Pary Heistuman, age 11, of Eugene, Oregon, for her question:

Why are the Hawaiian tides hardly noticeable?

The tides are great individualists. Almost everywhere they repeat their schedules every 24 hours and 50 minutes    with slight variations. But the details are different along every shore. Where the Pacific meets the shores of Oregon, the rising water surges high and ebbs down low. We might expect the same ocean to wash the island beaches of Hawaii with similar strong highs and lows. But there the rise~and fall of the gentle tides is hardly noticeable.

Young Isaac Newton figured out the tides obey a global rhythm, as the earth rotates its surface under the moon. But sailors learned that this neat global pattern does not fit the local details. They depend on the tides to float them into port and out again. The tidal strength and time tables vary in every port. Visitors to Hawaii are surprised by gentle highs and lows that wash only a foot or so over the lovely beaches. In certain bays and inlets along our Atlantic coast, the highs surge up 20, 40 and sometimes 50 feet. Most shores get two pairs of highs and lows in the 24 hour and 50 minute period, which matches the passage of the moon overhead, But the Gulf of Mexico gets only one gentle pair and the tidal rhythm of Tahiti matches the 24 hour solar day.     

Newton's neat global theory might work if an ocean covered the entire world. But the heaving water is moderated by the shapes of the shores, plus some very complex teamwork between rotation and the different ocean basins. This last theory is understandable when you experiment with a basin of water. Give it a slight tilt and watch. how the water rocks like a see saw. This oscillation sloshes up on each side but the motion decreases toward the center of the see saw. The oscillation sways with a natural rhythm. In a large basin it is slower and seems to be gentler because it has to move more water. We can compare these two small models with the great basins of the North Atlantic and the vast Pacific. Their ocean waters are heaved up by the passage of the moon. Their oscillations slosh high along the shores and decrease toward the center of the see saws, out to sea.     

The Hawaiian Islands are out there in the mid Pacific, near where the oscillation of the huge basin is very slight. Scientists think that this is why the tides there are hardly noticeable. A lazy zone at the center of a tidal see saw is called a node and Tahiti is even closer to a node in the Pacific basin. Its tides seem to ignore the pull of the moon altogether and keep a 24 hour daily schedule with the sun  with slight variations.

There are exceptions to every tidal rule, but North Atlantic tides average higher than those of the Pacific. This might be because the natural oscillation sway in the smaller Atlantic basin is about 12 hours. This paces the earth's rotation under the moon. Scientists are not certain, but they suspect that the matching oscillation and rotation periods may give an extra boost to the North Atlantic tides. However, other factors vary the details along every shore.