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Waves and Tides. Anatomy of a wave. Wave - the transmission of energy through matter When energy moves through matter as a wave, the matter moves back and forth or rotates, but then returns to its original position It transmits the energy to adjacent matter, allowing the energy to continue
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Anatomy of a wave • Wave- the transmission of energy through matter • When energy moves through matter as a wave, the matter moves back and forth or rotates, but then returns to its original position • It transmits the energy to adjacent matter, allowing the energy to continue • Drop a rock in a pond and you can see the waves move away from the splash, these are called progressive waves.
Progressive Waves • There are three types of progressive waves • Longitudinal waves- the matter moves back and forth in the same direction that the energy travels. Like a spring. • Transverse wave-The motion of the matter is perpendicular to the direction in which the wave as a whole is moving. • EX: shake the end of a taut horizontal rope up and down, the rope moves vertically but the wave travels horizontally along the length of the rope. • Orbital waves-Only transmit through fluids. They occur when the energy moves the fluid in a circular motion as it passes.
Wave Terminology • Crest- the highest point above the average water level • Trough- the lowest point • Wavelength- the horizontal distance between the identical point on two waves • Period- the time it takes for the same spot on two waves to pass a single point • Frequency- the number of waves that pass a fixed point in one second
Wave Causes and Characteristics • Wave Causes and Characteristics • Disturbing forces cause waves and restoring forces resist waves. The intensity and duration of a disturbing force and the interaction of the restorative force give waves their characteristics. • Disturbing forces- Examples include wind changes in gravity, seismic activity. Wind is the most common through the friction of air passing over the water surface. • Restoring forces- Examples include gravity, the coriolis effect, and surface tension.
Wind Waves grow due to friction with the air transferring energy to the water • As these waves grow they present more surface area to the wind, allowing more energy to transfer • There are 3 factors that affect the growth of wind waves • Wind Speed-the wind must be blowing faster than the wave to give it energy • Wind duration-the length of time the wind blows in a single direction • Fetch- the surface area over which the wind blows Example: strong winds over a pond will never create a huge wave because there isn’t enough time to transfer enough energy
Disturbing forces and restoring forces counterbalance the forces that cause wind waves and when an area has reached the maximum size it is called a fully developed sea • Rogue Waves can form when two wave trains that are in phase, crests and troughs coincide, combine making waves larger than the maximum size should be. They can also form if the waves go against the direction of the current.
Surface and Breaking Waves • Surface and Breaking Waves • As a wave approaches the shore the bottom will begin to influence the movement of the wave. • The bottom energy of the wave begins to slow down but the energy at the top of the wave gains speed • This causes the top of the wave to move beyond the bottom of the wave and the wave breaks • “The wave trips”
There are three different types of wave break: • Plunging breakers- are characterized by a curl as the top of the wave pitches through the air before splashing. Usually found on steep beaches that decelerate the wave quickly. Example: Seaside beaches • Spilling breakers- occur on gently sloping beaches. The top of the wave tumbles and slides down the front of the wave as it slowly decelerates. Example: Wildwood beaches • Surging breakers: Occur on very steep beaches that are almost like walls rising out of the deep water. The waves don’t interact with the bottom and never slow down so they have a tremendous amount of energy and are very destructive. Example: Point Pleasant
Destructive Waves • There are three distinct types of destructive waves • Storm surges- forms when high winds push water against the shore. The shallower the water offshore, and the further it extends offshore, the greater the surge. • When the storm moves ashore the storm surge builds on top of the tide • It becomes very destructive when the tide is extremely high
Seiches- is a standing wave that rocks back and forth in large bays and lakes • Can form when a strong wind pushes the water level up on one side of the lake or bay • When the wind subsides the water rocks back and forth and can cause coastal damage
Tsunami- results from sudden water displacement caused by a landslide, an iceberg falling into the sea from a glacier, a volcanic eruption, or an earthquake • Tsunami is Japanese for harbor wave • They are fast moving and can travel thousands of kilometers • The energy travels underwater and if not monitored by electronic devices can go undetected until it is too late. • Often the beach will recede drastically as if there were an extremely low tide, them minutes later the water comes rushing back with a tremendous amount of energy • Records have shown a tsunami surge to be as high as 1,740 in Alaska in 1958.
Tides • Tides- are daily variations in the ocean’s level. They are the result from the gravitational pull of the moon and to a lesser degree the sun. • The sun and moon create two bulges on the opposite sides of the Earth. • The relative positions of the sun and the moon change slowly, so the bulge rotates around the Earth. • As a coastline rotates into the bulge, the tide rises. As it rotates out, the tide falls
Tidal Patterns and Currents • Diurnal Tides-having a single high and low tide daily. Example: The Gulf of Mexico • Semidiurnal Tides- having two roughly equal high and low tides daily. Example: the east coast of the United States • Mixed Tides- having two unequal high and low tides daily. Example: the Pacific coast of the United States
Daily tides create a current that flows into and out of bays, rivers, harbors, and other areas. • Flood current- the inflow of water caused by a high tide • Slack current- the out flow of water caused by the low tide • Slack tide- occurs when there is little water moving between high and low tide
The sun has much more gravity than the moon but affects the tides less because it is so far away. • When there is a new moon (the moon is not visible) both the sun and the moon are aligned on the same side of the Earth • During a full moon, the sun and the moon are aligned on opposite sides of the Earth. • Both positions create the highest and lowest tides called spring tides • When the moon is in its quarter phase, the sun and the moon are at right angles to the earth and create lower high tides and higher low tides called neap tides
The Proxigean Spring Tide is a rare, unusually high tide. This very high tide occurs when the moon is both unusually close to the Earth (at its closest perigee, called the proxigee) and in the New Moon phase (when the Moon is between the Sun and the Earth). The proxigean spring tide occurs at most once every 1.5 years.
