Wave Properties and Ocean Wave Formation

• Waves propagate and transport energy
• The medium matter can be water, rock, ground, or air
• As waves pass, matter moves, but the net motion is zero
• Body waves are entirely within the same medium
• Surface waves move between two media
• Waves have varying speeds

Ocean Wave Formation

• Ocean waves form from disturbance forces like wind, earthquakes, and gravity
• Energy is propagated through water, acting as the medium
• Surface waves travel between air and water
• Water moves as waves pass, with no net motion
• Waves are generated by wind and geological activity

Essential Wave Properties

• Crest: highest point of a wave
• Trough: lowest point of a wave
• Wavelength (L or λ): distance between crest-to-crest or trough-to-trough
• Height: vertical distance from crest to trough
• Amplitude: height/2
• Steepness: height/wavelength
• Period (T): time for a wavelength to pass a point or the time for two crests to pass
• Frequency (F): number of waves per time period, measured in Hertz (Hz)
• Celerity (C): distance per time period, or speed, calculated as L/T

Wave Requirements

• Waves need a medium (water, rope) and a generating force (wind, hand)
• Generated waves carry energy through the medium

Wave Speed and Behavior

• Wave properties help determine wave speed and behavior in shallow or deep water
• As a crest passes, water particles move backward and upward
• As a trough passes, particles move forward and downward
• Water particles exhibit forward circular motion when orbiting
• Energy passes through the water, but there is negligible net movement

Wave Distinctions

• In open water, away from the coast, water particles have orbital motion
• Orbital motion decreases with depth
• Water remains the medium for wave energy
• Water particle orbits diminish with depth
• Orbit diameter correlates to wave height at the surface
• Orbits disappear below the wave base

Deep Water Waves

• Occur when water depth exceeds half the wavelength
• Waves don't interact with the ocean bottom
• Celerity depends only on wavelength
• Period equals 1.56/c, where c is the celerity or speed in meters/second
• Longer wavelengths travel faster

Shallow Water Waves

• Water depth is much less than half the wavelength
• Waves interact with the bottom
• Depth determines speed
• Celerity is measured in meters per second
• Waves travel slower in shallower depth

Shoaling Waves

• Initial wave conditions in seas start chaotic with all wavelength sizes mixed in
• Long wavelength waves sort faster and move ahead
• Waves become swells sorted by wavelength with longer waves ahead of shorter
• Complex swells are from varying wavelengths
• Wave groups have similar wavelengths, originating from long distances

Wave Behavior as they Shoal

• Dispersion sorts waves by the time they reach shore
• Longest waves arrive first, short waves last
• Shoaling waves approach the shore, and deep-water waves become shallow-water waves
• As waves enter shallow water:
• Speed and wavelength decrease
• Height and steepness increase
• Period stays the same
• Orbitals flatten and become elliptical
• Waves break, and energy transforms into kinetic and potential energy, and friction

Wave Generation and Restoration

• Waves are classified by generating and restoring forces
• Generating forces add energy to the water such as wind, atmospheric pressure changes, and seafloor faulting
• Restoring forces return water to its undisturbed state like surface tension and gravity

Roughness of the Sea

• Wind-driven waves and sea state need high wind speed, duration, and long fetch
• Sea state develops through wind speed, fetch, and duration
• Strong winds over time generate the largest waves
• Beaufort scale (0-12): relates wind speed to sea conditions

Sea State Maximums

• Fully developed sea occurs with increasing wind
• Water forms whitecaps that start to break
• Wind speed has limits, or bigger waves will not form

Wave Height and Wave Interference

• Significant wave height: average of the highest one-third of waves
• Wave interference occurs when multiple waves combine
• Two or more waves with different amplitudes, wavelengths, and speeds combine to produce wave packets with varying energy.
• Constructive interference: crests/troughs align creating bigger waves
• Destructive interference: crests line up with troughs creating smaller waves

Rogue Waves

• Generated by means of constructive interference
• Are unpredictable, and can be dangerous, particularly if overly-steeped
• Can be 3-4x larger than nearby waves.
• Appear and disappear quickly
• Especially hazardous to coastal ships
• Produced when strong currents and large wind driven waves collide
• Max height formula for a Rogue Wave (0.14 x L)

