Tsunami Oceans

Tsunami A tsunami (pronounced sue-nahm-ee) is a series of huge waves that can cause great devastation and loss of life when they strike a coast. Tsunamis are caused by an underwater earthquake, a volcanic eruption, an sub-marine rockslide, or, more rarely, by an asteroid or meteoroid crashing into in the water from space. Most tsunamis are caused by underwater earthquakes, but not all underwater earthquakes cause tsunamis - an earthquake has to be over about magnitude 6.75 on the Richter scale for it to cause a tsunami. About 90 percent of all tsunamis occur in the Pacific Ocean. Many tsunamis could be detected before they hit land, and the loss of life could be minimized, with the use of modern technology, including seismographs (which detect earthquakes), computerized offshore buoys that can measure changes in wave height, and a system of sirens on the beach to alert people of potential tsunami danger. NOTE: If you see the water recede quickly and unexpectedly from a beach (this is called drawback), run toward higher ground or inland -- there may be a tsunami coming. Also, if you are on the coast and there is an earthquake, it may have caused a tsunami, so run toward higher ground or inland. Some beaches have tsunami warning sirens -- do not ignore them. The first wave in a tsunami is often not the largest; if you experience one abnormally-huge wave, go inland quickly -- even bigger waves could be coming soon.

waves are caused by the wind.

The Word Tsunami: The word tsunami comes from the Japanese word meaning "harbor wave." Tsunamis are sometimes incorrectly called "tidal waves" -- tsunamis are not caused by the tides (tides are caused by the gravitational force of the moon on the sea). Regular

The Development of a Tsunami: A tsunami starts when a huge volume of water is quickly shifted. This rapid movement can happen as the result of an underwater earthquake (when the sea floor quickly moves up or down), a rock slide, a volcanic eruption, or another high-energy event.

After the huge volume of water has moved, the resulting wave is very long (the distance from crest to crest can be hundred of miles long) but not very tall (roughly 3 feet tall). The wave propagates (spreads) across the sea in all directions; it can travel great distances from the source at tremendous speeds. The Size of a Tsunami: Tsunamis have an extremely long wavelength (wavelength is the distance between the crest (top) of one wave and the crest of the next wave) -- up to several hundred miles long. The period (the time between two successive waves) is also very long -- about an hour in deep water. In the deep sea, a tsunami's height can be only about 1 m (3 feet) tall. Tsunamis are often barely visible when they are in the deep sea. This makes tsunami detection in the deep sea very difficult. The Speed of a Tsunami: A tsunami can travel at well over 970 kph (600 mph) in the open ocean - as fast as a jet flies. It can take only a few hours for a tsunami to travel across an entire ocean. A regular wave (generated by the wind) travels at up to about 90 km/hr. A Tsunami Hits the Coast:

As a tsunami wave approaches the coast (where the sea becomes shallow), the trough (bottom) of a wave hits the beach floor, causing the wave to slow down, to increase in height (the amplitude is magnified many times) and to decrease in wavelength (the distance from crest to crest). At landfall, a tsunami wave can be hundreds of meters tall. Steeper shorelines produce higher tsunami waves. In addition to large tsunami waves that crash onto shore, the waves push a large amount of water onto the shore above the regular sea level (this is called runup). The runup can cause tremendous damage inland and is much more common than huge, thundering tsunami waves. Tsunami Warning Systems: Tsunami warning systems exist in many places around the world. As scientists continuously monitor seismic activity (earthquakes), a series of buoys float off the coast and monitor changes in sea level. Unfortunately, since tsunamis are not very tall in height when they are out at sea, detection is not easy and there are many false alarms. Sirens at affected beaches may be activated -- do not ignore them! Wind-Generated Waves vs. Tsunami Waves:

Regular waves (caused by the wind) are very different from tsunami waves. Tsunami waves are much faster than wind-generated waves and they have a much longer wavelength (the distance from crest to crest). In the deep sea, tsunami waves are very small, but by the coast, they dwarf regular waves. How Often do Tsunamis Occur? Tsunamis are very rare. There are roughly six major tsunamis each century. Tiny Model of a Tsunami: You can make a tiny model of a tsunami by dropping a rock into a bowl of water, causing ripples to propagate (travel) outwards from the site of impact. Another way is to slightly jolt the bowl of water and watch it slosh over the rim on one side.

