shores and coastal processes!one of the most dynamic and popular environments on Earth…!shore: strip of coast closest to sea/lake, may have a beach!> 50% of US population lives < 80 kms from ocean or Great Lake!coast: entire region bordering body of water!shoreline: precise boundary of water and dry land!consequence of living near the coast: coastal erosion!prediction of future shorelines!to 2050 in Long Beach, CA!what is responsible for coastal erosion?!we have examined numerous processes!of erosion, transportation and deposition!• mass wasting!• streams!• ground water!• glaciers!• wind!waves!ordinary ocean waves are produced by wind!wave hitting coastline transfers wind energy to coast! …eroding rocks and transporting sediments…!storms increase wave energy and increase erosion!wave period: time for one wavelength to pass!– ocean wave velocities range from 25 to 90 km/hr!water waves!wave height: vertical distance between crest and trough!– crest: highest point on wave "trough: Lowest point on wave!– ocean waves range from 0.3 to 5 m high; can be much higher!wavelength: horizontal distance between 2 crests or troughs!– ocean waves range from 40 to 400 m!southern ocean has unlimited fetch: no land masses!wave height, length, period and velocity are controlled by!• speed and duration of wind!• constancy of wind direction!• distance wind travels across water surface (fetch)!routinely has waves exceeding 15 m (50 feet)!…largest wind-generated wave ever observed was in 1933 by captain !of USS Ramapo in northern Pacific---34 meters high (115 feet)---!rogue wave !off!South Africa!from Esso!supertanker!-- 10 m high --!waves from different winds may interfere!constructive interference: !"sum together to generate bigger wave!destructive interference: !"cancel to produce smaller wave!blue + red interfere to produce green!big waves in Malibu may start from Antarctic storms and !grow from interference from Hawaiian rain squalls!water waves!motion of water in waves is nearly circular--orbit!energy advances with the wave but water does not!orbital motion decreases with depth and is gone at!depth of 1/2 the wavelength!wave base: depth where orbital motion is zero!• in deep water, waves have no effect on sea floor!water waves!where water depth < 1/2 wavelength, waves “feel” bottom!• bottom of wave slows down (friction from sea bottom)!• top of wave moves faster, water piles up and topples over !"(“breaks” in surf zone)!• in shallow water, waves may disturb sediments on sea floor!water waves!energy moves water from wave up beach as “swash” !"and deposits sediments!gravity moves water down beach as “back swash” and !"removes sediments!water waves in the nearshore!what happens when waves approach shore at an angle?!refraction--waves bend and change direction!• waves slow down in shallow water!• waves move closer together!• waves in deeper water!travel faster and !“catch up” to wave!in shallower water!• effect is for waves!to bend as they approach!the shore to be close to!parallel to the shore!(the waves still are at!a small angle to shore)!wave refraction!wind and wave direction!component perpendicular!"to beach!component parallel!"to beach!waves approach shore at an angle!beach!beach parallel component produces longshore current!swash moves!sediment up beach!at an angle!back swash moves!sediment straight!down beach in !response to !gravity!net effect is to!move sediment!parallel to beach!in direction of!longshore current!longshore drift: movement of sand parallel to shore!sand grains move suspended in surf zone!longshore drift: leads to depositional land forms!spit: ridge of sand that extends from land into!open water!longshore current meets!deep, quiet water of bay!and drops sediment load!-- forms spit --!longshore drift: leads to depositional land forms!baymouth bar: ridges of sand, transported by longshore currents, that cut off bays from the open ocean -- starts as spit that grows across opening!bay mouth bar!longshore drift: leads to depositional land forms!tombolo: bar of sediment connecting a former island (typically composed of bedrock) to the shore (deposition behind sea stack as refracted waves slow down)!tombolo!water waves in the nearshore!rip currents: -- fed by water in surf zone !" " -- form from wave interference!• flow straight out to sea from surf zone!• travel at the surface and die out at depth!• carry fine grained particles (and surfers) to deeper water!• form narrow currents perpendicular to shore, allowing swimmers!"to swim parallel to shore to escape them!• interfere with incoming waves!…twice daily rise and fall of ocean surfaces!gravitational pull of Moon and Sun and rotation of Earth! Sun is bigger but farther away--exerts only 40% of pull of Moon!high tide: face of Earth toward Moon! • strong gravitational pull of Moon!high tide: face of Earth away from Moon! • weak gravitational pull of Moon! • spinning force from Earth rotation is at!"maximum and causes bulge of water!2 high tides per day at every location (Earth rotates)!2 low tides at points midway between high tides!tides!flood tide: rising, elevates water, advances shore landward!ebb tide: falling, lowers water surface, shore recedes!tidal bore: flood tide whose upstream motion is turbulent!" "Bay of Fundy: tidal bore is 10-15 km/hr!amount of change in water level depends on coastline shape!and size of body of water!• narrow inlet forces water to pile into small area--Puget Sound: 3-4 m!• straight coastline has little effect--open Pacific at Hawaii: 0.5-1.5 m!Bay of Fundy!turbulent!beach!strip of sediment from low-water line inland to a cliff or !" " ""zone of permanent vegetation!beach face: !steepest part of beach, !water sloshes up as !waves are breaking!berm: !flat or gently sloping!platform!--narrowed during storms!--rebuilt during calms!marine terrace: !broad, gently sloping platform or rock or sediment just offshore!beach features, CA!backshore!foreshore!berm!beach: seasonal development!winter: frequent storms; high wave energy!"…sand eroded from beach anddeposited as “bar” offshore!summer: rare storms; low wave energy!"…sand eroded from bar and redeposited on beach!beach: depositional feature (sources of sand)!• deposition from rivers (> 90%)!• erosion of local cliffs!• transport from regions seaward of surf zone!• bioclastic (shells of organisms--carbonates)!• longshore