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
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