Chapter 3 Flashcards
What are tides?
Tides are the steady rise and fall in water level resulting from the gravitational pull of the moon and sun on large bodies of water.
How do tides affect divers?
- Tides can make the water at a particular dive site noticeably deeper or shallower than may have been expected.
- Tidal currents can be very strong making diving difficult or even dangerous.
- Strong tidal currents can have an adverse effect on visibility.
When should you enter and exit water?
During slack tide
What is slack tide?
The period between high and low tides, when there is the least amount of current.
What affects offshore currents?
Offshore currents are affected by the sun warming the water near the equator, coupled with the rotation of the Earth. They move warmer water toward the poles and cooler water toward the equator.
What is a longshore current?
A longshore current runs parallel to the shoreline.
What causes longshore currents?
They are generally caused by waves approaching the shore at an angle, but factors such as tide and the presence of permanent offshore currents may have an impact.
How do you want to plan a dive when there are longshore currents?
You want to plan your entry well-up current from your exit point.
What is a rip current?
A rip current is a narrow flow of swiftly moving water that runs perpendicular to shore.
How are rip currents formed?
They are formed when water flowing out to the sea is funneled through a narrow restriction.
How can you identify a rip current?
You can identify a rip current by a stream of foamy turbid water running perpendicular to shore.
What causes waves?
Waves are caused by wind pushing water on the surface.
What is fetch?
How hard and long the wind has been blowing and the distance the wind has travelled without being obstructed.
What is wavelength?
The distance from the crest of one wave to the crest of the next wave.
What is surf?
Breaking waves at a shoreline.
