In the last issue of Connecting Albert County, I explained what causes tides. This time, I will explain what causes the tides in the Bay of Fundy to be among the highest in the world.
It all starts out in the Gulf of Maine where the tide from the Atlantic Ocean comes around Nova Scotia counter-clockwise and enters the mouth of the bay twice a day. The distance the water must travel to get to the Hopewell Rocks is about 290 km (180 miles). Out at the mouth of the bay, the bay is about 100 km (62 miles) wide and 213 m (700 ft.) deep.
Ahhh! But it does not end there because there is another key reason for the high tides and that is something called the “seiche effect” — the resonance that the Fundy tide has with the Atlantic tide because of the shape and length of the bay.
There is a fortuitous coincidence in the timing of our tides because it takes our tide an average of 6 hours and 13 minutes to come all the way in the Bay of Fundy (or go all the way out). The result is that the departure of tide water from the Bay of Fundy coincides with the arrival of the next high tide from the Atlantic. The ebbing tide meets the flood tide which raises the water level as the flood tide pushes up the bay. The water “stacks” up on the remaining water in the bay as the water progresses up the bay, rising even more as the bay gets more shallow and narrow.
So there you have it: the combination of the shape of the bay and the serendipitous timing of the ebb and flood tides are the two main reasons why the Bay of Fundy has one of the highest tides in the world (the other being the Ungava Bay in northern Quebec).
By the way, the vast majority of tides in the world are semi-diurnal (two highs and two lows in a 25-hour period). There are also diurnal tides (one high and one low a day) and mixed diurnal (a mixed bag of all kinds of weird tide times). There are 400 constituents or factors involved in tidal predictions and most tide-predicting or hydrographic organizations use only a fraction of these to develop tide charts.
To learn more about tides, I highly recommend two books: Beyond the Moon (2006) by James Creig McCully and Tides: the Spirit and Science of the Ocean by Jonathan White, which was just released.
NOTE: Jon White will be speaking, answering questions, and signing his book at the Hopewell Rocks on Monday, July 10th at 10:00am. If you are interested, come join us. Local residents wishing to enjoy the presentation should identify themselves to Hopewell Rocks admissions staff and tell them they are here to see the Tides presentation; the admissions fee will be waived.