C v GEO-SCI 103 Lecture 13Outline of Current Lecture: Waves pages (66-68, 78-79, 230-233)I. Geologic Hazards: Earthquakes and TsunamisA. Geologic HazardsB. TsunamiII. The Great Earthquake and Tsunami of December 26, 2004A. Off West Coast of Northern SumatraIII. Deep Water Waves: Energy on the MoveA. WavesB. Deep Water WavesC. Intermediate and shallower wavesCurrent LectureI. Geologic Hazards: Volcanoes, Earthquakes and TsunamiA. Geologic Hazards: closely associated with convergent plate boundaries and active continental marginsa) Situation leading to loss of property or life that is triggered by a geologicprocess such as earthquakes or volcanoesb) Earthquakes cause violent shaking of the ground near the focus and cause saturated soils to lose their cohesive properties in a process called liquefaction c) Earthquakes can cause rapid horizontal and vertical displacement of theground along preexisting faults and fractures in the rock d) Communities in tropical regions with high volcanic terrain are vulnerable to earthquakes, heavy rainfall and mudslidesB. Tsunamia) Large waves that are generated by strong earthquakes associated with the subduction of oceanic crustb) Communities on pacific islands and around the rim of the pacific are at riskc) May also be generated by undersea landslides along over steepened slopes of the continental margin (Atlantic)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.d) Size of waves depends on magnitude of the earthquake and configuration of the coastlinee) Long wavelength waves and behave like shallow water wavesf) International Tsunami Warning System monitors earthquake activity around the world and issues warnings about potentially dangerous tsunamisC. How Tsunamis are Produceda) Subduction zone is locked and strain buildsb) Seafloor is depressed by pressure of overlying platec) Overriding plate is buckled upward due to straind) Catastrophic release of strain causes major earthquakee) Seafloor rebounds rapidly as strain is removed and rapid uplift of seafloor causes displacement of large volume of seawater II. The Great Earthquake and Tsunami of December 26, 2004A. Off West Coast of Northern Sumatra a) Largest earthquake on Earth in over 40 yearsb) Magnitude of .9c) Caused by the release of a buildup of strain that had accumulated over many years by the slow motion collision of the Indian and Burma platesd) 30 minutes after the earthquake this wave appeared as a massive tsunami, up to 30 meters in some localities e) death toll of 300,000. 1.5 million left homeless because no networks existed in the Indian Ocean to warn people III. Deep Water Waves: Energy on the Move A. Wavesa) Represent the transmission of energy, not mass, along the interface between fluids of differing densityb) Wind waves1. Produced by the day to day changes in weather, particularly storms in contrast to the prevailing winds, which impart momentum to the upper water masses and drive ocean currents2. Wind blows across the ocean surface, ripples form in response to friction of wind, and waves reach equilibrium between the force of friction building them up and the force of gravity attempting to restore them c) Capillary Waves1. Waves start when the friction of the wind blowing across the sea surface forms small ripples (<1 cm)d) Equilibrium or Gravity Waves1. The frictional forces of the wind blowing over the water causes the ripples to become higher until they achieve equilibrium between the force of wind (which causes the water to mound up) and the force of gravity (which pulls the water back down to sea surface)2. Height to length ratio up to 1/7B. Deep Water Wavesa) The water molecules move in an orbital (circular) motion within the water column b) As the wave crest passes a point, the water moves upward, tracing part a circular path that is repeated c) The water travels in ever smaller circles until the effects of the wind energy disappear at a depth of one half the wavelength d) Also have a velocity called (celerity) that is a function of the wavelength so if you know the size of the wave, you can calculate how fast it is movinge) When the height of the wave is greater than 1/7 of its wavelength, the wave will break forming whitecaps on the open oceanf) Wave period: (T) the time it takes two successive crests to pass a fixed point g) In deep water, wave velocity or celerity (C) is controlled by wave period (t) and wavelength (L): C=L/TIV. Waves in Shallower Waters:A. Storm Waves (Sea): chaotic mixture of wavesa) Wave size depends on 1. Wind speed2. Duration of storm3. Fetch (distance over which the storm winds blow) b) Fully developed sea = maximum wave size for the storm conditionsB. Swell: regular in shape, sorted by wavelengtha) Beyond the seab) Little loss of energyc) More regular in shaped) Dispersion of wave trains (longer L waves= faster)e) Inference patterns form swell generated in other storms)C. Shallower Watera) Orbital motion of wave energy encounters friction with seafloorb) Waves slow down and pile up1. Decrease in wavelength (L2. Increase in wave height (H3. Decrease in celerity (L/T)4. Waves break (H/L=1/7)5. Incoming waves set up long shore currents parallel to shore D. Timelinea) Storms: energy inb) Swell: waves move away from the sea that generated them, this energy can travel across an entire ocean basin like the pacific oceanc) Surf: energy out E. Intermediate and Shallow Water Wavesa) As waves approach the shore, the orbital wave motion eventually encounters the seafloorb) The orbits become increasingly compressed due to the wave dragging on the seafloorc) The wave slows down (C decreases) due to frictional drag and the wavelength (L) decreases whereas (T) remains the samed) The waves grow in height (H/L) increases and eventually topple overe) Incoming Waves set up longshore currents and turbulence on seafloor causing sediments to be lifted into suspensionf) Sediment is transported back and forth along the shore as Longshore