Waterfall

   Waterfall, or Cataract, is the fall or per-pendicular descent of water from a stream or river, found mostly in mountainous regions. It is usually the result of a geológi¬ca! upheaval in which ¡mínense masses of rock were shifted hundreds of feet from their former position. In geologic time whole areas were thus elevated and others depressed, and in favorable locations where the fault was abrupt, waterfalls were formed. Subsequent changes resulted from erosion of rocks of different hardness. A remarkable series of waterfalls exists along the inward edge of the Atlantic coastal plain, in the neighborhood of the cities that lie between Trenton, N. J., and Augusta, Ga. Mountain cataracts or cascades make the highest waterfalls. Some of the most important waterfalls and cataracts are: The Falls of Yosemite in California, over 2,500 feet, the highest in the world; the Oroco Falls at Monte Rosa, Switzerland. over 2,000 feet; Victoria Falls in Africa, over 420 feet; Niagara Falls, 165 feet, and Iguassu Falls on the Iguassu River, which separates Argentina and Brazil. In high water the Iguassu Falls are greater in volume than Niagara Falls and are much greater both in height and width; the Gavarnie Falls in the Pyrenees are 1,385 feet; and the Staubbach Falls, Switzerland, 908 feet. Other celebrated waterfalls of the world are: Bridal Veil, Yosemite Park, 620 feet; Chamberlain, British Guiana, 300 feet; Fairy, Rainier Park, 700 feet; Gersoppa, India, 830 feet; Granite, Rainier Park, 350 feet; Illilouette, Yosemite Park, 370 feet; Kalambo, South Africa, 1,400 feet; Multnomah, Oregon, 850 feet; Nevada, Yosemite Park, 594 feet; Ribbon, Yosemite Park, 1,612 feet; Rjukan, Norway, 780 feet; Roraima, British Guiana, 1,500 feet; Skjaeggedalsfos, Norway, 530 feet; Sluiskin, Rainier Park, 1,300 feet; Sutherland, New Zealand 1,904 feet; Takkakaw, British Columbia, 1,200 feet; Vettis, Norway, 950 feet; Voringfos, Norway, 600 feet; Wid-dows' Tears, Yosemite Park, 1,170 feet.

What makes geysers?

A geyser is a special kind of spring. Water squirts out of it in jerks, instead of coming in a steady flow, and geyser water is boiling hot.
Hot springs can exist where hot liquid rock is trapped inside solid rock, deep underground. But two special things are needed before a hot spring can become a geyser: (1) underground cavities in which water can collect; and (2) a narrow tube leading from the cavities up to the surface.
Here is how a geyser works. Water collects in the cavities. Heat from the liquid rock far below reaches this water and makes it boiling hot. But it can't behave the way ordinary boiling water behaves in a pan on the stove. In the pan, boiling hot water turns to steam; the steam rises from the bottom, and flies off into the air. But the hot water in the geyser cavity can't escape so easily. Remember, there is only a long narrow tube leading to the air outside. The cold water in it acts somewhat like a huge cork in a bottle. The steam can't escape because of the cork. The temperature of the water goes up and up. Still it can't let off steam. Gradually tremendous pressure builds up way down inside the cavity.
Read more »

What is frost?

Frost may be like a fairy forest on a windowpane in the winter. Frost is ice. It is formed when moist air comes against something very cold. The water vapor in the air freezes.
Frost on Windows is on the inside of the Windows. The moisture comes from the warm air inside the building. The Win¬dows are cooled by the cold air outside. The frost on Windows is like the frost that forms on the coils of an electric refrigerator, but it is in much prettier patterns.
In the fall frost of ten forms on grass and roofs and bushes. Of course, it does not form unless the temperature goes below freezing. If the temperature is above freezing, dew forms instead.

What is Winter Sleep?

Hibernation, or Winter Sleep, is the torpid condition in which certain animals pass the winter in cold countries. The phenomenon is of commonest occurrence in cold-blooded species whose temperature rises and falls with that of the surroundings, but it is practiced by a considerable number of warm-blooded mammals which normally possess the capacity of keeping their temperature at approximately the same level, irrespective of the temperature of the air. It is in these that the physiological accompaniments of hibernation have been chiefly studied, and the principal changes are as follows: The temper¬ature falls to within a few degrees of that of the air, and the heart-beat becomes slow and feeble; respiration almost stops; the alimentary canal and excretory organs cease to operate, but life is maintained by the absorption of fat stored in the tissues during autumn.
Read more »

