Waves , Tides, Currents

1. Waves, Tides, Currents Chapter 20

2. Waves • Caused by wind (stronger = bigger) • Swells in ocean turn into waves on beach • Breaker is when wave crashes • Whitecaps are on the ocean (water + air) • Rogue waves are 2 or more combined, tall • Tidal bore are when waves travel upriver

3. Tsunami • Caused by earthquake, landslide, or volcano in ocean • Usually 3 or more waves between 15 and 60 minutes apart (can last all day) • Set up seismic recorders in ocean to warn and evacuate people on land in time

4. Tides • Rise and fall of shoreline (range is difference) • Time between high and low tide is about 6 ¼ hours • Can find tide schedule online or in daily newspaper (or an app) • Animals use tides to reproduce

5. Cause • Moon pulling on earth (gravity) • Spring Tide- new and full moon, tide is highest • Neap Tide- quarter moons, tide is lowest • Perigree- moon rotation close to earth, high • Apogee- moon rotation far from earth, low • Perihelion- close to sun (January), high • Aphelion- far from sun (July), low

7. Currents • Global ocean are largest • Continuous moving water (like rivers in ocean) • Cause: spinning of Earth • Wind and surface waters move clockwise in north, counterclockwise in south • Continents cause gyres (circles)

9. Types • Vertical- temp. and salinity causes current to move under another • Deep Ocean- countercurrents flow opposite of surface , creates upwelling (mix nutrients) • Waves create a sandbar (like a dam), riptide can break and cause undertow (returning current) • Tidal current runs parallel to shore and whirlpool is when surface creates circle

10. Effects • Cause erosion, can destroy homes nearby • Solutions? (consequences for all): • Groin (wood or rock)- straight out from sand • Jetty- traps sand preventing accumulation in channel • Breakwaters (rock) offshore • Dredging- sand from seafloor dumped on beach • Seawalls- prevent flooding

11. Plum Island, MA