Introduction

From the observations of Lt. Pelham aboard the Each of the half-hour video episodes is accompa- H.M.S. Challenger to the mapping of by satel- nied by a complementary lesson containing the fol- lites and undersea vehicles, the study of the is lowing features to help you master your study of as rich and dynamic as the ocean itself. The Endless : Voyage will bring you face to face with exotic deni- — An Overview summarizes each lesson’s main zens of the deep and the peculiarities of their watery topics. world. It will take you on virtual field trips to lead- ing research institutions fromWoods Hole, Massa- — Learning Objectives identify the major concepts, chusetts to La Jolla, . It will introduce you ideas, and factual data that you should recall and to scientists and academicians involved in the sci- understand after viewing the video and reading ence and study of oceanography in a wide range of the required selections from the text. Many test disciplines who share their ideas and insights with questions are derived from these objectives. you. — Assignments that link the video lesson with This guide is one part of the total package avail- related sections of the text. able to you when you embark upon the 26 half-hour videos that comprise The Endless Voyage. Each video —Video Focus Points help you follow and analyze episode will introduce you to academicians, information in the video and integrate the infor- researchers, physical oceanographers, chemists, mation with your readings. marine biologists, specialists, geologists, — Text Focus Points are intended to guide your and a host of others—people whose contributions reading of the selections for each assignment. are helping to interpret current understanding of the Earth’s ocean and shape the our environmental — Key Terms and Concepts help you to focus on the future. words and ideas important to understanding the These video episodes, in conjunction with the language of oceanography as you work through guidance of your instructor, are closely integrated each lesson. with Tom Garrison’s text, Oceanography: An Invita- — A Self Test enables you to check your under- tion to Marine Science. The fifth edition of this popu- standing of the material in the video and text lar text provides a richly illustrated foundation of assignments. information upon which to base your study. An interactive web component enhances independent — Supplemental Activities provide opportunities learning. for further examination of the issues raised by the video and readings in the text.

v Lesson 13

Surf’s Up

Overview

Do waves conjure an image of lazy sunsets and clear mental image of this orbital activity to set the the gentle slap of water on the sand? Or maybe stage for understanding the forms and behaviors the roar of water littered with surfers? Waves can of the various types of wind waves. The diagrams range from soothing to destructive. In its broadest found on pages 230 and 231 of your text will help. definition, the term wave describes a disturbance Ocean waves are classified and named accord- caused by the movement of energy from a source, ing to the disturbing forces that cause them, and through a medium—solid, liquid, or gas. As that the restoring forces, or surface tension and grav- energy, or disturbing force, travels, it affects the ity, that attempt to restore the surface to smooth- medium in specific ways. The focus of this lesson ness. Wind is a major disturbing force, but is how ocean water is affected by a particular type , landslides, erupting volcanoes, and of energy; namely, the wind. can also cause waves. Waves can occur in Ocean waves seem like a moving ridge of any ocean, but are most common around the equa- water that can be ridden to shore. By definition, tor and in the Southern Hemisphere, where most however, a wave is a moving ridge of energy, not storm energy originates. Large waves originating water. Look at Figure 10.1 on page 230 in your in these areas tend to move northward, affecting text, in which a seagull sitting on the water’s sur- the ocean and shorelines in the Northern Hemi- face stays in essentially the same lateral position sphere. but is moved vertically as the forward-moving In order to discuss and understand energy changes the wave form, or shape, from formation and behavior, there are a number of crests to troughs to crests. When energy contacts descriptive terms to be learned. Wave shape con- the surface as wind, some of it is transferred to sists of the crest, or high point, and trough, or low the water beneath the surface, causing the water point. The period of a wave is its travel time molecules comprising the wave form to move. expressed in seconds and measured based on the These tend to form a circular, or orbital, pattern as time it takes successive wave crests to pass a fixed the energy passes, but the water itself does not point. Wave size refers to its height and length. progress forward. This orbital wave concept Wavelength is measured by the distance applies to most of the more common types of between adjacent crests or adjacent troughs. The waves. speed of a wave is based on the ratio of the length The orbital motion of the water continues of the wave to its period. It is ultimately controlled beneath the surface, but the diameter of the orbit by , wavelength, and water depth. As a gen- is controlled by the depth of the water, rapidly eral rule, the longer the wavelength is, the faster diminishing when the depth of the water is less the wave energy will move through the water. than half of the wavelength. Most ocean waves Height is an important characteristic of wind have moderate wavelengths, so the circular distur- waves, and is measured from the trough to a line bance that propagates the wave affects only the connecting the two adjacent crests. Moderately uppermost water mass. It is important to have a sized waves usually have about a 1:7 ratio of wave

