DOCSLIB.ORG

What Are Waves? What Causes Waves? Tidal Waves Tsunamis Wind Generated Waves Swell

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
What Are Waves? What Causes Waves? Tidal Waves Tsunamis Wind Generated Waves Swell What are waves? toward the moon. An equal bulge in the surface of Tsunamis The strength of the wind the ocean occurs on the side of the earth opposite Water waves are a manifestation of energy moving of the moon due to the centrifugal force generated Often misnamed tidal waves, Tsunamis are long through the ocean. In their simplest form, waves are by the earth’s rotation. In between the 2 bulges the period waves that originate when a strong The amount of time the wind blows sinusoidal in shape. The high water levels are the ocean surface is depressed due to the movement of earthquake or landslide occurs under the ocean. wave crests and the low water levels are the wave water toward the bulges. The motion of the earth sends a strong impulse of The distance (called fetch) over which the troughs. The vertical distance between a crest and energy into the water generating surface waves wind blows in a straight line across the trough is the wave height H. The distance between with open ocean heights of less than 2 feet but ocean two crests or troughs is the wave length L and the with wave lengths of over 100 miles and wave time it take for two crests or troughs to pass the speeds approaching 500 miles per hour! same point is the wave period T. The velocity, C, at which a wave moves through the ocean is related to the ratio of its wave length to wave period: C = L/T The wave length is proportional to the square of the wave period, L ~ T2 so longer waves move As the moon rotates around the earth, the bulges faster than move as well resulting in 2 high and 2 low tides per shorter ones. day at most locations on the coast with a tidal period The amount of of approximately 12 ½ hours. energy, E, in the wave is a The exact number of the tides is dependent on the The stronger the wind and the longer it blows function of the shape of the ocean bottom along the coast. This can across the fetch, the larger the sea will become. A wave height and have a significant effect on the height and period of As a tsunami approaches the coast, the wave fully developed sea occurs when the waves is proportional to: the tide along the coast as seen in the tidal curves interacts with the shallow bottom. Because of their reach the maximum size possible for a specific E ~ 1/8 H2. for the east coast. long wave lengths tsunamis rarely break along the wind, duration and fetch. coast. Instead the water runs up along the shore Some coastal geometries have the right size and similar to the tide. In some cases where the coast shape to produce amplified tides that result in very Swell is close to the center of the earthquake the water large tidal ranges. Some locations in the Bay of surge associated with a tsunami can reach What causes waves? Fundy, Nova Scotia experience a tidal range of over When waves travel out of the region of strong elevations over 100 feet high. Damage to winds, they become sorted as the longer waves 40 ft! lighthouses over 150 feet above sea level has A disturbing force is necessary to create waves on travel out from the storm faster than the shorter the ocean surface. The type of disturbing force been documented during tsunami events. waves. This results in waves of similar In shallow coastal regions, the currents generated determines the characteristics of the generated by the incoming tide can produce Tidal Bores, characteristics moving together across the ocean waves. The 3 main wave generation forces in order visible waves that move inland from the coast. Wind Generated Waves in groups. Waves lose very little energy as they of decreasing wave period are: propagate across the deep ocean. Removed from Wind blowing across the surface of the ocean the influence of the wind the wave crests of the transfers energy into the water. Initially, light winds swell become rounded. Gravitational Attraction of Moon and Sun generate small Ripples called capillary waves on producesTides the water surface. Earthquakes and Underwater Landslides If the wind increases, the added roughness generate Tsunami created by the capillary waves increases the rate of energy transfer and waves begin to form on the Wind Stress over the ocean generates ocean surface. Wind Waves In the the region where wind is blowing across the ocean surface and waves are being generated, Tidal Waves the sea surface is characterized by steep waves with