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16_coast_09_post - 16 Surface Processes 3 Tides Waves and...

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Tides & Waves: 1 16: Surface Processes 3 Tides, Waves, and Coastlines Rocky shoreline, Oregon. Photo: Steve Terrill Barrier islands Photo: NASA Tides & Waves: 2 Why this is important Most waves are caused by wind, which is driven by Earth’s external heat engine. Surfers off Maui coast. Photo: R.W. Schlische Tides & Waves: 3 Why this is important 60% of global population live on or near coast. Coastlines are dynamic features that represent a huge investment in property, recreation, etc. Photo: W.K. Hamblin Photo: W.K. Hamblin Tides & Waves: 4 Fig. 18.15 Tides Size of intertidal zone depends on… Tidal range Side view Block diagram
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Tides & Waves: 5 Tides Q1. Approximately how many high tides occur per day? A. 1 B. 2 C. 3 D. 4 Q2. Approximately what is the difference in time between two successive high tides? Q3. Is the time of high tide the same for each day of the month? A. Yes B. No Q4. Is the height of high tide the same for each day of the month? A. Yes B. No Time/height of low tide Time/height of high tide Time/height of low tide Time/height of high tide Hours Tide height Tides & Waves: 6 Fig. 18.15 Tides : rise / fall of sea surface caused by gravitational pull of moon and sun and centrifugal force caused by the revolution of the Earth-moon system around its center of mass. Approx. 2 high tides per day due to Earth’s rotation beneath tidal bulges Tides Tides & Waves: 7 Tides: Analogy Top views Tides & Waves: 8 Tide-generating forces Each point on Earth feels same centrifugal force due to spin of Earth-moon system around its center of mass but feels different gravitational attraction due to pull of moon (e.g., force is greatest closest to moon). Tide-generating force is sum of centrifugal force and gravitational attraction. On side of Earth closest to moon, tide-generating force vector is dominated by gravitational force and points toward moon. On opposite side, centrifugal force dominates, and tide- generating force points away from moon. Thus, two tidal bulges exist. Side views
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Tides & Waves: 9 Tides Low tide Bay of Fundy, Nova Scotia, Canada Tidal amplitude varies greatly around the world (~1-2 m in NJ, up to 16 m in Bay of Fundy). Amplitude depends on latitude and shape of coastlines. For example, the Bay of Fundy acts like a funnel that forces water higher and higher near its narrow end during high tide. High tide Map views Tides & Waves: 10 Fig. 18.15 Tides Top view Top view Spring tides : tides with higher- than- normal tidal range that are produced when the Earth, Moon, and sun are aligned. Neap tides : tides with lower-than- normal tidal range that are produced when the moon is at right-angles to the Earth-sun system. Tides & Waves: 11 Review Questions 16-1. A. True / B. False: Coastal processes are of interest to geologists, but affect relatively few people because less than 10% of the world’s population lives within 10 km of a sea coast.
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