93 94 The Endless Voyage height to length. Waves with a ratio higher than Not all waves are surface waves; subsurface this will often break at sea, dissipating their internal waves may form where water of different energy as whitecaps or combers. The highest wave density masses meet. You may recall that most accurately measured and recorded to date was 34 surface winds in the tropical Pacific, such as trade meters (112 feet). winds, move from east to west, but that at irregu- Wind waves begin as small capillary waves, lar intervals they can reverse direction and move when some wind energy is transferred from the from west to east. This is called the Southern atmosphere to the sea surface. If the wind contin- Oscillation, and it causes in the ues and grows stronger, the orbital motion gains area to change direction, too. Instead of flowing up momentum, while the surface tension and grav- and away from the equator it moves down and ity—the restoring forces—try to flatten them out, toward it. The warm water of the upper layer of creating a larger wave called a . the Pacific downwells into the lower layer, result- Deep-water waves are those that move ing in an oscillation where those two density- through water that is deeper than one-half their different layers meet. This oscillation forms an wavelength; shallow-water waves are found at the base of the pycnocline, espe- where the water is less than one-twentieth of the cially at the bottom of a steep . wavelength. Deep-water waves can become larger Internal waves are also important in trans- as the wind continues to blow, forming into a cha- porting and mixing nutrients with surface waters, otic mix of waves of different lengths, called a sea. affecting both midwater and coastal planktonic These storm waves tend to sort themselves out organisms. Although deep-ocean internal waves into groups with similar lengths and speeds, set- are less well known than those along the coasts, tling into a smooth surface undulation called space shuttle and TOPEX/Poseidon satellite data , which may develop into progressive groups have recently documented their existence and called wave trains. Wave trains coming from dif- basic behaviors. ferent directions sometimes meet in an interaction Since they are such a fundamental component known as interference. It is called destructive of the oceanic system, waves have been observed interference if they counteract each other and con- and studied since the early voyagers. Wave study structive interference if they reinforce each other. became even more important in the mid-1940s If high crests from different wave trains meet, a when amphibious landings on the coasts of —one that is higher than is theoreti- Europe were being planned during World War II. cally possible—may form. Rogue waves can also Since then significant progress has been made in form when a wind wave meets a swift current. the effort to describe, monitor, and predict wave As a deep-water wave approaches a shoreline formation and propagation using a number of it will eventually “feel” the bottom, which initiates highly innovative techniques and devices. One a series of events that change the form and speed such device, called a pressure sensor, is mounted of the wave, eventually forming surf as the wave on the sea floor and actually records dissipates its water and energy on the beach. as indicated by the weight of the water passing When gravity moves that water back down the over it. Fixed electric gauges are used to record beach, it can form swift, outward-moving rip cur- changing wave heights; and an array of wave rents, which can be dangerous to swimmers. buoys is in place along the West Coast of the Most waves fall into the category of progres- United States measuring wave height and direc- sive waves; so named because the wave forms tion and sending the data to computers at the move forward. When a wave line approaches land, Scripps Institution of Oceanography in California. its configuration is affected by the geography of Satellite altimeters sense changes in the sea sur- the local shoreline. Most waves move toward face and transmit the data to oceanographic insti- shore at an angle, causing the wave line to bend, or tutions or computers on ships at sea. refract. If the wave line encounters an obstacle While adding to knowledge of the basic sci- such as a rock or breakwater, it is interrupted or ence and physics of wave formation and propaga- diffracted. When a wave series enters a bay or har- tion, these instruments also track the dispersal of bor the energy is reflected away from the land, natural nutrients, pollutants such as oil and other causing a , or water mass that oscil- chemicals, and the biology of phytoplankton as it lates vertically without progressing. affects the global carbon budget. Lesson 13: Surf’s Up 95