Seiche (or Saysh)

• Resonant oscillation in an enclosed basin
• A standing wave occurs in said basin when there's wind and atmospheric pressure change
• Water body has resonance frequency/period
• This resonance heightens with size
• It depends on shape and shoreline
• Has the following Geological, Meteorological and Oceanic causes
• Fault slide (Lake Tahoe), pressure change (Great Lakes/ Geneva), and tsunamis entering harbors (Hilo Hawaii)

Tsunamis

• May be catalyzed in enclosed basins if the period is a multiple
• Reflection and damage are greatest in bags and harbours

Wave Interference vs Resonance in Marine Hazards

• Relation between seiches, resonance and rogue waves for marine safety

Seiches (Resonance Based Hazard)

• Standing wave within enclosed bodies of water
• Causes: can be caused by: storms, earthquakes, pressure changes
• Resonance: amplification occurs when the disturbance matches the natural frequency
• This interference can result heavy flooding current and structural damage.

Rogue Waves (Wave Interference Hazard)

• Exceptionally larger ocean waves occurring suddenly
• Occur when smaller waves align in phase, to amplify the giant wave
• Dangerous to ships

Lecture 3

Tsunamis

• Caused by earthquakes (vertical, submarine fault motion)
• Vertical changes rapidly displace the ocean's water column
• Higher chance of fault in pacific basin

Characteristics

• Long wavelengths (200-400km)
• Rapid celerity (200m/s)
• Smaller height waves initially
• Long periods (10mins-1hr)
• Very flat steepness
• Average depth of 4500m
• Waves (10-30m+) crest as their coming to shore
• Water is both advancing and retreating causing violent results
• Water decreases from (200km to 20m) rapidly incoming with tide

Detection

Lecture 4

Detection and Monitoring of Tsunamis

• Can be caused by submarine earthquakes transferring powerful energy

Required Conditions on Tsunami Generation:

• Requires converging plates with vertical fault motion
• 2 plates slide past one another from rupture of the seafloor
• Tsunami is caused from large scale subduction
• 2 mantles touching in subduction zone push energy vertically outward to cause water pressure
• Earthquakes with vertical seafloor movement
• Ocean volcanoes dumping mass

Tsunami Detection

• Cascadian subduction zone prone to earthquakes
• DART which measures pressure change on sea floor
• Pacific warning centres for tsunami

Arrival

• Shallow waves are predictable in arrival
• Time is calculated from distance to celerity

Shoreline

• South BC is in area E
• LTE and wifi devices need phone alerts for natural warnings

If Tsunami is Imminent

• Heed warnings: Sirens and notifications combined with intuition from nature are first
• Move inland fast: If possible move to a upper level roof
• Help those in need and expect devastation for property
• Flooding will be extreme

Additional BC considerations:

• Coasts will experience inundation and high current around ports
• Floating debris will also pose a risk

Final: wave transformations

Wave Formation

1. Unstable for its wavelength
2. Oceans floors cause motion when trough slows crest
3. Energy is transformed into Surf energy, molecular friction, and erosion
4. Beaches have: gentle wave action, violent tube waves and surging hazardous waves
5. Wave action changes movement causes sediments in transport
6. Longshore drift moves sand
7. Erosion, shape, storms are also factors that affect land

Man Made Structures

• Unbalanced deposition and erosion are causes
• Groins trap sediments perpendicular to the shoreline
• Jetties lock harbors in place
• Breakwaters cause protection
• Tethered breakwaters dissipate energy
• Sea walls reflect and Magnify erosion

Storm Surges

During Hurricane:

• Resulting in waves above the surface of water
• Low pressue and wind are major amplified factor
• Last for a days with strong winds using US hurricane centre modelling and SLOSH
• winds close to water are highest due to rotation

Explore wave propagation, energy transport, and media. Learn about ocean wave formation from wind and geological activity. Understand essential wave properties such as crest, trough, wavelength, period, and frequency.