many different lengths moving randomly in Tides are generated by the gravitational attraction of the direction of the wind. This condition is referred the earth, moon and sun. On the side of the earth to as sea. How large the waves get is dependent closest to the moon, the ocean surface bulges out on3factors: Wave Shoaling and Refraction (Cartoons courtesy of Office of Naval Research) When waves enter shallow water (water depths On beaches with equal to ½ the wave length) friction generated by gentle slopes, the the seabed begins to slow the motion of the waves. wave crest breaks If part of the wave is still in deep water, the slower first and the white portion of the wave will bend toward the coast. water spills down This process is called wave refraction. the face of the wave. On very steep COASTAL PROCESSES beaches, the does not break at all but COOPERATIVE EXTENSION surges up the beach instead. Current Wave Conditions photo by Jon Sullivan For real-time information about ocean wave conditions see the following web pages: This factual brochure was prepared through SSuurrff’’ss UUpp!! the Stevens – New Jersey Sea Grant Coastal Processes Cooperative Extension formed to As the bottom of the wave slows, the waves crest promote the sustainability and wise use of our becomes more peaked and the distance between coastal resources that provide the basis of a wave crests shortens. This process is referred to strong coastal economy. as wave shoaling. For additional information contact: Dr. Thomas Herrington Coastal Processes Specialist, Stevens Institute of Technology Castle Point on Hudson, Hoboken, NJ 07030 PH (201) 216-5320 FX (201) 216-8214 email:[email protected] or Photo courtesy of the NOAA Marine Prediction http://attila.stevens- Merchant Vessel in fully developed sea. tech.edu/%7Etherring/SeaGrant.html Wave Breaking When waves reach a critical wave height to length This publication was supported by the National Sea Grant ratio of 1/7, the wave will begin to break. In the surf College Program of the U.S. Department of Commerce’s photo by Jon Sullivan zone, this critical ratio generally occurs when the National Oceanic and Atmospheric Administration under NOAA Grant #NA16RG1047. The views expressed herein do wave height is ¾ of the water depth. There are 3 not necessarily reflect the views of any of these organizations. types of breakers that occur along the shore: NJSG-03-549. plunging, spilling and surging. The type of breaker depends on the slope of the seabed Compiled By: Dr. Thomas Herrington, Stevens Institute of Technology offshore of the beach. When waves go from deep Designed By: Jacqueline Harris, NJMSC water to shallow water quickly the bottom of the All About wave slows so quickly Photo courtesy of the Pacific Tsunami Museum that the crest of the wave plunges forward Surge associated with the 1946 tsunami that creating a tubing wave struck Hawaii. Notice height of white water along like those found in Waves tree trunks. Hawaii. .
Load more

Recommended publications
  • Wind-Caused Waves Misleads Us Energy Is Transferred to the Wave
    WAVES IN WATER is quite similar. Most waves are created by the frictional drag of wind blowing across the water surface. A wave begins as Tsunami can be the most overwhelming of all waves, but a tiny ripple. Once formed, the side of a ripple increases the their origins and behaviors differ from those of the every­ day waves we see at the seashore or lakeshore. The familiar surface area of water, allowing the wind to push the ripple into waves are caused by wind blowing over the water surface. a higher and higher wave. As a wave gets bigger, more wind Our experience with these wind-caused waves misleads us energy is transferred to the wave. How tall a wave becomes in understanding tsunami. Let us first understand everyday, depends on (1) the velocity of the wind, (2) the duration of wind-caused waves and then contrast them with tsunami. time the wind blows, (3) the length of water surface (fetch) the wind blows across, and (4) the consistency of wind direction. Once waves are formed, their energy pulses can travel thou­ Wind-Caused Waves sands of kilometers away from the winds that created them. Waves transfer energy away from some disturbance. Waves moving through a water mass cause water particles to rotate in WHY A WIND-BLOWN WAVE BREAKS place, similar to the passage of seismic waves (figure 8.5; see Waves undergo changes when they move into shallow water­ figure 3.18). You can feel the orbital motion within waves by water with depths less than one-half their wavelength.
