Earth science fundamentals and applications

Weather and Caves

Windward and Leeward Sides of Mountains- Orographic precipitation, or a rain shadow effect, is an explanation of why the windward side of a mountain is typically rainy and the leeward side dry. The diagram shows that warm moist wind rises, cools and condenses, forming precipitation, which is then lost and the resulting clouds are dry on the opposite side of the mountain. The condition exists because warm moist air rises. As it rises, the decrease in atmospheric pressure (with increased altitude) causes the air to expand and reach dew point. At this dew point, moisture condenses onto the mountain, dumping rain, snow, etc. On the windward side. Then as the air descends on the leeward side, there is little moisture left. This, in combination with the air getting warmer because of compression, creates an arid region (Mountain Weather, 2011).

The actual process of this air mass moving from low to higher elevation, orographic lift, can actually raise the relative humidity in the clouds to 100% and induce precipitation. Orographic fog is sometimes also formed as the air rises up the slope. Depending on the shape of the mountain, where there is high wind, a banner cloud is formed downwind of the upper slopes of mountains that are isolated and very sleep (Alps, Himalayas, some of the Rockies, etc.). This type of cloud is created by the various vortices and local uplifting of the air in relation to the terrain, the most famous being the leeward side of the Matterhorn. In contrast, on the leeward side of the mountain, the warmer air flowing downward is called a foehn wind. Any suspended moisture quickly evaporates as the air descends, and there is a rather distinct cut-off line that tends to form along and parallel to the ridge line on the mountain range, often called the foehn wall. Lenticular clouds are stationary clouds that form downwind of mountains by leeward air, often shaped like lenses (see picture). Additionally, and most well-known in California during certain seasons, a Chinook wave and wind forms above the mountain range and pushes warm air rapidly off the leeward side into the resulting valley or plain (Clouds and Currents, 2010).

Part 2 -- Inquiry Strategy on Cave Formation - A cave, or cavern, is a natural underground space, and may include rock shelters, sea caves, and grottos. Caves are formed by a process called spelogenisis and by various geological processes: chemical erosion, water erosion, tectonic forces, microorganisms, pressure, atmospheric influences, and even digging. However, most caves of any size are formed in limestone by dissolution. Dissolution is the process in which is, essentially, a chemical way of dissolving rock through water or other moisture until a cave is formed. Obviously, some rock and mineral types lend themselves to becoming caves more readily, and are usually comprised of softer material that reacts to outside influences in a more rapid manner. There are, however, a number of types of caves that are formed through different processes (even volcanic action). A new theory says that some caves (about 5%) are caused through the action of sulfuric acid produced by microbial life. In this theory, microbes consume materials, oils, etc. And release hydrogen sulfide gas, which then in turn rises through rocks and combines with groundwater to produce sulfuric acid, which then eats away at the surrounding rock and mineral deposits (Cave Formation, 2002).

Guided Inquiry Method on Caves-

Overview

Teacher

Student

What are caves? How are they formed?

Brief PowerPoint or video on cave formation.

http://www.teachersdomain.org/resource / ess05.sci.ess.earthsys.cavebiogeo/

Ask: How are caves formed? What are different processes? What kinds of processes act together to form caves? Why are caves near volcanos different than caves near limestone mountains?

Experiment

List all the facts learned about caves. Visit some of the cave websites available to show different formations. Divide students into groups of four; give each group 6 ounces of clay and 12 sugar cubes. The clay represents sandstone (harder rock) the sugar, limestone. Put newspaper on the desk and mold the clay around the sugar cube, leaving some of the sugar exposed. Let the "cave" dry for several days, and then soak in water. The sugar will dissolve.