waves, tides, and currents. waves a wave is a disturbance that carries energy through matter or...
TRANSCRIPT
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
Wave Height
Crest
Trough
Still Water
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
• 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.
Tsunami 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 sinksWater 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