    [Show full text]
  • Time and Tides in the Gulf of Maine a Dockside Dialogue Between Two Old Friends
    1 Time and Tides in the Gulf of Maine A dockside dialogue between two old friends by David A. Brooks It's impossible to visit Maine's coast and not notice the tides. The twice-daily rise and fall of sea level never fails to impress, especially downeast, toward the Canadian border, where the tidal range can exceed twenty feet. Proceeding northeastward into the Bay of Fundy, the range grows steadily larger, until at the head of the bay, "moon" tides of greater than fifty feet can leave ships wallowing in the mud, awaiting the water's return. My dockside companion, nodding impatiently, interrupts: Yes, yes, but why is this so? Why are the tides so large along the Maine coast, and why does the tidal range increase so dramatically northeastward? Well, my friend, before we address these important questions, we should review some basic facts about the tides. Here, let me sketch a few things that will remind you about our place in the sky. A quiet rumble, as if a dark cloud had suddenly passed overhead. Didn’t expect a physics lesson on this beautiful day. 2 The only physics needed, my friend, you learned as a child, so not to worry. The sketch is a top view, looking down on the earth’s north pole. You see the moon in its monthly orbit, moving in the same direction as the earth’s rotation. And while this is going on, the earth and moon together orbit the distant sun once a year, in about twelve months, right? Got it skippah.
    [Show full text]
  • Moons Phases and Tides
    Moon’s Phases and Tides Moon Phases Half of the Moon is always lit up by the sun. As the Moon orbits the Earth, we see different parts of the lighted area. From Earth, the lit portion we see of the moon waxes (grows) and wanes (shrinks). The revolution of the Moon around the Earth makes the Moon look as if it is changing shape in the sky The Moon passes through four major shapes during a cycle that repeats itself every 29.5 days. The phases always follow one another in the same order: New moon Waxing Crescent First quarter Waxing Gibbous Full moon Waning Gibbous Third (last) Quarter Waning Crescent • IF LIT FROM THE RIGHT, IT IS WAXING OR GROWING • IF DARKENING FROM THE RIGHT, IT IS WANING (SHRINKING) Tides • The Moon's gravitational pull on the Earth cause the seas and oceans to rise and fall in an endless cycle of low and high tides. • Much of the Earth's shoreline life depends on the tides. – Crabs, starfish, mussels, barnacles, etc. – Tides caused by the Moon • The Earth's tides are caused by the gravitational pull of the Moon. • The Earth bulges slightly both toward and away from the Moon. -As the Earth rotates daily, the bulges move across the Earth. • The moon pulls strongly on the water on the side of Earth closest to the moon, causing the water to bulge. • It also pulls less strongly on Earth and on the water on the far side of Earth, which results in tides. What causes tides? • Tides are the rise and fall of ocean water.
    [Show full text]
  • Tsunami, Seiches, and Tides Key Ideas Seiches
    Tsunami, Seiches, And Tides Key Ideas l The wavelengths of tsunami, seiches and tides are so great that they always behave as shallow-water waves. l Because wave speed is proportional to wavelength, these waves move rapidly through the water. l A seiche is a pendulum-like rocking of water in a basin. l Tsunami are caused by displacement of water by forces that cause earthquakes, by landslides, by eruptions or by asteroid impacts. l Tides are caused by the gravitational attraction of the sun and the moon, by inertia, and by basin resonance. 1 Seiches What are the characteristics of a seiche? Water rocking back and forth at a specific resonant frequency in a confined area is a seiche. Seiches are also called standing waves. The node is the position in a standing wave where water moves sideways, but does not rise or fall. 2 1 Seiches A seiche in Lake Geneva. The blue line represents the hypothetical whole wave of which the seiche is a part. 3 Tsunami and Seismic Sea Waves Tsunami are long-wavelength, shallow-water, progressive waves caused by the rapid displacement of ocean water. Tsunami generated by the vertical movement of earth along faults are seismic sea waves. What else can generate tsunami? llandslides licebergs falling from glaciers lvolcanic eruptions lother direct displacements of the water surface 4 2 Tsunami and Seismic Sea Waves A tsunami, which occurred in 1946, was generated by a rupture along a submerged fault. The tsunami traveled at speeds of 212 meters per second. 5 Tsunami Speed How can the speed of a tsunami be calculated? Remember, because tsunami have extremely long wavelengths, they always behave as shallow water waves.