Why are the Oceans Salty? As water flows in rivers, it picks up small amounts of mineral salts from the rocks and soil of the river beds. This very-slightly salty water flows into the oceans and seas. The water in the oceans only leaves by evaporating (and the freezing of polar ice), but the salt remains dissolved in the ocean - it does not evaporate. So the remaining water gets saltier and saltier as time passes.

SALINITY Parts per Thousand chloride 19.3 o/oo sodium 10.7 o/oo sulfate 2.7 o/oo magnesium 1.3 o/oo calcium 0.4 o/oo potassium 0.4 o/oo bicarbonate 0.15 o/oo bromide 0.07 o/oo other 0.06 o/oo Total 35.08 o/oo Salinity Sea salts

The salinity (salt content) of ocean water varies. The oceans and seas contain roughly 5 x 10 16 tons of salts. One cubic foot of average sea water contains 2.2 pounds of salt. The oceans are about 3.5% salt (by weight). Salinity is generally reported in terms of parts per thousand (abbreviated o/oo), the number of pounds of salt per 1,000 pounds of water; the average ocean salinity is 35 o/oo.

The saltiest water is in the Red Sea and in the Persian Gulf, which have a salinity of about 40 o/oo (due to very high evaporation rates and low fresh water influx). The least salty seas are in the polar regions, where both melting polar ice and a lot of rain dilute the salinity.

WEB LINKS ABOUT SALT IN THE OCEANS Why is the Ocean Salty? By Herbert Swenson, a US Geological Survey Publication. Why is the Ocean Salty? from the Palo Alto Unified School District: Science On-Line Guide for Teachers. The Hydrologic Cycle from Agricultural and Biological Engineering at Purdue Univ.

WHY IS THE OCEAN BLUE? Sunlight is made up of all the colors of the rainbow: red, orange, yellow, green, blue, and violet. Some of the sunlight is reflected off the surface of the water, reflecting the color of the sky. Some of the sunlight penetrates the water and is scattered by ripples and particles in the water (this tinges the appearance of the ocean with the color of the particles). In deep water, much of the sunlight is scattered by the oxygen in the water, and this scatters more of the blue light. Water absorbs more of the red light in sunlight; the water also enhances the scattering of blue light. Sir Chandrasekhar Venkata Raman (an Indian physicist) won the Nobel prize in 1930 for his work on light. Some Oddly-Colored Seas: The Red Sea often looks red because of red algae that live in this sea. The Black Sea looks almost black because it has a high concentration of hydrogen sulfide (which appears black). Links: A page on the ocean's color from Charles L. Braun and Sergei N. Smirnov, Dartmouth College Ocean images from NASA

What Causes Waves?

The winds cause waves on the surface of the ocean (and on lakes). The wind transfers some of its energy to the water, through friction between the air molecules and the water molecules. Stronger winds (like storm surges) cause larger waves. You can make your own miniature waves by blowing across the surface of a pan of water. Waves of water do not move horizontally, they only move up and down (a wave does not represent a flow of water). You can see a demonstration of this by watching a floating buoy bob up and down with a wave; it does not, however, move horizontally with the wave. Tsunamis (sometimes called tidal waves) are different from surface waves; they are usually caused by underwater earthquakes, volcanic eruptions, or landslides. Related Pages:

Tsunami

Read about tsunamis: how they form and propagate, what the name tsunami means, and the speed and sizes of tsunamis.

The Great Wave Off Kanagawa Color a page of the Great Wave Off Kanagawa by the Japanese painter and printmaker Katsushika Hokusai (from the 1700s).

