Tides are periodic rises and falls of large bodies of water caused by the gravitational interaction between the Earth and the moon.
The gravitational attraction of the moon causes the oceans to be pulled in the direction of the moon. Another pull occurs on the opposite side, as the Earth is pulled toward the moon (and away from the water on the far side). Since the Earth is rotating while this is happening, tides occur twice a day, about 12 hours and 25 minutes apart. As the moon orbits the Earth, this pull does not occur in the same place at the same time each day, meaning the times for high and low tides change by about 50 minutes daily.
During the full moon and the new (not visible) moon, the Earth, Sun and moon are alligned, causing higher high tides and lower low tides. This effect is called a Spring tide. During the first and last quarter Moon, the Sun and Moon pull in opposite directions and the high tides are a little lower and the low tides a litter higher. This is called a Neap tide.
Tidal flats (which are exposed at low tide), along with intertidal salt marshes and mangrove forests, are important ecosystems. They usually support a large population of wildlife, and are often of vital importance to migratory birds, as well as certain species of crabs, mollusks and fish.
Tidal flats have three basic environments:
Supratidal
Intertidal
Subtidal
The supratidal zone is above high tide and sediment deposits are exposed to subaerial conditions most of the time with flooding only during spring, king or storm tides. This zone is divided into vegetated and non-vegetated intertidal mud flats and sand bodies.
The intertidal zone lies between normal low and high tides and is exposed once or twice daily. Periods of submergence favours deposition of silts, clays and muds in the high tidal flats, interbedded mixed lithologies of mud and sand in the mid-flat zone, and linear shoals or bars of sand deposited by tidal currents in the low tidal flat zone.
The subtidal zone is below low tide and seldom exposed. It is a belt of muddy sediment and grassy marsh that is predominantly pelletized and burrowed.
To claim this Earthcache:
1. Go as close as you can to the waypoint (1.2km from the beach or beyond during a Spring tide) without getting your feet wet and post a photo of yourself or your GPSr if you wish (photo optional).
2. Include your GPS location, time, date and distance to the waypoint when you log the find. State what zone (or part of a zone) you are in. What features were seen at your waypoint that confirm the type of zone?
3. Mention if your visit was at low, high or in-between tides and what direction was the tide, flood or ebb?
You may log your visit immediately when you add your responses to the questions above in your post.
Bonus points if you visit on a Perigean Spring Tide (King Tide) which is a tide that occurs three or four times a year when the Moon's perigee (its closest point to Earth during its 28-day elliptical orbit) coincides with a spring tide. This tide usually adds a few centimetres to normal spring tides.
Townsville tide information can be found here.
Why not check out my two other tidal caches while you're nearby GC7NTCQ Shipwrecked Again and GC6GQ5R Tidal Choice
Congratulations to Karicka for being the FTF.
