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Master Naturalists: Learning about the Bay of Fundy

By By Paul and Mary Meredith
June 27, 2013 at 1:27 a.m.

Tidal extremes in Fundy Basin's sea caves at St. Martins were 26 feet when these pictures were taken.  The first picture was taken at low tide, while walking on the bottom of the bay about 100 yards out from the shoreline.  The caves shown are eroded by wave action against 100-foot cliffs of soft conglomerate and sandstone rocks.

Conglomerate rocks

Conglomerate is the term used for rock that has both a base rock that holds together the whole thing, and also pieces of at least one other, different rock contained within the base rock. For example, it could consist of a sandstone base and have pebbles contained within the sandstone. Sometimes the other rock is quite large, sometimes not. Sometimes it has smooth edges, sometimes not. Needless to say, there are many variations in conglomerates.

Last month, for vacation, we flew to Maine, then drove to Canada to attend a six-day program on the cuisine, history and culture of coastal New Brunswick.

Ending up in the village of St. Martins - located on the shore of the Bay of Fundy - we had a marvelous time; suffering through highs in the 50s and lows in the 40s.

While St. Martins is small (380 residents), the village is old, founded in 1783. It has a rich history as a major shipbuilding and trade center prior to the advent of steamships.

Originally tied to both the lumber trade and the unique tides and currents of the Fundy, St. Martins is now a tourist destination adjacent to the Fundy Trail and Parkway at the head of a 42-mile footpath leading to the boundaries of Fundy National Park.

Fundy's unique nature

Tides in the Bay of Fundy are huge, up to 52 feet twice a day at the northern end, and up to 32 feet in the Saint John/St. Martins area. That got us interested.

We know tides are mostly lunar effects. Our moon pulls up two domes of water as it revolves around Earth every 28 days, and as Earth revolves daily. These two domes are on opposite sides of Earth, meaning most spots on Earth where tides occur get a high tide about twice every day.

One high tide results because the ocean closest to the moon's location is pulled up toward it by the moon's gravity. And the other dome (tide) half a world away, on the opposite side of Earth, occurs because Earth itself is pulled away from the oceans by that same gravity.

Our Gulf's tides are small - 1-2 feet. Why are Fundy's tides so large? That's all in the geography - Fundy Bay is long and narrow, shallow at both ends and deep in the middle.

The shape causes tides to slosh up and down the bay, sucking Atlantic waters in at high tide and flowing back out to a lower Atlantic on a low tide.

Fundy's formation

How old is the bay? Not very - only about 15,000 years old, according to hydrologists studying the end of the last ice age. A long time (350 million years) before that, it was formed as a deep "rift" valley - a crack - in Earth's crust when Africa's continental plate split off from North America's and slid south to its current location.

Fundy is northernmost of 12 rifts along North America's eastern coast. It was not originally connected to the Atlantic, which formed as the continents split. With no ocean connection, Fundy's inland sea water eventually evaporated as Great Salt Lake in Utah is doing now.

Climate changed to wetter 320 million years ago. And nearby mountains eroded, filling the rift bottom with conglomerate, layers of large rocks smoothed by water. Five million years later, jungle conditions deposited thick layers of coal and shale in the rift.

Much later - 210 million years ago - the rift was volcanically active, and the land was up-thrust, and folded under tremendous pressure. The land later tilted, forming what would become the bay's mouth after glaciers scoured out the rift over the last million years, forming the escarpments/cliffs seen today as living, 350-million-year geologic history of the region.

About 15,000 years ago, glaciers melted, raising the level of the Atlantic to above the land level at Fundy's mouth. The Atlantic broke through, flooding the eroded rift, forming the current tidal-bay system.

Really good result

One side effect of Fundy's twice-daily, multibillion-gallon tidal sloshing effect is that warm water from the south constantly mixes with bay water, holding water temperatures around 50 degrees year-round - perfect for producing delicious lobsters, salmon and scallops that we consumed in abundance.

Sources: Tides of the Bay of Fundy, http://www.classzone.com/books/earth_science;

http://www.fundytrailparkway.com;

Quaco Historical & Library Society, http://www.quaco.ca;

Geological Formation of the Bay of Fundy, http://bayoffundy.com/articles/geological-formation;

Eastern North America Rift Basins.jpg, Source NASA, in Geological Society of America, vol.268, pp.279-308, 1992

Paul and Mary Meredith are master naturalists. Contact them at paulmary0211@sbcglobal.net.

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