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Waves Edited learning goals.docx

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Department
Earth and Ocean Sciences
Course
EOSC 114
Professor
All Professors
Semester
Winter

Description
Waves learning goals Waves : 1. Identify key properties of waves 1. Crest - the highest point of a wave 2. Trough - the lowest point of a wave 3. Wavelength (L) - distance for one cycle - unit: meters 4. Wave height (H) - distance from crest to trough 5. Amplitude (A) - Distance from crest or trough to ocean surface a. A = wave height/ 2 - Units: meters 6. Steepness - ratio of wave height to length a. Steepness = wave height/wave length - no units 7. Period (P or T) - time for one wavelength to pass a point - unit: seconds 8. Frequency - number of waves in a certain period of time - units: hertz, 1/seconds 9. Celerity - wave speed a. C= wavelength/period - units: meters per second 2. Use these properties to determine wave speed and behavior in either shallow or deep water In deep water, the movement of the water is negligible, in more shallow water, the speed decreases, height increases, steepness increases, period remains the same, orbitals become elliptical, and waves break. Deep water wave depth is greater than or equal to wavelength over 2, and shallow water, depth is less than or equal to wavelength over twenty. Deep water speed c = L/t – depends on wavelength, shallow water c = 3.1 root of d – depends on depth.  1. Deep water waves (when water depth > wave base) - water does not touch the bottom, so wave speed is dependent on wavelength 2. Intermediate waves (when water depth < wave base) - water feels the bottom, so it moves in flattened orbitals. So the speed is slower 3. Shallower-water waves (when water depth << wave base) - water feels the bottom, and moves horizontally back and forth. So wave speed is dependent on water depth 3. Explain how waves move matter and energy Water moves back & up, then and down & forward CIRCULAR motion (orbits) ENERGY passes through the water, but there is only NEGLIGIBLE NET MOVEMENT of the water i.e. Water moves in a circular motion, energy passes through the water, but there is only negligible movement of the water. Wave orbitals are largest at the surface, and decrease as they go downwards.  At depth > l/2, there is no movement.  Waves transport energy through a medium (Energy + medium = wave) Requires an energy source, aka a generating force, and a medium to travel through, ex. Ocean. 4. Describe the forces that generate waves, eliminate waves, and return the ocean to a flat, undisturbed surface (pics taken from the slides) 1. Generating forces - add energy in to the system. They cause the disturbance to create waves. Ex. Gravity, impacts, wind 2. Restoring forces - a generating force that disturbs the surface and distributes energy. Rebound a surface, and allow waves to spread. Ex. Gravity and surface tension enable waves by rebounding a surface disrupted by a wave to bring it back to neutral level. 3. Eliminating forces - take energy out of the system, destroying waves, by transferring energy to heat and particle motion. Ex. Turbulence, friction along the sea floor, heat or kinetic energy lost through spray 5. Explain the factors that determine the roughness of the sea 1. Wind speed 2. Wind duration 3. Fetch - uninterrupted distance over which wind blows Fully developed sea happens when: Energy IN is from the wind = Energy out from breaking  Beaufort scale based on wind speeds and damage. 6. Describe how waves interact; explain constructive and destructive interference  waves are reflected by hitting anything solid  Wave interactions occur when: 1. They are traveling in different directions 2. They are traveling at different speeds  Wave interference can be: a. Constructive Interference is when the troughs and crests of waves line up and this results in bigger waves and higher energy packets b. Destructive interference is the opposite it is when the troughs lines up with the crests and this results in smaller waves and smaller energy packets 7. Describe wave refraction, seiche (standing waves in enclosed or semi- enclosed bodies), and resonance; how do these affect the coast and people?  Refraction occurs when: 1. Waves approach the shore at an angle 2. Waves in shallow water slow and bunch up, while offshore waves in deep water simultaneously continue and spread 3. Causing waves bends toward the shore  The affect of resonance in a water body: 1. When waves are in a semi-enclosed space and wave frequency matches natural frequency, 2. energy is maximized leading to waves reflecting perfectly, 3. leading to constructive interference, which enhances wave height and creates standing waves and exacerbating wave damage 4. Note: Size determines natural frequency à meaning that larger bodies have longer period  Characteristics of a Seiche: 1. Period depends on geography - Fixed 2. Height depends on generating energy - Variable a. Wind - blows water to one end b. Earthquake - vibrates water c. Impact - displaces water d. Tsunami - water enters bay from ocean 8. Relate wave interference and resonance to marine hazards Merging storm waves: 1. Storm waves can combine to make larger waves 2. Waves and winds heading straight into powerful ocean currents may cause a sure of water to rise out of the deep (aka Rogue waves) Rogue Waves are: 1. Huge waves resulting from constructive interference 2. Unpredictable 3. Appear and disappear quickly 4. 3-4 times taller that surrounding waves 5. Extremely steep and dangerous 6. Most common near Agulhas current, near South Africa  Resonance waves can cause seiches when the two periods sync up 9. Describe how tsunami form and how they are detected  What causes a tsunami: 1. Meteorite impact 2. Earthquake vertically moving ocean floor: the vertical fault motion transmits energy to the water column, ie. Large subduction- related earthquakes cause this motion. 3.Volcanic eruption 4. Landslide into water, or a submarine landslide 5. Iceberg calving from a glacier into ocean  nothing happen when two plates slide beside each other, there must be vertical motion for a tsunami to happen.  Most tsunamis are generated in the ring of fire due to subduction earthquakes and related submarine landslides  How are tsunamis detected: D
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