Focus Your Learning

Learning Objectives Video Focus Points

After completing this unit you should be able to Review these points before watching the video do the following: assignment for this lesson to help you focus on key issues. 1. Recognize that wind waves are formed and propagated by transmission of wind energy to — Wind waves are best known for their effect on the sea surface, and that it is the energy that shorelines and ships at sea. moves as a wave, not the water. — Wind waves are characterized by their height, 2. Understand that this energy causes water to length, and period. move in closed circular paths (orbits), which — A wind wave is formed when moving air con- carry the energy forward as a progressive wave tacts the ocean surface. Water molecules begin form. an orbital motion and the wind energy is 3. Explain how waves are classified and named moved forward, but the water stays in essen- based on the strength and character of the tially the same place. forces that affect them. — When waves encounter a shoreline they 4. Describe the relationship between wave length change shape and transfer their energy onto and wave speed. the land. Rip currents can form as the water retreats back down the beach to the sea. 5. Discuss the terminology used in describing wind waves and their effects—size and shape, — Waves impacting continental margins can crest-and-trough, rogue waves, surf, sea, and cause erosion and major relocation of beach period. components such as sand. 6. Describe the chronological sequence of events — At sea, large wind waves can impact offshore that occur from the time a deep-water wave structures, such as oil rigs and ships, in the begins to approach a shore until it breaks as form of very large, isolated rogue waves. surf. Waves of different periods and lengths can also come together and reinforce each other into 7. List and briefly discuss the behaviors—refrac- larger waves. tion, diffraction, reflection—exhibited by waves as they encounter different types of — Internal waves are formed at the subsurface shorelines. boundary of two density-different subsurface water masses, and behave much like surface 8. Recognize the role of wave study in oceanogra- waves. phy, its importance in World War II, and the technologies now in use to study waves. — The study of waves became important in the 1940s, during the planning of amphibious landings in World War II. Assignments — A number of innovative techniques and This lesson is based on information in the follow- devices are now used to study wave formation ing text and video assignments. The key terms, and propagation—pressure sensors, electric focus points, and practice test are intended to help gauges, buoy arrays, and satellite altimeters. ensure mastery of the material presented in this — Wave activity and its effect on ocean circula- unit of study. tion is important in studying and tracking Text: Chapter 10, “Waves,” pages 228–244 nutrients, pollutants, plankton distribution, and Earth’s carbon budget. Video: Episode 13, “Surf’s Up” 96 The Endless Voyage Text Focus Points — When wind waves encounter shallow water as they approach shore, a sequence of events Review these points before reading the text begins that leads to their eventual breaking on assignment for this lesson to help you focus on shore, forming surf. key issues. — Wave lines usually approach a shoreline at an — Wind waves form as the energy of moving air angle, refracting from their original direction. is transferred to the sea surface, forming small Diffraction can occur when a wave line moves capillary waves in which the water begins to around an obstacle, such as a rock or break- move in an orbital pattern. Energy is moved water; wave reflection happens when a wave forward, but the water particles remain essen- train enters a or bay and is reformed tially in the same place. At the same time, sur- into a non-progressive standing wave. face tension and gravity (restoring forces) act — Internal waves may form at the boundaries of to return the sea surface back to smoothness. density-different subsurface water masses, — Ocean waves are characterized and described usually at the steep thermocline seen at the bot- according to their height, length, and period. tom of the pycnocline. Internal waves may move rapidly, and have many of the same char- — Shallow-water waves move in depths shal- acteristics and behaviors as surface waves. lower than one-twentieth of their wavelength; deep-water waves move in water deeper than half of their wavelength. Only wind can form Key Terms and Concepts deep-water waves; shallow-water waves can also form from earthquakes, volcanoes, land- A thorough understanding of these terms and slides, and tides. concepts will help you to master this lesson. — Wavelength determines the speed with which a Cgd= . Calculation for the speed of shallow- wave can move. The longer the wavelength the water waves. C represents speed (celerity), g is greater the speed. acceleration due to gravity, d is the depth of water in meters. — If the wind continues to blow over water deeper than half the wavelength, waves can C=L/T. Calculation for the speed of deep-water become larger and more erratic, forming a cha- waves. C represents speed (celerity), L is the otic surface called sea. wavelength, T is time. — Storm waves sort themselves out into groups Capillary wave. A tiny wave with a wavelength of with similar lengths and speeds, resulting in less than 1.73 centimeters (0.68 inch), whose the smooth, undulating surface called swell, restoring force is surface tension; the first type of which can organize further into wave trains. wave to form when wind blows. — The growth and movement of wind waves is CDip program. Coastal Data Information Program affected by wind strength and duration, and monitored by the Scripps Institution of Oceanog- the uninterrupted distance over which it can raphy in California and consisting of a wave buoy move, called fetch. array located on the West coast of the United States that records wave height and direction. — The ratio of wave height to length, about 1:7, is called the wave steepness. If this ratio is Constructive interference. The addition of wave exceeded and the wave grows high, the excess energy as waves interact, producing larger waves. energy will cause it to break at the crest, form- Deep-water wave. A wave in water deeper than ing whitecaps or combers. one-half its wavelength. — When wave trains of different speeds meet, Destructive interference. The reduction of wave they may either cancel each other out (destruc- energy as waves interact, producing smaller tive interference) or reinforce each other to waves. become larger waves (constructive interfer- ence). Huge, isolated rogue waves may form in Fetch. The uninterrupted distance over which this way. Rogue-type waves may also form wind blows without a significant change in direc- when wind waves meet strong, swift currents. tion, a factor in wind wave development. Lesson 13: Surf’s Up 97

