Ocean 10 Lab #8

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Mt San Antonio College *

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10

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Geography

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Dec 6, 2023

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11

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I~ . s ——e Ocean Waves and Tides Lab The content of this lab exercise was modified from content provided by Professors Lackey and Anders at Mt. SAC, in addition to Teachers Pay Teachers. Overview Ocean waves are pulses of energy that move across the surface of the ocean (surface waves) or at depth (internal waves). Surface waves are caused by wind, glacial melt, underwater landslides, asteroid impact, offshore earthquakes (these waves are called tsunami), or are generated due to the Moon’s gravity (these waves are called tides). Internal waves are caused by differences in deep water current flow, usually due to temperature, density and salinity conditions (these are plotted as graphs, and the boundaries are referred to as thermoclines, haloclines and pycnoclines). All waveforms have the same physical characteristics. These include the crest—the highest point of the waveform, the trough—the lowest point of the waveform, the wavelength—the distance between two crests/troughs, the wave height, or amplitude—the difference between the height of the crest and trough, and the period—the amount of time taken for two successive waves to pass a fixed point. Wind generated waves have a different period, height and wavelength as compared with tsunami or tide generated waves, as we will investigate in the exercises on the next few pages. Water waves move not only progressively—creating a series of crests and troughs that move laterally with energy dispersal—but also generate a continuous circular flow, termed orbital motion. The combined effect of orbital motion and the forward motion of waves ultimately causes floating objects to advance in the direction of wave travel. The wave base is the depth where the orbital motion stops; it is equal to % wavelength (Figure 1). Avade wond 5—5(,(\(\‘13 9 A\ Avbanc e : —— direction of wave travel C)prpfirre,s.‘vc lj Swi¥+ o <+—— wavelength (L or A) from crest-to-crest ————» 5 4 3 2 1 height or amplitude \ wave orbital = N motion J fre sé's“'c trough average still water level O O X O O O trough passes overhead crest passes Figure 1. Ocean waves and their physical characteristics: crest, trough, height, length and orbital motion.
‘—W 2 R A St L Wave Anatomy and Behavior E T(oqé;/' \ Cs F Open ocean - Approaching shore SR - .l. Surf I ,- waves with constant waves touch bottom {breakers form) y - Figure 2. A 3D cross section of ocean waves traveling from left to right. Essential wave parts are marked as A through F (modified from Tarbuck, Lutgens, Pinzke, 1997, Applications and Investigations in Earth Science, p. 157). Figure 2 above shows that wavelength of open ocean waves remains constant as long as wave base does not make contact with the sea bottom. Such waves are called deep-water waves. Deep-water waves eventually become shallow-water waves as they travel toward continents and encounter shallowing water over the continental shelf. Once wave base "feels" the sea bottom, an open-ocean, deep-water wave transforms into a shallow-water wave. Ultimately, ocean waves arrive at the shallowest depths of the ocean at beaches. Here, they build-up in height, become unstable, and collapse forward, breaking. Orbital motion is then converted to forward motion as water rushes up the beach face (also known as swash zone and foreshore) then back down the beach face as backwash. Overview and Wave Behavior Questions 1. Match the lettered parts of ocean waves (A through F) in Figure 2 above with the names below. e Wave Crest: Wave Length: Orbital Motion: + Wave Trough: Wave Height: D Wave Base: 2. Figure 2 illustrates that after wave base makes contact with the sea bottom, wave velocity decreases. Wave height and wavelength are affected as well. What change in wave height and wavelength can you observe in Figure 2?' e Change in wave height: \wo\ve. hfi‘\%\(\\ increases B * Change in wavelength: {, ave_ '\.Qy\?j\/\ C\C(,f coseS . - Ve M‘;a;ffé WMAKES CONTOCT Lot oot rom /. ‘:’e"{D iy A
