Where is the best place to surf along the Washington coast
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Where is the best place to surf along the Washington coast What is a wave? How does a wave begin? Anatomy of a wave Label basic characteristics Define terminology What is a wave? A wave is a disturbance that propagates through space and time, usually with the transference of energy Ocean surface waves are perturbations that propagate through water How a wave begins – winds/storms The great majority of waves in the ocean result from winds Four factors that influence the formation of wind waves are: Wind speed Distance of open water that the wind has blown over, called fetch Time duration that wind has blown over a given area Water depth How a wave begins – geologic event Displacement of large volume of water caused by Earthquakes Volcanic eruptions Landslides Known as tsunamis (harbor wave) Usually generated when convergent plate boundaries abruptly move and vertically displace water How does an earthquake generate a tsunami? An earthquake may generate a tsunami if the quake: Occurs just below a body of water Is of moderate or high magnitude Displaces a large-enough volume of water Before earthquake Plate slips, plunges Energy released Overriding plate produces tsunami bulges under strain into water and releasing energy causing uplift Anatomy of a wave Fig. 10.3 Anatomy of a wave Waves are characterized by: Wave height (H) - measured from trough to crest Wavelength (L) - measured from crest to crest, or trough to trough Period (T) - time interval between arrival of consecutive crests or troughs at a stationary point Direction of wave propagation Waves (continued) I can determine the type of wave based on wavelength, depth, and speed. Wave motion Wave motion The speed of any surface wave (C) is equal to the length of the wave (L) divided by the period (T) Speed = length/wave period or C = L/T Longer L and T = faster waves Speed of a wave may change, but the period always stays the same Speed determined by L Fig. 10.5 There are 3 types of waves Deep-water waves D > L/2 Intermediate waves L/20 < D < L/2 Shallow-water waves D < L/20 Wave types Fig. 10.12 Wave steepness A breaking wave is one whose base can no longer support its top, causing it to collapse Steepness (S) = height/length or S = H/L If the ratio of height to length exceeds 1:7, the wave becomes too steep and breaks If L = 70 m, wave will break when wave height reaches 10 m Surf Zone The surf zone is the shallow area along the coast in which the waves rapidly, steepen, break and disappear in the turbulence and spray of expended energy Three main types of breaking waves identified by surfers Spilling, or rolling: these are the safest waves on which to surf. They can be found in most areas with relatively flat shorelines. They are the most common type of shorebreak Plunging, or dumping: these break suddenly and can "dump" swimmers—pushing them to the bottom with great force. These are the preferred waves for experienced surfers. Strong offshore winds and long wave periods can cause dumpers. They are often found where there is a sudden rise in the sea floor, such as a reef or sandbar Surging: these may never actually break as they approach the water's edge, as the water below them is very deep. They tend to form on steep shorelines. These waves can knock swimmers over and drag them back into deeper water Where is the best place to surf along the WA coast? La Push Westport Check the surf forecast before you go http://www.stormsurf.com/page2/links/orsrprt.shtml Why do you see tsunami evacuation route signs along HWY 101? Tsunamis are waves with long wavelength (100-200 km) and long periods (10-20 minutes) Average ocean depth is 4 km Tsunamis are shallow-water waves Propagate at speed determined by ocean depth at site of disturbance Energy of tsunami is distributed from ocean surface to ocean floor over the length of the wave When wave path is blocked by coast or island, the wave acts like shallow-water wave Slows Wavelength decreases Energy is compressed into smaller water volume as depth rapidly decreases Wave height rapidly increases If you’re at sea, head toward the source of the earthquake. If you’re near the coast, run uphill. Why do you see tsunami evacuation route signs along HWY 101? Earthquakes with a magnitude of 8 or higher occur in our area every 500 years on average Last known quake with a magnitude of 9 occurred at 9pm on January 26, 1700 Based on Japanese records of tsunami Clue linking tsunami in Japan and Cascadia subduction zone earthquake comes from study of tree rings showing last year of growth in red cedars was 1699 Native stories of large wave in PS and along coast Deposits Unearthing Proof of a Tsunami in the Northwest http://www.npr.org/templates/story/story.p hp?storyId=4629401 1964 Alaskan earthquake and tsunami Ghost Forests Tree drowning 1. Living coastal forest 2. Land level drops, tidewater drowns tree roots 3. Tidal mud accumulates and salt marsh develops Soil Deposits Earthquakes cause tsunamis 1. The coast before an earthquake 2. Land level changes during an earthquake, tsunami waves generated 3. Tsunami surges onto shore 4. Sand deposited over the land Tsunamis in the Pacific 1700 Cascadia tsunami model Tsunamis is the Pacific Alaskan earthquake of 1964 was the largest earthquake in North America and the second largest ever recorded Epicenter in N. Prince William Sound 8.4 to 8.6 75 miles E of Anchorage 4-5 minutes Killed 9 people Tsunami generated by tectonic uplift of seafloor and submarine landslides Killed 106 people