Free wave. A progressive wave free of the forces Transitional wave. A wave moving through water that formed it. deeper than one-twentieth but shallower than half its wavelength. Gravity wave. A wave with wavelength greater than 1.73 centimeters (0.68 inch), whose restor- Wave. Disturbance caused by the movement of ing forces are gravity and momentum. energy through a medium. Interference. Addition or subtraction of wave Wave crest. Highest part of a progressive wave energy as waves interact. above the average water level. Internal wave. Progressive wave occurring at the Wave diffraction. Movement of waves around boundary between liquids of different densities. obstacles. Orbit. In ocean waves, the circular pattern of Wave frequency. The number of waves passing a water molecule movement at the air-sea interface. fixed point per second. Orbital motion contrasts with the side-to-side or Wave height. Vertical distance between a wave back-and-forth motion of pure transverse or longi- trough and adjacent wave crests. tudinal waves. Wave period. The time in seconds that it takes for Orbital wave. A progressive wave in which parti- successive wave crests to pass a fixed point. cles of the medium move in closed circles. Wave reflection. The reflection of progressive Pressure sensor. A device that is mounted on the waves by a vertical barrier. Reflection occurs with sea floor, designed to weigh the water that passes little loss of energy. over it, as a measure of wave height. Wave refraction. Slowing and bending of progres- Progressive wave. A wave of moving energy in sive waves in shallow water. which the wave form moves in one direction along the surface of the transmission medium. Wave size. The height and length of a wave. Restoring force. The dominant force acting to Wave speed. How fast the energy of a progressive return water to flatness after formation of a wave. wave is moving forward. Calculation differs for deep-water and shallow-water waves; see formu- . A strong, fast current formed by the las at the beginning of this list, and in the text. seaward return flow of surf. Sometimes called, erroneously, rip . Wave steepness. Height-to-wavelength ratio of a wave. Theoretical maximum steepness of deep- Rogue wave. A single wave crest much higher water waves is 1:7. than usual, caused by constructive interference. Wave train. A group of waves of similar wave- Sea. A term used to describe simultaneous wind length and period moving in the same direction waves of many wavelengths, forming a chaotic across the ocean surface. ocean surface. Sea is common in an area of wind wave origin. Wave trough. The valley between wave crests below the average water level in progressive Shallow-water wave. A wave in water shallower waves. than one-twentieth its wavelength. Wavelength. The horizontal distance between Standing wave. A wave in which water oscillates two successive wave crests (or troughs) in a pro- without causing progressive wave forward move- gressive wave. ment. There is no net transmission of energy in a standing wave. Whitecaps/combers. A wind wave breaking at sea and releasing its energy at the crest. Surf. A term used to define the confused mass of agitated water rushing shoreward during and Wind duration. The length of time the wind blows after a wind wave breaks. over the ocean surface, a factor in wind wave development. Swell. Mature wind waves of one wavelength that form orderly undulations of the ocean surface. Wind strength. Average speed of the wind, a fac- tor in wind wave development. 98 The Endless Voyage