F TS LY e S.hml,t-“wflghtlne(hammmVu»fi@;)annectsaflrhe centers of the wave orbitals for all the waves pictured. DY aLpV\ 4. To further help you understand why ocean waves break, examine the breaking wave farthest to the right. How is the position of the bottom-most orbital different from the position of orbitals above it? QRN vodionS 1S detre®ing Aownwards ¥rom the Sor Face. Wt W of Ane Sulfoce ywortteR 1S highy Compaved QY e deptn. Wen gt fncceaseS ix \oreates, Wave Height Most ocean waves are created by the wind. Three factors control the height of deep- water waves: 1) Wind speed - the faster the wind blows the higher the waves become 2) Wind duration the longer the wind blows across the ocean surface, the higher the waves become 3) Wind fetch (fetch is the surface distance of the ocean across which the wind blows) the greater the fetch the higher the waves become There is a maximum height that waves will reach, such that above a certain wind speed, duration, and fetch, more waves will be created but the increase in wave height stops. Figure 3 plots wave height against fetch. The curve represents the amount of time, in hours, that wave height lasts (e.g., 15 h=15 hours). wn » W N Wave height, H, In meters - 00 200 400 600 800 1000 Fetch, F, in kilometers Figure 3. Graph of wave height (y-axis) vs. wind fetch (x-axis) showing the change in wave height for changes in wind duration in increments of 5 hours. This graph is from Thurman and Savin, 1995, Laboratory Exercises in Oceanography, p. 91.
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2 " ¢ e . 1. Use the above graph (Figure 3) to estimate wave height for the following wind durations: a. 5hours (5" 2.7 mexersS b. 30 hours (30") S 2 medersS Shore Processes and Modification of Coasts
Modification of Coasts Questions 1. Compare the photo below with F photograph of Point Lookout on Long Island The sandy beach has been stabilized tempoi "groins” that extend seaward and rol Laboratory Exercises in Oceanography, p. lfi. reakwater and deposit sand inside the of Oceanography, pp. 319-320). igure 4a on the previous page. The photo is an aerial , New York. North is toward the top of the image. rarily with 3 hard engineering structures called ughly perpendicular to the shore (from Pipkin et al, 2001, E w Lovashoce o€ c\,Y:‘fiu - ] Cucrent— Seat A o o Flow of wove ot parmllels Mox o ok (s e corrent, parallel 4o Ane beach face S et Yo east a) Inthe photo, what is the direction of longshore current relative to north? &G b) From the photo, what is the visible evidence that indicates the direction of the longshore _ (r\y current and therefore the direction of sand transport? 0:-SYem °°'a coX the avoin \0\‘7 < ¢) Assuming that North is toward the top of the photo, label the side of the westernmost "V\\r:' e N groin with the letter, D, for the side of the groin where sand has been deposited, and the et letter, E, for the side of the groin where sand has been eroded. D(W(\