The sea as a sculptor

The power of the sea

The power contained in a breaking wave is immense. A wave may strike the shore with a force equal to the pressure of six thousand pounds per square foot. These waves can hollow out or pull down rock cliffs. In some parts of the British Isles they are eating away the coast at the rate of 15 feet a year.
  Storm waves tend to tear down the shores. Gentle waves are the builders, for they may leave numberless grains of sand against offshore bars to build up new beaches.
  Behind these new sheltering sand bars, tidal marshes grow up. They are built of sediment left by waves and washed down from the land by streams.
  Miles of new land like this are built along shorelines where the land has been lifted up so that a gentle slope of the continental shelf is now above water. There are many such beaches along the southeastern United States. For every cliff that crumbles under the hammering of the sea, somewhere a new beach is being built, a new coral reef is growing, or a new volcanic island being thrust up.
  The sea and its shores are ever changing. As glaciers grow or melt, they greatly change the amount of water in the seas. Earthquakes change the shapes of ocean basins. There was a time when much of North America was covered by sea. At other periods Alaska and Siberia were joined by a land bridge, and most of the East Indies were a part of Asia—so high did the land masses rise.
  There will be other changes in the future which we cannot foresee. We can only be sure that through the ages the sea will continue its miraculous labor.

Three types of waves

   Most people think of a "wave" as meaning any vertical rise or swelling of the sea. Actually there are three types of waves.

   When a wave first forms in wind-blown water, it is called a sea. When it has left the storm area and is traveling across calm water, it is a "swell." When it reaches land and breaks, it is "surf."

   The height of a storm wave, or sea, depends on violence of the wind, length of time the storm lasts, and extent of open water over which the storm rages. Most seas are only 5 to 12 feet high, but a two-day storm may produce 20-foot waves. Even 50-foot waves have been reported.

   Each drop of water in a wave moves in a cir¬cular pattern, as if on a wheel. For a drop near the surface this circle is the height of the wave; deeper down the circle is smaller. Any one drop of water moves ahead at only 1 to 2 percent of the speed of the wave. At about 600 feet or more below the surface, the sea is alwavs calm.

   Swells travel under their own momentum across wide areas of windless water. They are low, widely spaced, and fast-moving. They keep traveling in an orderly pattern to far-distant shores. As they travel, their height lessens, the spacing between waves lengthens, and their speed increases. Eventually a swell may travel faster than the wind that set it in motion.

   When it nears a shore, the wave "feels bottom." Slowed by friction against the sea bottom, it rises from a low swell to a narrow, steep crest. The crest hurries forward faster than the slowed-down wave. Breaking into foam, it tumbles forward in a burst of fury onto the sand.

Sea Waves

What is Fog?

   A fog is a cloud close to the ground. Clouds are made of tiny drops of water. So are fogs. There may be so many of these droplets that they shut off the view of everything round about. There are many accidents in fogs because people cannot see their way.
   Fogs occur most often near big bodies of water. The land often cools off much faster than the water. Warm, moist air moving in over the land is cooled quickly. Some of the water vapor in the air changes to drops of water and forms a fog. In cities fog may have so much smoke mixed with it that it is called "smog."
Some cities are famous for their fogs. London is one of them.
   Fogs disappear when the ground warms up or when a brisk wind blows them away. They can be driven away by fires. During World War II millions of dollars were spent to keep airfields free of fog.

What is sleet?

Sleet is a form of precipitation consisting of frozen or partly frozen rain, usually accompanied by snow or rain. Particles of sleet are formed in cold weather when raindrops enter an area of very cold air and become supercooled, i.e., cooled below their freezing point without freezing. The drops freeze suddenly when they come in contact with solid objects, such as particles of dust, and form a shower of small, round, white pellets of ice. When the drops fall on larger objects, such as telephone wires or tree branches, they form a coating of ice.

Sleet

When the Monsoon Comes

Moonson rain

  No single element plays a more decisive role in the life of the far-flung realm of tropical Asia than the rain. On the plains of India, in parts of Burma, Thailand and Indonesia, where it is dry and dusty for half the year, men, plants and animals build their lives around the expectation of the seasonal rains— and when they come, they come on walls of towering clouds and change the landscape from seared brown to verdant green, from parched river bed to raging torrent. In other parts of the region, from the Malay Península southward and southeastward through the great are of the islands, steady rain throughout most of the year has shaped flora and fauna up to the highest mountain ridges. The ultimate determinants of this type of climate which is so characteristic of the Oriental region are winds—the monsoon winds, whose name derives from the Arabic word mausim, or "season." There is a regularity to these winds which has long fascinated meteorologists, and even today the challenging question of just why they blow at the times and in the manner that they do has not been answered to the entire satisfaction of the scientific mind. Basically, they arise from low pressure areas created by the heat of the sun in tropical regions. Where pressures are low, air from surrounding areas moves in—and these movements are felt tangibly as winds. In the heated, low pressure areas, the air rises, flowing outward at the apex of its rise, north and south in the respective hemispheres, toward the poles.
In Southeast Asia, this "weather machine" is peculiarly affected by the differential heating between land mass and ocean. Asia is the largest of the world's land masses, and in summer the sun, blazing down on its arid interior, warms the earth to such torrid extremes that the equatorial low pressure system moves northward toward the Tropic of Cancer. This now becomes the dominant low for the season, drawing in increasing air masses from surrounding regions— and the air that pours in from the south is saturated with moisture drawn up from the southern seas. All along the island are and over the drought-parched Indian plains this moisture-laden air, moving toward the heart of Asia, raleases its burden as rain.

