Nancy Boren, age 12, of Cooksville, Ontario, Canada, for her question:
What is the tidal bore in the Bay of Fundy?
The heaving might of our restless ocean is one of the most powerful forces of our planet. On a small scale, it creates the tricky rip tides that threaten careless swimmers off certain beaches. On a larger scale, the heaving waters create overwhelming tidal bores.
For ages mankind has clocked the rise and fall of tides in bays and docks and along shores around the world. This daily schedule with its countless variations is so well known that most tides can be predicted way ahead of time. Modern scientists, however, want to know more of these events. They view all tidal activity on a global scale in order to explain the wide variations in terms of global patterns. Every calendar day, of course, a parade of two high tides and two low tides follow the moon as it passes overhead around the world.
We would expect the tidal ocean to rise and fall to the same levels at every point around the world. But this is not so. The world oceans seem to rock like water in a massive tank. The mid Pacific Islands have tidal changes of only a few inches. They are thought to be in a lazy trough of rocking world ocean water. The Bay of Fundy opens its big mouth where the ocean tides reach a high heave in this global pattern. More tidal water runs in and out.
Other geodetic patterns help to make Fundy Bay's 50 foot tides the highest in the world. Advancing tides meet resistance when they bash into a shore line and the shape of each shore turns the tidal flow in a certain pattern. Fundy Bay acts like a funnel 180 miles long with a mouth 60 miles wide that dwindles to a width of 30 miles. It divides Nova Scotia from New Brunswick. High tides sweep towards these Atlantic shores with great force. To some extent, the heaving water is abetted by strong ocean currents. The smoother shoreline resists the mighty tide and much of the rising water is diverted into the funnel of Fundy Bay. The funnel fills and empties twice each calendar day, with the two sets of high and low tides. The most dramatic upheavals come with the spring tides, the monthly and yearly highest high tides. At such times the water rushes into the funnel at 15 miles per hour in an advancing wall six feet high or more. This event is called a tidal bore. In a few hours, the receding tide has drawn back, draining the bay and leaving ships stuck in the mud at their docks. No matter, in a short while the next high tide will come sweeping in to launch them.
Certain shorelines along Argentina, Alaska and France have funnel shaped inlets that invite high tidal bores. The world has six or so regions where 30 foot tides are expected. But the Bay of Fundy happens to be situated at the crest of a rocking ocean pattern. This global motion sways on schedule. At Fundy Bay, it heaves on a 12 hour schedule that tallies with the tidal motions caused by the moon.