2 Whmhm@fiomermequesmbebw 2. Give the geographic direction, relative to North, for the flow direction of the longshore current (indicated as “littoral drift” in the figure). Lov‘fi%\no(b QO \ S MoVIng codt 3. Record the following in Figure 5: 1) the direction of littoral drift (i.e. the direction that sand was transported in the longshore current), 2) the direction of wave approach, 3) the location of the breakwater, which is a “hard” coastal engineering structure, built of large chunks of quarried rock called rip-rap and put in place by coastal engineers to protect boats moored on the leeward side (i.e. the side facing the beach or the side opposite to that facing incoming waves), 4) the seaward build-out of sand at Location B, 5) the location of the pier. Figure 5. Sketch of the breakwater and resultlng effects at the beach at Santa Momca CA pnor . to 1970 (from Pipkin and others, 2001, Laboratory Exercises in Oceanography, p. 135). 4. Of the 3 locations, A, B, and C, which will receive the full impact of incoming waves? = \C\ 5. What effect does the breakwater have on wave energy at Location B? Sediment < depoSried-thele 6. What effect does the pier have on the flow of the longshore current? TY SYopS \orgdnore A ik 7. Offer a simple explanation as to why sand has built-up seaward at location B. Include the following in your explanation: 1) the effect of the breakwater and the pier, and 2) the ability of the longshore current to erode sand compared to the rate of sand build-up from incoming waves obstructed and slowed by the breakwater. ’Y\r\e e VoS lolocte e Ylouww OFae \ww% COUSY Sedimentd Yo Ceposit 7. 'W\e \QF@QKW&*C‘% Aot S e Sawmc oS e (»fo
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Tides For this part of the lab, you will analyze tide data collected by the National Oceanic and Atmospheric Administration (NOAA) for January 2011 in New York. You will be comparing the predicted highest high tides and lowest low tides in a month to the phases the moon is in at the same time. The NOAA has about 3000 stations that collect tide data from all over the country. The values you will be analyzing were predicted for a station at the end of Manhattan in New York Cityina place called The Battery. To the right is a map of where the station is as well as a picture of the station itself (inside the shed are the scientific instruments measuring data all the time). Pre-Lab Questions: Read about the tides on the Geology Café website, then answer the questions below: 1. How many high tides occur most days? Two h‘\%\h FideS 2. How many low tides occur most days? oo \ow YdeS e (e O Suit st Aee afin A Cavity Hypothesis: Predict what phase(s) the moon will be in when tides are furthest from the average (higher and lower). be Ve e woon i\ \oe o\ vwoen, Tides Lab Questions 1. Use the Tide Predictions for January 2011 data table to plot the low tide data on the prepared graph. Connect each data point with a line. Most days will have two data points. . Label the line “Low Tide”. . Use the Tide Predictions for January 2011 data table to plot the high tide data on the prepared graph. Connect each data point with a line. Most days will have two data points. Use a different color than used in step 1 if possible. . Label the line “High Tide”".
OCEA10L-Mt SAC-Professor Diana L. Pomeroy-Fall 2020 5. Find, circle and label the following locations on your graph: highest low tide, lowest low tide, highest high tide, lowest high tide. o Use the Moon Phases for January 2011 data to find the date for each phase on the plotted graph. Circle each date and label the phase that occurs next to that date on plotted graph. ~ . Use your graph to complete the following questions: o On what date was the lowest low tide? \-72-20 \| What was the tide height? -4 e On what date was the highest low tide? !-2-22\ what was the tide height? 4 & foe On what date was the lowest high tide? 1~ 20\l What was the tide height? 3A o a e On what date was the highest high tide? \-20-20!{ What was the tide height? s [¢] . When the high tides were at their highest for the month, were the low tides also at their highest? If not, where were they at? Explain. '\\’\4—‘6 A& noY Seet Ao Cooce\nde f. Is there any relationship between the lowest high tides of the month and t&\i\highest low tides? Explain. 