Wind wave. Gravity wave formed by transfer of wind energy into water.

Test Your Learning

After working through these questions, check 6. Three factors directly affect the growth of your answers against the key at the end of this wind waves—wind strength, wind duration, book. If you answered any of the questions incor- and: rectly, review the relevant sections of the text and a. cohesion video episode. b. c. fetch d. group velocity Multiple Choice 7. The largest wave accurately measured and 1. Wavelength is defined as: recorded was ______feet high. a. the horizontal distance a wave travels in a. 237 one second b. 112 b. the horizontal distance between successive c. 98 crests (or troughs) d. none of the above c. the horizontal distance a wave particle 8. Rogue waves are usually the result of: travels during a 30-second interval a. destructive interference d. none of the above b. surf break 2. The basic concept of a wave is that of a c. constructive interference ______caused by the movement of ______d. wave diffraction through a ______. 9. A deep-water wave is defined as a wave mov- a. crest / water / sea ing through water: b. disturbance / energy / medium a. more than 100 km deep c. particle / gravity / liquid b. in a fully-developed sea d. surface / wind / water basin c. deeper than half of its height 3. Rip currents are the result of: d. deeper than half of its length a. breaking waves returning to the sea 10.Waves forming between layers of fluids of dif- b. longshore currents caused by wave ferent densities are called: diffraction a. pycnocline rhythms c. energy expended against steep vertical b. transitional waves shorelines c. internal waves d. all of the above d. all of the above 4. Surface tension/cohesion is the main ______11.When the maximum wave size theoretically for capillary waves. possible for a wind of a specific strength, dura- a. disturbing force tion, and fetch is reached, this is called a: b. waveform a. seiche c. restoring force b. rogue wave d. dispersing force c. fully-developed sea 5. Waves of different periods and wavelengths, d. wave train combining and moving in different directions, is called a. dispersion b. wave train c. swell d. sea Lesson 13: Surf’s Up 99

12.When a shoreward-bound wave is propagated 2. Imagine a large progressive wave train around an obstacle such as a rock or break- approaching a wide harbor mouth straight-on, water, it is said to be: entering the harbor and moving through it, a. reconstructed assuming there are no major obstructions to b. diffracted the rear of the harbor and impacting the sea- c. refracted wall at the back. If conditions were right, the d. reflected progressive wave train could be re-formed into a standing wave. Describe the sequence of events. Short Answer 3. Describe and document the sequence of events 1. Discuss the so-called rogue wave—what is it, occurring as a deep-water wave approaches a how is it formed, how is it different from other shoreline, from the first encounter with the wave forms and patterns, and what are some bottom until it breaks as surf, and how the con- famous “rogue wave encounters.” tours and characteristics of the nearshore bot- tom determine the nature of the .