What are biomes?

Why do animals live where they do? Zoological realms provide only partial answers to this question; hence the concept of the biome, a smaller region. In the biome, now generally defined as an area controlled on land by climate, and distinguished on land or in the sea by the dominance of certain types of plants or ani¬mals, ecological relationships can be closely studied. Thus, for example, in colder regions a coniferous forest biome stands revealed: a forest dominated by cold-resisting evergreens whose superior adaptations and utilization of the available light, water and mineral nutrients limit the growth of other types of plants— and strongly influence the animal population.

BIOMES

Coniferous Forest
Young spruces and first begin to crowd out deciduous aspens in the coniferous forest bi¬ome. Evergreens domínate this broad belt, some 400 to 800 miles wide, which stretches across Canada, Alaska and Eurasia and, farther south, covers high mountains. Moose are found in the northern area, mule deer in the western mountains. One bird, the red crossbill, has a beak so specialized for picking seeds from cones that it can live only here.
Read more »

The saltiness of seawater

We have already know that cold water is heavier than warm and tends to sink. Salt, too, can make water heavy. On the whole, the proportion of salt in the open sea stays close to 3.5 percent. Near melting polar ice, however, the water tends to be less salty because the ice that is melting is nearly fresh. By contrast, the water near ice that is begin¬ning to form will have more than an average amount of salt since the ice that is in the process of freezing leaves extra salt behind in the water. Since this kind of water—both cold and salty—will sink the deepest, the heaviest water is found at the very bottom of the sea. Heavy water of this sort, loaded with salt from beneath the antarctic ice shelf, rides the ocean floor all the way to the equator and across it into the Northern Hemisphere. The ride takes a long time. Some scientists figure that 300 years pass before a bit of cold, salty, deep water goes from the Antarctic to the equator. Others say that it takes 1,500 years. By contrast, a bit of warm, relatively unsalty water may take only a year to make the surface circuit of the North Atlantic wheel.
Read more »

Why is water an important solvent?

  Of all the different substances that can be solvents, water is the most important. Water carries dissolved nutrients in the body fluids of living things. Many of the liquids you use every day are water solutions.
  Water can dissolve so many different substances that it is often called the universal solvent. What makes water so special? The oxygen atom of a water molecule holds electrons more strongly than the hydrogen atoms. The shared electrons in the two covalent bonds, therefore, are drawn closer to the oxygen. As a result, the oxygen takes on a slightly negative charge and the hydrogens a slightly positive charge. Because of the molecule's shape, one end is positive and the other end negative.
  Water molecules can act as little magnets. The positive ends of water mole¬cules are attracted to solute particles that have a nega¬tive charge. The negative ends of water molecules are attracted to positively-charged solute particles.
  Water dissolves most ionic solids because its molecules pull apart the ions that make up the solid. Water can also form a solution with molecules that have slightly negative and slightly positive parts. However, because molecules of fats and oils have their electrical charges evenly distributed, they repel water molecules instead of attracting them.

How earthquakes happen?

  Earthquakes occur at cracks in the Earth's crust called faults. Faults are created because rock is brittle and breaks when great stress (stretching, squeezing or twisting) is exerted upon it. Stress builds up in areas of the crust because of the gradual movement of the Earth's plates.
  Earthquakes happen when stress has built up in an area of rock to such an extent that sudden movement occurs. This movement can create a new fault as the rock breaks at the weakest point, or the movement causes the rock to slip along an existing fault. When this happens, an enormous amount of enorgy is given out as the stress is released. The released energy causes the surrounding rock to vibrate, which creates an earthquake
The actual point where the rock first slips or breaks, causing an earthquake, is called the focus. The place on the Earth's surface immediately above the focus is called the epicentre.