    [Show full text]
  • Tsunamis in Alaska
    Tsunami What is a Tsunami? A tsunami is a series of traveling waves in water that are generated by violent vertical displacement of the water surface. Tsunamis travel up to 500 mph across deep water away from their generation zone. Over the deep ocean, there may be very little displacement of the water surface; but since the wave encompasses the depth of the water column, wave amplitude will increase dramatically as it encounters shallow coastal waters. In many cases, a El Niño tsunami wave appears like an endlessly onrushing tide which forces its way around through any obstacle. The image on the left illustrates how the amplitude of a tsunami wave increases as it moves from the deep ocean water to the shallow coast. Over deep water, the wave length is long, and the wave velocity is very fast. By the time the wave reaches the coast, wave length decreases quickly and wave speed slows dramatically. As this takes place, wave height builds up as it prepares to inundate the shore. Why do Tsunamis occur in Alaska? Subduction-zone mega-thrust earthquakes, the most powerful earthquakes in the world, can produce tsunamis through fault boundary rupture, deformation of an overlying plate, and landslides induced by the earthquake (IRIS, 2016). Megathrust earthquakes occur along subduction zones, such as those found along the ring of fire (see image to the right). The ring of fire extends northward along the coast of western North America, then arcs westward along the southern side of the Aleutians, before curving southwest along the coast of Asia.
    [Show full text]
  • Tidal Hydrodynamic Response to Sea Level Rise and Coastal Geomorphology in the Northern Gulf of Mexico
    University of Central Florida STARS Electronic Theses and Dissertations, 2004-2019 2015 Tidal hydrodynamic response to sea level rise and coastal geomorphology in the Northern Gulf of Mexico Davina Passeri University of Central Florida Part of the Civil Engineering Commons Find similar works at: https://stars.library.ucf.edu/etd University of Central Florida Libraries http://library.ucf.edu This Doctoral Dissertation (Open Access) is brought to you for free and open access by STARS. It has been accepted for inclusion in Electronic Theses and Dissertations, 2004-2019 by an authorized administrator of STARS. For more information, please contact [email protected]. STARS Citation Passeri, Davina, "Tidal hydrodynamic response to sea level rise and coastal geomorphology in the Northern Gulf of Mexico" (2015). Electronic Theses and Dissertations, 2004-2019. 1429. https://stars.library.ucf.edu/etd/1429 TIDAL HYDRODYNAMIC RESPONSE TO SEA LEVEL RISE AND COASTAL GEOMORPHOLOGY IN THE NORTHERN GULF OF MEXICO by DAVINA LISA PASSERI B.S. University of Notre Dame, 2010 A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Civil, Environmental, and Construction Engineering in the College of Engineering and Computer Science at the University of Central Florida Orlando, Florida Spring Term 2015 Major Professor: Scott C. Hagen © 2015 Davina Lisa Passeri ii ABSTRACT Sea level rise (SLR) has the potential to affect coastal environments in a multitude of ways, including submergence, increased flooding, and increased shoreline erosion. Low-lying coastal environments such as the Northern Gulf of Mexico (NGOM) are particularly vulnerable to the effects of SLR, which may have serious consequences for coastal communities as well as ecologically and economically significant estuaries.
    [Show full text]
  • How a Tide Clock Works.Pub
    Conventional time clocks have a 12 hour cycle, with 1 hand for hours, another for minutes. Tide clocks have a single hand, and a cycle of 12 hours 25 minutes, coinciding to an average time of about 6 hours 12 minutes between high and low tides. High tide is indicated when the hand is at the ‘12 o’clock’ position, low tide is indicated with the hand at the ‘6 o’clock’ position. A tide clock is not indicating 6 or 12 o’clock of course. It is merely a convenient reference point on the dial, showing us when our local tide is high or low. 12 is marked as High, 6 is marked as Low. However, the hour markings on the dial between the High and Low tide points do show us the number of hours since the last high or low tide, and the hours before the next high or low tide. A tide clock which has been initially set correctly will continue to display tide predictions quite accurately, requiring resetting only at intervals of about 4 months, depending upon the location. A brief explanation of how the tidal cycle works The Moon is the major cause of the tides. The ‘lunar day’ (the time it takes for the Moon to re-appear at the same place in the sky) is 24 hours and 50 minutes. New Zealand, and many other places in the world, have 2 high tides and 2 low tides each day. These are called semi-diurnal tides. Some areas of the world (eg Freemantle in Australia), have only one tide cycle per day, known as diurnal tides.