Supplemental Activities

1. Use the Internet and local libraries to docu- If you wish to construct such a device, it is ment and expand upon ’s open- best done using a clear bottle, either round or ing statement in the video – “It became clear rectangular. A round bottle, such as a liter early in World War II that amphibious land- wine bottle, will work, provided it has a ings would have to be concerned about the screw-top that can be tightened. If you can intensity of wave action on the beaches.” find a small, square bottle, such as the type used for some types of cooking sauces, you 2. Contact some surfers (body or board) and/or will get a little better representation of the look in surfing publications, and learn the basic interacting fluids. Rinse out the bottle and jargon/terminology they use in describing soak off the label, then fill it with water and wave activity and how they interact with it to lay it on its side, to see if it is leak-tight. If it pursue their sport. Then assemble a “guide” for leaks, you can seal it with tape when it is the non-surfer, combining the descriptive jar- filled. Half-fill the bottle with plain water, add gon with the actual scientific explanations of a few drops of food coloring, and shake to mix. the wave phenomena. Blue is the most appropriate color, but any 3. Page 244 of your text mentions “Desktop- color will do to show the water mass bound- ocean” devices, which illustrate some of the ary. Then, very slowly and carefully (so as not characteristics of internal waves. If you already to create air bubbles), fill the bottle to the very own one of these devices, or can purchase one, top (almost overflowing) with mineral oil use it to simulate what happens at the bottom (available at any pharmacy). Screw the lid on of the pycnocline when liquids of different tight, tape it if necessary, and tilt the bottle densities meet. Following the explanation in slowly and gently. Note, describe, and docu- the text under “Internal Waves,” document/ ment the various ways that the layers interact. describe/explain what happens as these fluids If you do this well, and the bottle is tightly interact, as it relates to the behavior of internal sealed, it may make a nice desk ornament. waves. 222 The Endless Voyage

– CFCs move easily from the atmosphere into – Wind waves from different storm systems the , where they dissolve and will have different characteristics, with spread into the ocean, like a dye. longer waves outrunning (and interfering – During the initial 40 years of their industrial with) shorter ones. use (l930s to l970s) their atmospheric con- – Destructive interference can have a cancel- centration increased rapidly, leading to lation effect on the participants, whereas many of them being banned because of their constructive interference can result in potential to damage Earth’s ozone layer. waves much larger than the individual par- – The usefulness of these chemicals as tracers, ticipants. to study ocean circulation, is based on the – Waves of many heights and lengths can con- fact that the history of their production, use, verge on an area from different directions, and eventual contact with the ocean through meeting to form a rare, huge wave called a the atmosphere, can be documented. rogue wave, often much larger than is theo- – CFC-11 and CFC-12 were two of the first to retically possible. Such a wave could be 3–4 be manufactured and used. By measuring times the theoretical average. the concentration of these two CFCs in sea- – In 1942 the Queen Mary was struck broad- water, and comparing their ratios with the side by a rogue wave off , causing it ratios of their known changes in the atmo- to tilt more than 45 degrees. sphere, one can estimate the last time that – In l912 a smaller Cunard liner, the Carma- water mass was in contact with the atmo- nia, loaded with tourists, was struck by a sphere. rogue wave, sending it into a series of rolls – The equipment and instrumentation for over 50 degrees and causing much damage. doing this is quite complex, and is presently A similar wave hit the Queen Elizabeth II, in being built, tested, and modified, with a lot 1996, frightening passengers and crew but of sea trials. One of the main requirements is causing no injuries or damage. that the sampling and analytic apparatus 2. Imagine a large progressive wave train must be absolutely airtight, to prevent any approaching a wide harbor mouth straight-on, ambient-air contamination. entering the harbor and moving through it, – So far, scientists have been able to date the assuming there are no major obstructions, to formation of some water masses as far back the rear of the harbor and impacting the sea- as the l920s, and up to the present. wall at the back. If conditions were right, the progressive wave train could be re-formed into Lesson 13: Surf’s Up a standing wave. Describe the sequence of events. 1. b page 229, Video – The progressive wave train encounters the 2. b page 229 harbor mouth straight on, and most, or all of 3. a Video its energy passes into the basin of the har- 4. c page 231 bor. 5. d page 234, Video – Assuming no major obstructions, the lead 6. c page 236 wave will move through the harbor, fol- 7. b page 237, Video lowed by the successive waves in the train, 8. c page 240, Video still acting as a progressive wave. 9. d page 232 – When the lead wave hits the seawall at the 10. c page 244, Video rear of the harbor, it will be reflected back 11. c page 236 and move away from the seawall in the 12. b page 242 direction in which it entered. – Meanwhile, the other waves in the train are Short Answer approaching, and the lead wave, being the 1. Discuss the so-called rogue wave—what is it, first to be reflected back, will impact the fol- how is it formed, how is it different from other lowing waves and cause constructive inter- wave forms and patterns, what are some ference in the form of vertical oscillations famous rogue wave encounters. called a standing wave. – Independent wave trains exist simulta- – These waves do not progress but appear as neously in the ocean most of the time. alternating crests and troughs, and because Answer Key 223

