharp, jagged peaks of the Rockies, geologists can tell that the Appalachian Mountains have undergone much more weathering, and are therefore much older. There are two main types of weathering: mechanical and chemical. Mechanical weathering is a natural process that physically weakens rocks and will often actually break rock into small stones and dust particles. This process happens because water in cracks freezes, and thus expands, splitting the rock. The roots of trees and plants might also grow between cracks and rocks, splitting them into smaller pieces. Chemical weathering is a more dramatic type of weathering. This process actually changes the chemical makeup of rocks, turning it into something entirely new and different. An example of chemical weathering is when carbon dioxide combines with water to make carbonic acid. This solution eats into limestone and dissolves it forming caves. This can occur naturally, yet it also happens as a result of our heavy use of chemicals and fossil fuels.
Acid rain is a huge cause of chemical weathering. When we burn coal to heat our homes, among other things, we release unsafe amounts of sulfur into the air, which pollutes our atmosphere and then returns to the earth s surface in the form of acid rain. In addition to eating away at rocks; acid rain pollutes the earth s rivers, lakes, streams and forests; killing wildlife and causing serious health problems for humans. Click on this website to find out more about acid rain: http://www.epa.gov/acidrain/ardhome.html Effects of Acid Rain http://www.epa.gov/acidrain/effects/envben.html EROSION The process that moves weathered materials (gravel, soil, and sand) is known as erosion. Often, we hear people talk about how soil erosion is a huge environmental problem, caused by people cutting down forests so that they may have more land for farming and livestock grazing areas. While this type of erosion is something we need to be very concerned about, there are also natural occurrences of erosion that are beneficial to maintaining the delicate balance of the earth s cycles. This type of erosion is part of the process of mechanical weathering, which helps to break down hard rock into soil so that plants may grow. Erosion carries weathered materials, like sand and soil, from one place to another. The three most common causes of erosion are water, wind and glaciers. Fast-moving water, after a number of years, will wear away, or erode, rock to form deep canyons, the most dramatic of which is the Grand Canyon in Arizona (pictured at left). This happens because the water carries sediment (small particles of soil, sand, and gravel) which scrapes away at the rock like sandpaper.
Wind causes erosion in places where the climate is very dry and the soil loose - - like deserts and plains areas. Although this type of erosion has been devastating for farmland, as it was during the dust bowl crisis of the 1930s in the Great Plains of the U.S., it also has some benefits. Farmers around the world use the porous particles of loess to hydrate their soil. Loess are mineral-rich deposits of dust and silt, which might be blown thousands of miles by the wind, since its particles are so fine. Glaciers are another major cause of erosion and are remnants of ancient Ice Ages. While its crazy to think about what our immediate environments would be like if they were covered in ice and snow, this is actually the state they have been in for much of earth s history. Geologists estimate that during the past 600 million years, there have been at least four Ice Ages. Right now, actually, we are merely experiencing one of those somewhat rare periods between Ice Ages where the earth s climate is warm enough to allow life to flourish. During these Ice Ages, one third of the earth s water was frozen into these huge, floating pieces of ice known as glaciers. During the periods in between Ice Ages when the planet has warmed up, many glaciers melted and left ridge like piles of rock and debris called moraines. Long Island is, in fact, just one big moraine (no offense to you New Yorkers out there). Unlike the wind and water causes of erosion, glaciers are not agents of weathering. To learn about the damage erosion does to the environment, check out this website: http://www.igc.org/wri/trends/soilloss.html * * * For help with Day 2 s VOCABULARY REVIEW, refer to Chapter 1 s STUDY GUIDE * * *
CLIMATE AND WEATHER While a place s climate gives us a broad generalization about conditions, a place s weather tells us a specific detail about reality. The climate of an area describes the typical weather patterns that place usually experiences over a long period of time. Weather, on the other hand, is what happens in one place over a short period of time in the bottom layer of the earth s atmosphere. Whereas the climate of Florida is fairly hot and humid, the actual weather might bring about a blizzard in July. Who knows? [Well, maybe not. But El Nino and global warming have been known to do some pretty bizarre things to the weather. More about that later.] A place s climate is largely determined by its position on the globe and therefore how much direct sunlight it gets. The amount of precipitation an area receives and how close it is to large bodies of water (like oceans and lakes) also affects a region s climate. Regions that lie within the interior of continents, somewhat distant from oceans, have continental climates. These areas, such as Central Europe, much of North America, and parts of China, experience what we usually think of as normal seasons: hot summers and cold, snowy winters. Although climate conditions are always changing, most geographers agree that the world can be classified into six broad climate regions. These climate categories are: Tropical, Dry, Moderate, Continental, Polar and Highland. Distinctions between these classifications are mainly based on differences of seasonal temperature and average precipitation. If you were to travel north to south in the United States along the 80 degree West line of longitude, you would cross a humid continental climate region and then a humid subtropical climate region. Because of its extreme location, the entire continent of Antarctica has only two climate regions. There are three types of precipitation: convectional, orographic and frontal. Convectional precipitation occurs mainly along the Equator and in the tropics, which are home to much of the world s spectacular rain forests. Orographic precipitation is common where there are coastal mountains, like in Northern California. Frontal precipitation is the most
