1. Tides

2. What are they? The rhythmic rising and falling of ocean surface levels.

3. Why study them? Affect the coastline Affect the life of marine organisms in tidal areas Raise and lower sea level Affect lives of people Drive circulation in bays and estuaries

4. What causes tides? 1.Gravitational pull of the sun and moon on the Earth

5. 1. Gravitational Pull Moon pulls water on earth’s surface wherever it faces earth causing a bulge.

6. Result looks something like this:

7. most places on earth have 2 high tides and 2 low tides each day.

8. But there’s more… One rotation of earth takes…

9. But there’s more… One rotation of earth takes…24 hours The moon advances a little on its own rotation each day & it takes a spot on earth 50 minutes to “catch up” So one tidal cycle high – low – high again takes 24 hours and 50 minutes Tide charts predict when high and low tides will occur

10. How does the sun affect tides? Also has a gravitational pull on earth But the sun is 400 times farther away so the pull is not really noticed Except…

11. Spring Tides – straight line New Moon Earth Pull from moon combined with pull from sun. Result: exceptionally (wicked) high HIGH TIDES and exceptionally (wicked) low LOW TIDES

12. Spring Tides Full Moon Earth Pull from moon on one side and pull from sun on opposite. Result: exceptionally high HIGH TIDES and exceptionally low LOW TIDES

13. Neap Tides – Earth, moon and sun at a right angle Earth First quarter Third quarter Small difference between high and low not significantly great because sun and moon’s gravitational pull “cancel” each other out

14. Types of Tides Semidiurnal – two high, two low each day (most common) Mixed semidiurnal – successive high tides of different heights (most of U.S. west coast) Diurnal – One high and one low each day. (very uncommon)