Geoscience Reference
In-Depth Information
Bay of Giant Tides
Where the Gulf of Maine ends and the Bay of Fundy begins is difficult to say, though Canada and the United
States draw a national marine boundary near Machias Seal Island, each nation claiming this seabird republic
for its own. But there can be no doubt that the best place to appreciate the power and volume of the Fundy
tides is Cape Split, an imperious 100-meter-high (300 feet) headland overlooking the entrance to the Minas
Basin in the inner Bay of Fundy. Here, a volume of water equal to the Gulf Stream, or two thousand times the
discharge of the St. Lawrence River, must squeeze through the 5-kilometer-wide (3-mile) Minas Channel. It
does so under furious protest, creating huge standing waves, eddies, and whirlpools that resound and reverber-
ate at the base of the cliffs as the tide floods into Minas Basin, where it can reach a height of 16 meters (50
feet) or more—the highest in the world.
As most of us have been told, the moon's gravity causes the tides, but not simply by lifting the waters of the
Earth. The Earth responds to the gravitational pull of the moon, in effect, by falling toward its celestial neigh-
bor. The waters on the side nearest the moon, being closer, accelerate more quickly than the Earth itself. For
the same reason, the Earth falls more quickly toward the moon than the waters on the far side, so that the Earth
is being pulled away from these waters. The result is that two tidal bulges are produced on opposite sides of
the Earth. As the Earth rotates under these bulges, it produces the twice-daily, or diurnal, tides typical of the
world's oceans.
