Waves, Tides, and Currents

Waves A Wave is a disturbance that carries energy through matter or space. In oceans, waves move through seawater. Waves are the movement of energy, not matter.

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 Crest Wave Height Still Water Trough Wave Parts

Wavelength Long waves are called swells Short waves are called chop

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

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

Waves Caused by Wind When wind blows across a body of water, friction causes the water to move along with the wind. Wave Height depends on – Wind speed Fetch: Distance over which the wind blows Duration: Length of time the wind blows

Waves Approaching Shore 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.

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

Tsunamis They are produced by earthquakes and other disturbances of ocean surface water. Can also be caused by icebergs falling from glaciers and volcanic eruptions. They’re also called seismic sea waves.

Tsunamis are very long, fast moving waves! They can have wavelengths of 150 miles. They can travel at over 450 miles per hour! A wave formed off of Alaska can reach Hawaii in only 5 hours.

The Danger of Tsunamis In the open ocean, a tsunami may only have a wave height of a few feet. As the wave approaches shallow water, it builds to heights that can reach greater than 100 feet.

Tsunami History The 2004 Indian Ocean Tsunami was caused by an earthquake off the coast of Indonesia. The earthquake was the 2nd largest EVER recorded at a magnitude of 9.3 It was one of the deadliest natural disasters in recorded history. Indonesia, Sri Lanka, India, and Thailand were hardest hit. 229,866 people were lost, including 186,983 dead and 42,883 missing

Tsunami History 2011 Japan Tsunami Caused by 9.0 magnitude earthquake Friday, 11 March 2011 waves that reached heights of up to 40.5 meters (133 ft) confirmed 15,854 deaths, 26,992 injured, and 3,155 people missing The tsunami caused a number of nuclear accidents Fukushima Daiichi Nuclear Power Plant Residents within a 20 km (12 mi) radius were evacuated estimated economic cost was US$235 billion, making it the most expensive natural disaster in world history. National Geographic: Asian Tsunami

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. Tidal range is the difference in ocean level between high-tide and low-tide

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.

Gravitational Effect of the Sun Spring Tides Earth, Moon, and Sun are lined up (full or new moon) High Tides are higher and Low Tides are lower than normal

Gravitational Effect of the Sun Neap Tides Earth, Moon, and Sun form right angles (half moon) High Tides are lower and Low Tides are higher than normal

Atmospheric Circulation Is powered by sunlight. Because the sun hits different parts of the Earth at different angles, the Earth heats unevenly. The poles receive less solar energy than the equator.

Uneven Solar Heating and the Seasons The Earth rotates on a 23.5o tilt. Causes N Hemisphere to receive more light in June than the S Hemisphere but less in December. This also causes days to become longer as summer approaches and shorter as winter approaches.

Uneven Solar Heating and Atmospheric Circulation Warm-air rises and cool air sinks. Warm-air near the equator cools and sinks as it approaches the poles. Cool air near the poles rises as it warms near the equator.

Atmospheric circulation is also influenced by The Coriolis effect - The rotation of the Earth on its axis deflects the atmosphere toward the right in the Northern Hemisphere and toward the left in the Southern Hemisphere.

Ocean Currents There are a number of ocean currents found around the Earth. A current is like a vast river within the ocean, flowing from one place to another. These currents are caused by differences in temperature, differences in salinity, and by wind. Currents are responsible for a vast amount of movement of the water found in the Earth’s oceans.

Surface Currents Involve 10% of the oceans water. This water occupies the uppermost 400 meters of water. Usually above the pynocline. The Trade Winds propel ocean water westward along the equator, and when it strikes a continent, it is diverted poleward. In mid-latitudes the currents are driven eastward by the Westerlies.

Thermohaline Circulation Circulation of the oceans as a function of temperature (thermo) and salinity (haline) When water is cooled at the poles, it sinks Water from the equator moves poleward to fill in the "gap" As water from poles moves down and toward the equator, it is heated and rises.

Upwelling and Downwelling Upward movement of water is called upwelling Brings cold, deep, nutrient rich water to the surface Happens most near equator and on coastlines Causes increased biological productivity Downward movement of water is called downwelling Supplies deep ocean with dissolved gases