Shock waves
  The vibrations of an earthquake travel out through the Earth. Scientists call them shock waves or seismic waves (from the Greek word seismos which means "trembling Earth"). Different types of shock waves are sent out from the focus, and each type makes the rock it travels through víbrate in a different way.
  The main types of shock waves are called primary and secondary waves. Primary waves, or P-waves, squeeze and stretch the rock they travel through. Secondary waves, or S-waves, move the rock up and down, like a roller coaster, and also sideways at the same time. Other types of shock waves, called surface waves, have other shaking effects. These do not occur in all earthquakes, but when they do occur, they are capable of causing damage far away from the epicentre.

Mauna Loa, the largest active volcano

eruption at Mauna Loa

  Mauna Loa (Long Mountain) lies to the south of Mauna Kea and, like it, rises from a plain 18,000 feet below sea level. Mauna Loa is 13,675 feet high; it is the largest active volcano in the world. Its dimensions are quite staggering; it is about sixty miles across and two hundred miles in circumference at sea level. At the summit there is a huge crater, which is called Mokuaweoweo. This crater is five miles in circumference; the cliffs around its pit are from 500 to 600 feet high. There is considerable volcanic activity in Mokua¬weoweo, particularly before an eruption; white-hot fountains of lava rise to a height of several feet. However, there have been no flows of lava from this crater, at least in historie times. All the lava discharges from Mauna Loa come from the flanks of the mountain, at elevations of from 7,000 to 13,000 feet.

Some historic Mauna Loa lava flows
  There have been numerous eruptions in the past hundred years or so, at intervals of a few years. The eruption of 1873-74 lasted eighteen months; that of 1880-81, nine months. In 1926, a lava flow from a crevice in the southeastern side of the mountain destroyed the village of Hoopuloa, on the coast. This flow was thirty feet high, and advanced along a front of about a hundred feet at the rate of three feet a minute. Thomas A. Jaggar, director of the Hawaiian Volcano Observatory, compared the flow to the lumbering advance of a caterpillar tractor. Said he: "An upper layer of boulders and paste is rolled forward on a viscous red-hot paste inside, tumbles down at the front in a debris slope and this is eternally overridden by the advancing mass for which it lays the track."
  In 1935, the city of Hilo was threatened by a lava flow proceeding from the northwest flank of Mauna Loa. The United States Army Air Corps (it is now a sep¬arate military arm) came to the rescue. A fleet of bombers dropped 6,000 pounds of bombs from a height of about 5,000 feet above the lava. The bursting bombs opened up new channels for the lava flow, diverted its course, and saved the city.

What makes glaciers?

   Glaciers are rivers of ice. They actually flow, and they really are made of ice. Wherever glaciers are found, the average temperature for the whole year is below freezing. This means that ice can last, year after year, even if some of it melts in summer. But where does the ice come from in the first place?

   It comes from snow which can change into ice in two different ways. When the sun melts the surface of snow, water seeps down and melts more snowflakes underneath. But the temperature deep in the snow is still below freezing. When the seeping water reaches this super-cold snow, it changes to ice.

   But this is not the main way in which snow becomes glacial ice. Snow piles up so deep that the individual snowflakes are pressed close together. When this happens, the tiny snow crystals begin to act according to a special habit they have. The smaller snowflakes join larger ones. The result is new and larger snowflakes or crystals. These crystals then join still larger ones, and so on until solid crystals the size of marbles have been formed. Sometimes in very big glaciers the crystals grow to the size of baseballs.

   Glaciers would be mountains of ice getting higher every year if gravity didn't pull on them and make them move downward from the places where they form. Glaciers move slowly, compared to rivers of water, but they do move.

What makes lightning?

   Lightning is really electricity — lots of electricity that jumps through the air in huge sparks.
You can make little jumping sparks of electricity if you rub a cat's fur or comb your hair with a hard rubber comb. Probably the giant sparks of lightning are caused in somewhat the same way.
   Lightning sparks start in the clouds. Great winds blow through a rain cloud and whip the raindrops around and tear some of them apart. Tremendous action goes on, and this action electrifies the cloud. Weather-men don't know exactly how it happens, but great charges of electricity build up. Suddenly there comes a flash. The lightning jumps from one part of the cloud to another. Or it leaps between the cloud and the earth.
   Lightning usually seems like one enormous quivering spark, but it is really several sparks. It travels in a zigzag path, and that is what gives it a jagged look.
   If you could stretch electric cords from the ground to the clouds, there wouldn't be any lightning. The electricity would run through the cords into the earth. Of course, we can't plug cords into the clouds. But people often do have metal lightning rods that stick up above houses and barns. The electricity jumps from the cloud to the rod. Instead of hitting the building, it runs into the earth.