    [Show full text]
  • 2018 NOAA Science Report National Oceanic and Atmospheric Administration U.S
    2018 NOAA Science Report National Oceanic and Atmospheric Administration U.S. Department of Commerce NOAA Technical Memorandum NOAA Research Council-001 2018 NOAA Science Report Harry Cikanek, Ned Cyr, Ming Ji, Gary Matlock, Steve Thur NOAA Silver Spring, Maryland February 2019 NATIONAL OCEANIC AND NOAA Research Council noaa ATMOSPHERIC ADMINISTRATION 2018 NOAA Science Report Harry Cikanek, Ned Cyr, Ming Ji, Gary Matlock, Steve Thur NOAA Silver Spring, Maryland February 2019 UNITED STATES NATIONAL OCEANIC National Oceanic and DEPARTMENT OF AND ATMOSPHERIC Atmospheric Administration COMMERCE ADMINISTRATION Research Council Wilbur Ross RDML Tim Gallaudet, Ph.D., Craig N. McLean Secretary USN Ret., Acting NOAA NOAA Research Council Chair Administrator Francisco Werner, Ph.D. NOAA Research Council Vice Chair NOTICE This document was prepared as an account of work sponsored by an agency of the United States Government. The views and opinions of the authors expressed herein do not necessarily state or reflect those of the United States Government or any agency or Contractor thereof. Neither the United States Government, nor Contractor, nor any of their employees, make any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, product, or process disclosed, or represents that its use would not infringe privately owned rights. Mention of a commercial company or product does not constitute an endorsement by the National Oceanic and Atmospheric Administration.
    [Show full text]
  • A Near-Shore Linear Wave Model with the Mixed Finite Volume and Finite Difference Unstructured Mesh Method
    fluids Article A Near-Shore Linear Wave Model with the Mixed Finite Volume and Finite Difference Unstructured Mesh Method Yong G. Lai 1,* and Han Sang Kim 2 1 Technical Service Center, U.S. Bureau of Reclamation, Denver, CO 80225, USA 2 Bay-Delta Office, California Department of Water Resources, Sacramento, CA 95814, USA; [email protected] * Correspondence: [email protected]; Tel.: +1-303-445-2560 Received: 5 October 2020; Accepted: 1 November 2020; Published: 5 November 2020 Abstract: The near-shore and estuary environment is characterized by complex natural processes. A prominent feature is the wind-generated waves, which transfer energy and lead to various phenomena not observed where the hydrodynamics is dictated only by currents. Over the past several decades, numerical models have been developed to predict the wave and current state and their interactions. Most models, however, have relied on the two-model approach in which the wave model is developed independently of the current model and the two are coupled together through a separate steering module. In this study, a new wave model is developed and embedded in an existing two-dimensional (2D) depth-integrated current model, SRH-2D. The work leads to a new wave–current model based on the one-model approach. The physical processes of the new wave model are based on the latest third-generation formulation in which the spectral wave action balance equation is solved so that the spectrum shape is not pre-imposed and the non-linear effects are not parameterized. New contributions of the present study lie primarily in the numerical method adopted, which include: (a) a new operator-splitting method that allows an implicit solution of the wave action equation in the geographical space; (b) mixed finite volume and finite difference method; (c) unstructured polygonal mesh in the geographical space; and (d) a single mesh for both the wave and current models that paves the way for the use of the one-model approach.
    [Show full text]
  • II. Causes of Tides III. Tidal Variations IV. Lunar Day and Frequency of Tides V
    Tides I. What are Tides? II. Causes of Tides III. Tidal Variations IV. Lunar Day and Frequency of Tides V. Monitoring Tides Wikimedia FoxyOrange [CC BY-SA 3.0 Tides are not explicitly included in the NGSS PerFormance Expectations. From the NGSS Framework (M.S. Space Science): “There is a strong emphasis on a systems approach, using models oF the solar system to explain astronomical and other observations oF the cyclic patterns oF eclipses, tides, and seasons.” From the NGSS Crosscutting Concepts: Observed patterns in nature guide organization and classiFication and prompt questions about relationships and causes underlying them. For Elementary School: • Similarities and diFFerences in patterns can be used to sort, classiFy, communicate and analyze simple rates oF change For natural phenomena and designed products. • Patterns oF change can be used to make predictions • Patterns can be used as evidence to support an explanation. For Middle School: • Graphs, charts, and images can be used to identiFy patterns in data. • Patterns can be used to identiFy cause-and-eFFect relationships. The topic oF tides have an important connection to global change since spring tides and king tides are causing coastal Flooding as sea level has been rising. I. What are Tides? Tides are one oF the most reliable phenomena on Earth - they occur on a regular and predictable cycle. Along with death and taxes, tides are a certainty oF liFe. Tides are apparent changes in local sea level that are the result of long-period waves that move through the oceans. Photos oF low and high tide on the coast oF the Bay oF Fundy in Canada.
