Stalactites and Stalagmites THE HYDROSPERE The hydrosphere involves a very complex cycle of water. A few aspects of the cycle are as follows: Runoff Zone of Aeration The Water Table Artesian Wells Geysers Stalactites and Stalagmites

WATER CYCLE

RUNOFF Almost 40 percent of the water that falls on land flows back to the sea by way of surface or underground streams. This water which flows on the surface and in rivers and streams is called runoff. There are several factors which affect the runoff. The first factor is rainfall. Rainfall in itself is affected by several factors. Rainfall not only depends on the amount of moisture, but also the rate of precipitation and the temperature. If there is snow or gentle rains, there will be more evaporation and absorption of the moisture than runoff. Heavy rains can cause rapid runoff. Warm temperatures increase evaporation and cooler temperatures encourage runoff. Gradient is another important factor in determining the rate of runoff. Steep hills or slopes promotes runoff where as gentle slopes or flat areas allow the water to evaporate or pass into the ground water zone. The third factor affecting runoff is the type of rock on which the rainfalls. If the rock is porous, the water is able to sink into the ground. Vegetation is also important in determining whether runoff occurs or absorption of water occurs. How important do you think vegetation is to the amount of runoff? Why?

ZONE OF AERATION The zone of aeration is the upper rock layer through which water can trickle easily. Rainwater does not usually remain in this zone but continues its path downward. Rock openings have air except when it rains; it is this presence of air that gives the zone its name aeration.

THE WATER TABLE The ground water zone or zone of saturation is right below the zone of aeration. The top surface of the ground water is referred to as the water table. The bottom of this zone is usually a layer of rock which has no openings. The depth of the water table varies because of the amount of rainfall. Therefore, the water table is usually higher during the dryer seasons or times of drought. Question: Could the height of the water table determine the amount of water usage we have.

AN ARTESIAN WELL Artesian water is a natural upward movement of water due to the fact that water is held under pressure between layers of impermeable rock.

Geysers Geysers are caused when underground chambers of water are heated to the boiling point by volcanic rock. When heat causes the water to boil, pressure forces a superheated column of steam and water to the surface. The initial amount of water released at the surface lessens the column’s weight, which also lowers its boiling point. When the boiling point drops, the entire column of water vaporizes at once, shooting out of the ground in a spectacular eruption. Fumaroles are similar to geysers, but release bursts of hot gases instead of water. Hot springs are supplied by the same sources as geysers, but these systems are under lower pressure, which causes water to bubble and pool at the surface instead of erupting. The water in these naturally heated springs often exceeds temperatures of 60° C (140° F).

Geysers Good “Old Faithful”

Geysers

STALACTITES AND STALAGMITES Ground water is composed of rainwater which is a weak acid because it contains carbon dioxide dissolved in water CO2 + H2O --> H2CO3 (carbon acid). If the rainwater flows over limestone, it may carry with it dissolved minerals. If ground water contains more than 8 grains of mineral per gallon it is referred to as "hard" water. "Soft" water contains very little dissolved minerals. Water is considered hard if it contains calcium sulfate, or calcium, magnesium and iron carbonates in solution. Calcium Carbonate (CaCO3) is the most common mineral in hard water. Hard water does not lather well when soap is added and it sometimes leaves a ring of deposits on tubs and sinks. Question: Do you have hard or soft water at your home? How so you know? If you do not know try to find out. Ground water transports many deposits and may help to concentrate these deposits of valuable minerals such as gold, silver, lead, copper. Sometimes petrified wood results when the wood fibers are replaced by silica (SiO2). Complete petrifaction takes many years. Stalactites are deposits of CaCO3 suspended from the ceilings of caves. Stalagmites are deposits of CaCO3 built up from the floor of a cave. Sometimes the two will meet and a column forms. Question: Have you ever been to a cave and seen stalactites and stalagmites? Share your experience with the class.

STALACTITES AND STALAGMITES

Stalactites and Stalagmites THE HYDROSPERE As you can see, hydrosphere is all around you. You have just seen a number of results of the water cycle; can you explain the following words. Runoff Zone of Aeration The Water Table Artesian Wells Geysers Stalactites and Stalagmites