Visitors on the Pismo Beach Pier can use binoculars to see plants and animals in the intertidal zone.

Minus Tides Return To Afternoons

Fall and Winter Best Seasons to See Spring Tides

Ó Bob Field 2000

They're Back! The daylight minus tides. Starting tomorrow for three days, October 26, 27, and 28, 2000 the Central Coast will have the first afternoon minus tides since early May. In the last six months, there has only been one minus tide after 10:30 am. While any low tide will do, minus tides are especially great times to visit a tide pool!

Locally the lowest tide of the year was -1.7 feet and the highest tide was 6.6 feet. Both occurred last January 20 during a full Moon. Every day we have two high tides and two low tides. The local mean lower low tide is defined as zero. Any tide lower than the mean lower low tide is a minus tide.

The next three minus tides are only a few inches below zero, but are still opportunities to study life in tide pools. The low tide turns at 4:33 tomorrow afternoon and you can go out an hour before it turns. The Moon rises nearly 50 minutes later each day as a result of the fact that it orbits the Earth once a month. Therefore the low tide occurs later each successive day.

When the Moon is full, it is on the opposite side of the Earth from the Sun. The gravitational pull of the Moon and the Sun work together to produce extreme high and low tides called Spring Tides (because they spring up, not because they occur in the spring). Locally the Spring Tidal range can be six or eight feet.

Spring Tides occur twice a month near a new or full Moon. They are best observed within a few months of the winter solstice when the Earth’s axis is tilted away from the Sun. The highest tide tends to occur around 9 am and the lowest tide occurs around 4 pm. The Spring Tides are also particularly strong near the summer solstice but occur inconveniently around 10 pm and 6 am.

When the Moon is in first or last quarter phases, the Sun and the Moon are pulling at right angles and the effect is not as great. This is called a Neap Tide. Locally the Neap Tidal range averages two to four feet.

Mankind has been fascinated by the daily, weekly, and seasonal variations in the tides for many millennia. The tides vary dramatically between different places. The patterns of the tides are complex because they are influenced by local, global, lunar, and solar factors. Tides have a great influence on our planet and on the abundance and diversity of life on Earth. And tide pools are wonderful places for explorers, young and old, to visit.

How can you learn more about the tides and tide pools? You can join one of the many docent-led walks to tide pools in Montana de Oro or other state parks. Since the tides are changing daily, check the newspaper, call the Natural History Museum in Morro Bay State Park to know the times and locations of these walks, or visit the Museum website at www.ccnha.org.

Visitors to the Museum can ask for free tide tables. The Museum is also displaying a temporary exhibit of photographs and diagrams of the tides and tide pools. Here you can learn why the tides aren't maximum when the Moon is directly overhead, why the Moon is more influential than the Sun, and why tides are so high in narrow bays like the Gulf of California and the Bay of Fundy.

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