    [Show full text]
  • Atlantic Hurricane Activity During the Last Millennium
    www.nature.com/scientificreports OPEN Atlantic hurricane activity during the last millennium Michael J. Burn1 & Suzanne E. Palmer2 Received: 13 February 2015 Hurricanes are a persistent socio-economic hazard for countries situated in and around the Accepted: 10 July 2015 Main Development Region (MDR) of Atlantic tropical cyclones. Climate-model simulations have Published: 05 August 2015 attributed their interdecadal variability to changes in solar and volcanic activity, Saharan dust flux, anthropogenic greenhouse gas and aerosol emissions and heat transport within the global ocean conveyor belt. However, the attribution of hurricane activity to specific forcing factors is hampered by the short observational record of Atlantic storms. Here, we present the Extended Hurricane Activity (EHA) index, the first empirical reconstruction of Atlantic tropical cyclone activity for the last millennium, derived from a high-resolution lake sediment geochemical record from Jamaica. The EHA correlates significantly with decadal changes in tropical Atlantic sea surface temperatures (SSTs; r = 0.68; 1854–2008), the Accumulated Cyclone Energy index (ACE; r = 0.90; 1851–2010), and two annually-resolved coral-based SST reconstructions (1773–2008) from within the MDR. Our results corroborate evidence for the increasing trend of hurricane activity during the Industrial Era; however, we show that contemporary activity has not exceeded the range of natural climate variability exhibited during the last millennium. The extent to which the climate dynamics of the Main Development Region (MDR) of Atlantic tropical cyclone activity are controlled by natural or anthropogenic climatic forcing factors remains unclear1,2. This uncertainty has arisen because of the reliance on historical meteorological records, which are too short to capture the natural long-term variability of climatic phenomena as well as a lack of understand- ing of the physical link between tropical Atlantic SSTs and tropical cyclone variability3,4.
    [Show full text]
  • EARTH SCIENCE ACTIVITY #1 Tsunami in a Bottle
    EARTH SCIENCE ACTIVITY #1 Grades 3 and Up Tsunami in a Bottle This activity is one of several in a basic curriculum designed to increase student knowledge about earthquake science and preparedness. The activities can be done at any time in the weeks leading up to the ShakeOut drill. Each activity can be used in classrooms, museums, and other educational settings. They are not sequence-bound, but when used together they provide an overview of earthquake information for children and students of various ages. All activities can be found at www.shakeout.org/schools/resources/. Please review the content background (page 3) to gain a full understanding of the material conducted in this activity. OBJECTIVE: For students to learn that tsunamis can be caused by earthquakes and to understand the effects of tsunamis on the shoreline MATERIALS/RESOURCES NEEDED: 2-liter plastic soda bottles Small gravel (fish tank gravel) Water source Empty water bottle (16 oz) Overhead projector Transparency of Tsunami Facts “What Do I See?” handout PRIOR KNOWLEDGE: In order to conduct this activity, students need to know how fault slippage can generate earthquakes. ACTIVITY: Set-Up (Time varies) Collect as many 2-liter soda bottles as possible or ask students to bring in bottles for this activity (3 students can share one bottle). Obtain an empty water bottle (about 16 oz). Remove labels from all bottles. Purchase or gather enough small gravel to fit through the mouth of the soda bottles. Students will fill up their soda bottles with gravel to create at least a 2 inch layer on the bottom of the bottle.
    [Show full text]