TIDES WHAT CAUSES THE TIDES?

Tides are periodic rises and falls of large bodies of water. Tides are caused by the gravitational interaction between the Earth and the Moon. The gravitational attraction of the moon causes the oceans to bulge out in the direction of the moon. Another

bulge occurs on the opposite side, since the Earth is also being pulled toward the moon (and away from the water on the far side). Since the earth is rotating while this is happening, two tides occur each day. Isaac Newton was the first person to explain tides scientifically. For information on the moon, click here.

The Sun's Interaction with the Tides Spring Tides

Spring tides are especially strong tides (they do not have anything to do with the season Spring). They occur when the Earth, the Sun, and the Moon are in a line. The gravitational forces of the Moon and the Sun both contribute to the tides. Spring tides occur during the full moon and the new moon.

The eccentricity of the orbit of the moon in this illustration is greatly exaggerated.

The Proxigean Spring Tide is a rare, unusually high tide. This very high tide occurs when the moon is both unusually close to the Earth (at its closest perigee, called the proxigee) and in the New Moon phase (when the Moon is between the Sun and the Earth). The proxigean spring tide occurs at most once every 1.5 years. Neap Tides

Neap tides are especially weak tides. They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another (with respect to the Earth). Neap tides occur during quarter moons.

WEB LINKS ON TIDES NOAA on tides Tides from the Department of Geography, Okanagan University College

Hurricanes

Hurricanes rotate in a counterclockwise direction.

A hurricane is a powerful, rotating storm that forms over warm oceans near the Equator. Another name for a hurricane is a tropical cyclone. Hurricanes have strong, rotating winds (at least 74 miles per hour or 119 kilometers per hour), a huge amount of rain, low air pressure, thunder and lightning. The cyclonic winds of a hurricane rotate in a counterclockwise direction around a central, calm eye. If this type of storm forms in the western Pacific Ocean, it is called a typhoon. Hurricanes often travel from the ocean to the coast and on to land, where the wind, rain, and huge waves can cause extensive destruction. Generally, when a hurricane moves over land (or over cold ocean waters) the storm begins to weaken and quickly dies down because the storm is fueled by warm water. On average, there are about 100 tropical cyclones worldwide each year; 12 of these form in the Atlantic Ocean, 15 form in the eastern Pacfic Ocean and the rest are in other areas. Hurricane season is the time when most Atlantic Ocean hurricanes occur; it is from June 1 until November 30. In the eastern Pacific Ocean, hurricane season is from May 15 until November 30.

The weather symbol for a hurricane is: . The marine flags that alert boaters to a hurricane are two square red banners, each

with a black square in the middle:

.

Hurricanes Introducti Hurrica Preparin Landfa Hurrica Hurrica How Naming Hurricane Tracking on to ne g for a ll, ne ne Hurrican Hurrican Classificati Hurrican Hurricane Structur Hurrica Storm Activiti Glossar es Form es on es s e ne Surges es y

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The Watercycle

The Water Cycle (also known as the hydrologic cycle) is the journey water takes as it circulates from the land to the sky and back again. The Sun's heat provides energy to evaporate water from the Earth's surface (oceans, lakes, etc.). Plants also lose water to the air (this is called transpiration). The water vapor eventually condenses, forming tiny droplets in clouds. When the clouds meet cool air over land, precipitation (rain, sleet, or snow) is triggered, and water returns to the land (or sea). Some of the precipitation soaks into the ground. Some of the underground water is trapped between rock or clay layers; this is called groundwater. But most of the water flows downhill as runoff (above ground or underground), eventually returning to the seas as slightly salty water.

WHY ARE THE OCEANS SALTY?

Oceans cover about 70% of the Earth's surface. The oceans contain roughly 97% of the Earth's water

supply.