their interference is constructive they can coral, or if there is floating seaweed or ice in actually become larger than the original the wave’s path. wave. – If the bottom is deep until it meets a vertical – This energy will eventually dissipate, shoreline or cliff face, the wave may not go because in reality there are no basins or har- through this series of steps leading to the bors with geometrically square sides, so the classic break, but will lose its energy as it waves would assume angles of reflection off crashed into the cliff, sending water both the basin walls and the standing wave pat- downward and skyward. tern would disappear. 3. Describe and document the sequence of events Lesson 14: Look Out Below occurring as a deep-water wave approaches a shoreline; from the first encounter with the 1. d page 245 bottom until it breaks as surf, and how the con- 2. a page 247 tours and characteristics of the nearshore bot- 3. b page 247 tom determine the nature of the breaking 4. c pages 245, 247 wave. 5. d Video – A deep-water wind wave moves through 6. c page 250, Video water deeper than half its wavelength. 7. b page 250 – As the wave approaches a shoreline it 8. d Video encounters water shallower than half its 9. a page 249 wavelength but still deeper than 1/20 of its 10. b page 250 original length. This is a transitional wave, 11. c Video which then continues to move shoreward, 12. b Video into water less than 1/20 of its original Short Answer wavelength, to become a true shallow-water wave. 1. Describe, in some detail, NOAA’s National – Here the wave contacts, or “feels” the bot- Tsunami Hazard Mitigation Program. tom, and its circular orbit pattern is inter- – The overall purpose of the Program is to rupted, with the part near the bottom reduce hazards due to tsunami impacts, flattening into an ellipse and moving more based on a three-part approach. slowly due to friction with the bottom. – One element of the Program deals with haz- – But the wave still retains most of its for- ard assessment—on a local/community ward-moving energy, concentrated in the basis, the recognition and analysis of both upper part, causing the formerly rounded the geographical and population aspects of wave crests to peak. at-risk areas. This can include consideration – The following waves, not having felt the bot- of past tsunami threats or events, and their tom yet, continue toward shore at their orig- impacts on that community, as well as inal speed. attempting to model/predict reactions to – As it peaks, the ratio of 1:7 height to length future events. is approached. – Another component of the program consid- – As the wave form is modified, the water is ers hazard mitigation; basically a prepara- actually moving faster than the wave form tion/evacuation plan. Both state and federal and as the crest moves ahead of its slower- agencies, including FEMA, are involved. moving base it breaks, when at the ratio of Emergency facilities, shelters, food stocks, about 3:4 height to length. etc., are documented, as are areas at espe- – The break sends this turbulent mass of cially high risk of inundation. water onto the beach as surf, and its wind- – In areas at very high risk like , the generated energy is released as random mitigation part of the program also gets movement, heat, and sound. involved with building codes and the actual – If the shoreline slopes upward gradually, redesigning of shoreside structures to mini- waves lose their strength because their mize damage in the event of a tsunami. lower orbit is in contact with the bottom – The third element of NOAA’s Program is a longer. This loss of energy can be further detection/prediction/warning system, enhanced if the bottom is loose gravel or designed to lessen property damage and loss