86 pc 0F NdeS opfn Hcooahovt Hne eginging ang w (\,\'cof"\\f\c,wwnr\“f‘:. J 9 o On your graph you can notice there are two times during the month when the high tides were higher than normal and the low tides were lower than normal. What two phases of the moon occurred around these times? Phase #1: £\)\\ wwON Phase #2: ‘\(:\)\\ Moo h. On your graph you can also notice there are two times during the month when the high tides were lower than normal and the low tides were higher than normal. What two phases of the moon occurred around these times? Figsr quorice do the Phase #2: Newd WO +0 e Yull moov £ivs GL()MH‘QK Phase #1: Conclusions: 1. How did your hypothesis stand up? Does the phase of the moon have an effect on the height of the tides? Explain. )"“3 \\\bPO*\\\eSiS Seem S Jo be C'O(ch‘l- | lpecavse the high anés low 4ide$ correladte With Ahe Joil and hew moont Flf\o\S&S_
OCEA10L-Mt SAC-Professor Diana L. Pomeroy-Fall 2020 2. Aspring tide (when high tides are higher and low tides are lower than average) occurs around the time of the new moon and full moon. Neap tides (when high tides are lower and low tides are higher than average) occur around the time of the first and third quarters. The diagram below shows when the spring and neap tides occur. Using the tide data from January 2011 included in this experiment, label the diagram below with the dates of the spring and neap tides that occurred. Date: \’2’20\ \ Spring tide Newgoo" /< \r%eaptide pate: \ 24 -\ | First quarter rnoonO a O‘lhird quarter moon O Spring tide Date: \ 22—\ 3. Which tides are higher than normal during a spring tide, low or high tides? Based on the diagram above explain why you think this happens. (Hint: it has to do with gravity) The MonS et on oomv‘»*g COLSTS }\'\ob\(\ xides o be \0'\%0( Aoving Fre et Zuo\(m,
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OCEA10L-Mt SAC-Professor Diana L. Pomeroy-Fall 2020 Tide Predictions for January 2011 New York City date | low tide (feet)*| high tide (feet)* date |low tide (feet)*| high tide (feet)* 1/1/2011 -0.3 5.1 |1/16/2011 0.1 3.7 1/1/2011 a1| |1/17/2011 -0.1 4.7 1/2/2011 -0.3 s.2| |1/17/2011] 4 1/2/2011 -0.5 42| |1/18/2011 -0.2 5.1 1/3/2011 -0.3 s.2| |1/18/2011 -0.5 4.3 1/3/2011 -0.5| 43| |1/19/2011 -0.5 5.3 1/4/2011 -0.3 5.2| |1/19/2011 -0.8 4.5 1/4/2011 -0.6 43| |1/20/2011 -0.7 5.5 1/5/2011 -0.3 5.1 [1/20/2011 -1 4.8 1/5/2011 -0.6 43| |1/21/2011 -0.9 5.5 1/6/2011 -0.2 49 |1/21/2011 -1.1 4.9 1/6/2011 -0.4 42| |1/22/2011 -0.9] 5.3 1/7/2011 0| 47| |1/22/2011 -1.1 5 1/7/2011 -0.3 41| |1/23/2011 -0.7 5.1 1/8/2011 0.2 45| |1/23/2011 -0.9| 5 1/8/2011 -0.1 4| |1/24/2011 -0.5 4.8 1/9/2011 0.5 42| |1/24/2011 -0.6 1/9/2011 0.2 1/25/2011 -0.2 4.9 1/10/2011 0.7 4| |1/25/2011 -0.3 4.5 1/10/2011 0.4 3.9 |1/26/2011 0.1 4.9| 1/11/2011 0.9 39| [1/26/2011 -0.1 4.2 1/11/2011 0.6 37| |1/27/2011 0.1 4.7 1/12/2011 1 3.9 |1/27/2011 0] 3.9 1/12/2011 0.7 35| [1/28/2011 0.1 4.7 1/13/2011 0.9 3.9 |1/28/2011 0.1 3.8 1/13/2011 0.7 3.4 |1/29/2011 0| 4.6 1/14/2011 0.7 4| |1/29/2011 0 3.8 1/14/2011] . 05 3.4] |1/30/2011 -0.1 4.7 1/15/2011] - 0.5 42| |1/30/2011 -0.1 4 1/15/2011 0.3 3.5 |1/31/2011 -0.3 4.8 1/16/2011 0.2 44| |1/31/2011 4.1 *Height is measured from an average Moon Phases for January 2011 New Moon Jan.4 First quarter Jan. 12 Full Moon Jan. 19 Third Quarter Jan. 26 10
OCEA10L-Mt SAC-Professor Diana L. Pomeroy-Fall 2020 January 2011 Tides TT0Z/TE/T ~ |-1T02/0€/T - -T102/62/1T - |-ttoz/82/T —1102/LT/T —1102/92/T —1102/52/1 —1102/v2/T —-T10Z/€T/1T —1102/22/1 ~fTT0T/12/T - t10Z/0Z/T —1T0Z/61/1 —1T0Z/81/1 - b-t10Z/LT/T —1102/9T/1 —110Z/ST/T —1T0Z/¥1/T —TT0Z/€T/T -110Z/2T/1 —TT02/11/T - |-tt0z/01/T - +1102/6/1 - -1102/8/1 =T1102/L/T - -F1102/9/1 - =T1102/8/1 - 110Z/t/1 —~TTOZ/€/T —1102/2/T L L L L < o~ 0w WY < N W W = N B I . IS IS IR I N B 46 18 (3934) 3y319H 110Z/1/1 Date 11