Tides Tides The rise and fall in sea

Tides

Tides • The rise and fall in sea level is called a tide. • Caused by a giant wave. • One low-tide/high-tide cycle takes about 12 hrs and 25 min.

Tides • Tides are caused mainly by the gravitational pull of the moon.

Other Things That Influence Tides • The gravitational pull of the sun. • The distance of the sun and the moon from earth. • Winds and other factors.

Tides (cont’d. ) • Tides tend to be high where the gravitational force between the earth and the moon are the strongest, along with the opposite side of the earth where the centrifugal force is strongest.

Tidal Range The difference in ocean level between high tide and low tide is called the tidal range

What is the Tidal Range? • HT = 30 ft LT = 20 ft • HT = 20 ft LT = 12 ft • HT = 50 ft LT = 20 ft

Spring Tides • Spring Tides have the greatest range –High Tides are higher and Low Tides are lower than normal • Occurs during the new and full moons. • Earth, Moon, and Sun are lined up

Neap Tides • Neap Tides have the least amount of range. • High Tides are lower and Low Tides are higher than normal • Occurs during the first and third quarters. • Earth, Moon, and Sun form right angles

Gravitational Effect of the Moon • Two big bulges of water form on the Earth: –one directly under the moon –another on the exact opposite side • As the Earth spins, the bulges follow the moon.

Waves

Waves • A Wave is a rhythmic movement that carries energy through matter or space. • In oceans, waves move through seawater

Waves Caused by: • Wind • Earthquakes • Gravitational force of the Moon and Sun.

Waves On The Beach • Most of the waves we see are at the beach.

Waves On The Beach • As the wave travels in shallower water it slows and eventually falls forward as a breaker.

Wind or Storm Waves • The most familiar waves are wind generated.

Wind or Storm Waves • Three things determine how large these waves can become.

1. Wind Speed • This is the speed that the wind is blowing. • This is usually measured in knots or nautical miles per hour.

2. Duration • Duration refers to the time over which the wind blows. • Winds in some areas may blow strong for long periods of time which can produce large waves.

3. Fetch • Fetch refers to the distance over which the wind blows. • If a wind blows over thousands of miles the waves can get much larger than blowing across a small pond.

Parts of a Wave • Crest – highest point of a wave • Trough – lowest point of a wave • Wave Height – vertical distance between the crest and the trough • Wavelength – horizontal distance between two crests or two troughs

Wavelength Wave Height Crest Still Water Trough Wave Parts

Wave Movement • When a wave passes through the ocean, individual water molecules move up and down but they do not move forward or backward.

Wave Movement • When a wave breaks against the shore, the crest outruns the trough and the crest collapses. • Called a breaker. • In this case, water does move forward and backward.

Waves Caused by Wind • When wind blows across a body of water, friction causes the water to move along with the wind.

Waves Caused by Wind • Wave Height depends on – –Wind speed –Distance over which the wind blows –Length of time the wind blows

Tsunamis • Tsunamis were once called Tidal waves, but they have nothing to do with the tides.

Tsunamis • They are produced by earthquakes and other seismic disturbances. That’s why they’re also called seismic sea waves.

Tsunamis • They are very long, fast moving waves. • They can have wavelengths of 150 miles. • They can travel at over 450 miles per hour! As fast as a jet!

The Danger of Tsunamis • In the open ocean, a tsunami may only have a wave height of a few feet.

The Danger of Tsunamis • As the wave approaches shallow water, it builds to heights that can reach greater than 100 feet.