Waves, tides, and hurricanes
Name: ______________________________________________________ Period: _____ Date: _______
Essential Question: How are waves, tides, and hurricanes formed?
Oceans cover more than 70% of Earth’s surface. About 97% of Earth’s water is contained in oceans and
seas. The five oceans—the Pacific, Atlantic, Indian, Southern, and Arctic—are all connected and form an enormous
mass of water. Seas are smaller bodies of salty water within the oceans. The oceans are salty, which makes them
unsuitable for drinking. Most of the salt comes from minerals from rocks and soil that have been washed from the
land and carried into the oceans by rivers. The minerals are mostly chloride and sodium, which combine to make
salt. Most of our table salt comes from the oceans.
The salinity, the amount of salt, varies in the oceans. Oceans in warm climates are saltier than the oceans
in cold climates. That’s because ocean water in warmer areas, near evaporates quicker, leaving more salt behind.
The saltiest water in the world is in the Red Sea, which is almost entirely surrounded by deserts. Why are oceans
near the equator saltier than the oceans near the poles?
Tides and waves, cause the oceans to move constantly. A tide is the regular rise and fall of the sea level in
oceans and other bodies of water. It is caused mainly the effect of the Moon’s gravity on Earth. Water on the side
of Earth that is closest to the Moon is pulled in the direction of the Moon, creating a bulge in the ocean. On the
other side of Earth, the Moon’s gravity pulls Earth away from the water, producing a matching bulge. These bulges
form high tides. Because the Earth rotates on its axis, every point on Earth (except the poles) travels through the
two high tide zones and the two low tides zones each day. This is why there are two high tides and two low tides
each day. Spring tides or higher high tides, which are especially strong, occur during new and full moons—every
two weeks—when Earth, the Moon, and the Sun are in alignment. Neap tides or high tides, which are weaker,
occur during first and last quarter moons, when the Sun, the Earth, and the Moon form a right angle.
Waves: Waves are caused by winds. As the wind blows over the surface of the ocean, it pushes on the water and
transfers some of its energy to the water. The water gets energy from the wind because of the friction between air
molecules and water molecules. It may seem that waves move forward or horizontally, but they do not. They move
up and down. You can see this by watching a buoy in the water. It bobs up and down with waves rather than
moving from side to side.
Hurricanes: Hurricanes are severe tropical storms that form in the southern Atlantic Ocean, Caribbean Sea, Gulf
of Mexico, and in the eastern Pacific Ocean. Hurricanes gather heat and energy through contact with warm ocean
waters near the equator. Evaporation from the seawater increases the power of hurricanes. In the northern
hemisphere, hurricanes rotate in a counter-clockwise direction around an “eye.” Hurricanes have winds at least 74
miles per hour. When they come onto land, the heavy rain, strong winds, and heavy waves can damage buildings,
trees and cars. The heavy waves formed by hurricanes are called storm surges. Storm surges are very dangerous
and a major reason why people MUST stay away from the ocean during a hurricane warning or hurricane.
Hurricane Classification:
Hurricanes are classified into five categories, based on their wind speeds and potential to cause damage.
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Category One—Winds 74-95 miles per hour
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Category Two—Winds 96-110 miles per hour
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Category Three—Winds 111-130 miles per hour
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Category Four—Winds 131-155 miles per hour
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Category Five—Winds greater than 155 miles per hour
In the U.S., the official hurricane season is from June 1 to November 30, but hurricanes can happen any time of the
year. Hurricanes are named by the National Weather Service. Some recent hurricanes have been named Opal,
Andrew, Marilyn, Hugo and Fran. Terms to Know: Hurricane Watch A hurricane is possible within 36 hours. Stay
tuned to the radio and television for more information. The Hurricane Center is tracking the storm and trying to
predict where it may come ashore. Hurricane Warning A hurricane is expected within 24 hours. You may be told to
evacuate. You and your family should begin making preparations to evacuate.
Clarifying Questions:
1. What are the five oceans of the world?
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2. Why is the ocean water unsuitable for drinking?
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3. Why are some oceans saltier than others? Think!
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4. What causes the ocean water to move constantly? Think!
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5. What mainly causes the tides?
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6. Explain why there are always two high tides and two low tides each day?
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Spring tide ( higher high tide)
Neap Tide ( high tide)
7. Describe the positions of the earth, moon and Sun during spring tide.
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8. Describe the positions of the earth, moon and Sun during neap tide.
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9. How do waves form?
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10. Where do hurricanes form?
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11. How do hurricanes increase their strengths? Think!
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12. In what direction do hurricanes rotate in the northern hemisphere?
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13. What is a storm surge?
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14. What is the difference between hurricane watch and hurricane warning?
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Matching type:
Hurricanes are classified into five categories, based on their wind speeds and potential to cause damage.
___15. Category One
___16. Category Two
___17. Category Three
___18. Category Four
___19. Category Five
A. Winds greater than 155 miles per hour
B. Winds 111-130 miles per hour
C. Winds 96-110 miles per hour
D. Winds 131-155 miles per hour
E. Winds 74-95 miles per hour