As water flows through rivers, it picks up small amounts of mineral salts from the rocks and soil of the river beds. This very-slightly salty water flows into the oceans and seas. The water in the oceans only leaves by evaporating (and the freezing of polar ice), but the salt remains dissolved in the ocean - it does not evaporate. So the remaining water gets saltier and saltier as time passes.

Web Links On the Water Cycle and the Oceans

Water Cycle Diagram: Label Me! Printout Water Cycle Find It! Quiz Label the diagram of

Readers Theater Script: Water Cycle Adventure

A short play for students to read while learning about the hydrologic cycle - A quiz on the Earth's water the water cycle.

how water circulates on earth. Answers

cycle to solve using the Little Explorers picture dictionary.

The Earth's Oceans Learn all about the Earth's oceans.

The Water Cycle from the Univ. of Michigan The Hydrologic Cycle from Agricultural and Biological Engineering at Purdue Univ.

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ALL ABOUT OCEANS AND SEAS Undersea Explorers BALLARD, ROBERT

Robert Duane Ballard (June 30, 1942 - ) is an American undersea explorer, marine scientist, and US Naval officer who has been on over 65 underwater expeditions in submarines and deep diving submersibles. He found the Titanic and many other wrecks. Ballard has revolutionized undersea exploring by using remotely controlled submersible robotic devices (including Argo-

Jason; Argo is a remotely controlled submersible vehicle with cameras, and Jason is carried in Argo and sent from it to collect samples and perform other functions). Ballard founded the JASON project and continues to explore the sea. For more information on Ballard, click here.

BEEBE, WILLIAM

William Beebe (1877 - 1962) was an American naturalist and undersea explorer. In 1932, Beebe and Otis Barton descended 3,000 ft (914 m) in a bathysphere (a pressurized steel sphere invented by Beebe and Barton). They descended off the coast of Nonsuch Island, Bermuda, in the Atlantic Ocean. During the dive, they communicated with the surface via telephone. Beebe wrote many books detailing this and his other adventures around the world.

COUSTEAU, JACQUES

Jacques-Yves Cousteau (1910-1997) was a French undersea explorer, environmentalist, and innovator. In 1943, Cousteau and the French engineer Emile Gagnan invented the aqualung, a breathing apparatus that supplied oxygen to divers and allowed them to stay underwater for several hours. Cousteau traveled the world's oceans in his research vessel "Calypso," beginning in 1948. (Calypso was a converted 400-ton World War 2 minesweeper; it sank in 1996, after being hit by a barge in Singapore harbor). Cousteau's popular TV series, films and many books [including "The Living Sea" (1963), and "World Without Sun" (1965)] exposed the public to the wonders of the sea.

EARLE, SYLVIA

Sylvia Alice Earle (August 30, 1935- ) is an undersea explorer, marine biologist (specializing in botany), and author. Earle has done pioneering work in studying ocean life, and she has helped develop the equipment necessary for underwater exploration. During 50 underwater expeditions and over 6,000 hours underwater, Earle has discovered many new marine species and set many diving records. In 1970, Earle led a team of five aquanauts (underwater explorers) who lived for 2 weeks (during which they experienced an underwater earthquake) in an underwater laboratory in a U.S. government project named "Tektite II." She has discovered many underwater phemonena, including undersea dunes in the Atlantic Ocean off the Bahama Islands. For more information on Earle, click here.

PICCARD, JACQUES

Jacques Ernest-Jean Piccard (1922- ) is a Swiss ocean explorer and scientist who was the first person to go to the deepest parts of the Pacific Ocean. On January 23, 1960, he and U.S. Navy Lt. Don Walsh descended over 35,802 feet or 7 miles (10,912 m) in a pressured bathyscape, called Trieste. They went to the bottom of the Challenger Deep of the Marianas Trench (200 miles southwest of Guam), the deepest place on Earth. The trip took five hours. The bathyscape was built by Piccard and his father, Auguste Piccard (1884-1962), a notable Belgian physicist and inventor. Search EnchantedLearning.com for your explorer: Enchanted Learning® Web Page

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