common. It occurs when two large air masses, or fronts, that are of different temperatures meet. Some parts of the world receive more precipitation then others. Jakarta, Indonesia for example, gets more rain than then Lima, Peru or Cairo, Egypt. THE SUN S EFFECT ON CLIMATE When the United States and Europe are experiencing the snow and sleet of winter, Australians are enjoying the long, hot days of summer. So if you re in Alice Springs, Australia in July, you should expect it to be cooler than it would be in December. So, why is it that the Northern and Southern hemispheres have completely opposite seasons at the same time? The answer has to do with the fact that the earth rotates on an axis which is tilted at an angle of 23½ towards or away from the sun. The time it takes the earth to complete one full turn on its axis is known as a rotation. One rotation takes 24 hours - - one day. A revolution is not only a way to change the world (according to John Lennon), but also the amount of time it takes the earth to completely orbit the sun. One revolution takes about 365 days - - - one year. Only half of the earth can receive the direct light of the sun at any one time. And those two spots which receive the most direct sunlight, the Tropic of Cancer and the Tropic of Capricorn, do so because their latitudes (23½ N and 23½ S, respectively) correspond with this angle of tilt. When the sun appears directly over the Tropic of Cancer on June 21 it is the start of summer, known as the Summer Solstice. The beginning of winter is marked by the Winter Solstice, which occurs when the sun appears directly overhead the Tropic of Capricorn on December 21. The Spring and Fall Equinoxes mark the start of these two seasons, when the sun appears directly overhead the Equator. The sun s heat, however, does not just settle at these spots where it directly hits the earth. Rather, heat from the sun is distributed throughout the world by a process known as convection. The earth s atmosphere works to prevent the moving heat from escaping too quickly. Convection takes place in both the air and water. In the air, winds help to move the heat, and in the
water, the distribution of heat takes place because of currents. The very light winds which serve to move heat at the low latitudes around the Equator are known as the doldrums. [Wouldn t you think they d actually be happy to get a cool breeze now and then around there?] The earth s winds originate from the Equator, and then blow either north or south. Because the earth is tilted, these winds don t blow in a straight line. This phenomenon, known as the Coriolis effect, causes the winds of the Northern Hemisphere to curve to the right, and those of the Southern Hemisphere to bend left. The surface ocean current off the east coast of the United States flows northeast or clockwise. The surface ocean current off the west coast of the lower United States and Mexico flows south or counterclockwise. VEGETATION REGIONS It is pretty common today to hear people talk about the need to save and protect the environment. But what, exactly, does the word environment mean? The environment is usually thought to be anything and everything that we see when we step outside, into the natural world: forests, oceans, birds, bears, insects, trees and plants. Some people might also think of the environment as a community that consists of all of the earth s interconnected species: the animals (humans included), the air, the water, and the land. For the purposes of geography, we define environment, here in this particular context, as the physical conditions of the natural surroundings. This includes such conditions as temperature, precipitation, elevation and type of landforms. Plants that live in the same environment and our interdependent are known as a plant community. What we might think of as a habitat or ecosystem - - - a region in which the environment, plants, and animal life are suited to one another (and clearly interdependent) - - - we call a biome. In addition to looking at politics and climates, geographers also classify regions according to their natural vegetation. The four general types of vegetation regions are forest, grassland, desert, and tundra.
As there are many different types of climates, there are also many different types of forest. Because they are so threatened, the tropical rain forest is probably the most well-known kind of forest. Humans are destroying at a rate too fast for the trees to replenish themselves. The climate of the mid-latitude areas (eastern North America, Europe and eastern Asia) is temperate and has adequate rainfall. In this climate, deciduous forests flourish. Deciduous trees shed their leaves during winter and re-grow them in the spring. In the colder parts of these areas, coniferous forests are more prevalent. Coniferous trees have cones which protect and carry their seeds. These trees are also known as evergreens, because they never shed their leaves, or needles. Chaparral forests harbor a special type of evergreens which are small and accompanied by low bushes. These forests are unique to places with a Mediterranean climate. The central regions of several continents are covered by grasslands. Tropical grasslands, known as savannas, grow in hot climates near the Equator. Temperate grasslands are what is found in the United States, central Asia and Northern Eurasia. These grasslands are known as prairies. The Great Plains of the United States were once an example of this, but intensive farming has plowed the natural vegetation to death. Desert vegetation has adapted to survive the hot, dry climate that makes conditions so inhospitable to humans. The cactus is well known for their unique ability to store gallons of water for lengths at a time. Another tough climate is known as the tundra region. The tundra is found in the coldest parts of the world, around the North and South Poles. The tundra is mostly found north of the Arctic Circle. Because of the constant cold temperatures, only specialized types of plants can grow. These plants have adapted themselves to the short growing season and the permanently frozen layer of soil just below the earth s surface known as permafrost. Certain tundra regions are at such a high elevation that they are considered to be above the tree line: this means that no trees are able to grow there; small plants and wildflowers are the only vegetation.