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Wednesday, September 30, 2015

The Fundy Bay Tides

Each day 160 billion tons of seawater flows in and out of the Bay of Fundy during one tide cycle — more than the combined flow of the world’s freshwater rivers! 

The time cycle between a high tide and a low tide is, on average, 6 hours and 13 minutes. As such, you can reasonably expect to see at least one high and one low tide during daylight hours.

Tide times move ahead approximately one hour each day, and tide times vary slightly for different locations around the Bay.

Are the Bay of Fundy tides a 50-foot wall of water?

The Bay’s tides do officially measure 50 feet in height but the tidal bore (just one of several ways to see the tides) is not a 50 foot wall of water twice a day. A tidal bore appears as a backflow of water into a river. A tidal bore can be around 10ft tall and people are rafting (or surfing) it.

Here, at the Passamaquoddy Bay, we are seeing an average daily change of about 24ft-27ft (between the tides.

So why are tides different in different areas?

It's not related to latitude. Tides are caused by the gravity of the moon, which pulls the water away from the surface in what is essentially an extremely long-period wave (the period of a wave is the length of time it takes the entire length of a wave to pass a fixed point) that follows the movement of the moon.
I won't get into the more gradual patterns such as spring tides and neap tides, but the differences in the tides that different areas get are actually a function of the geography of the area. As a result, there are two general patterns of tides: diurnal tides, meaning an area that receives only one high tide and one low tide each day, and semidiurnal tides, which are observed in ares that recieve two high and two low tides every day. Also, coastlines that are exposed generally have less difference between high and low tide, while enclosed coastlines like the fjords of Iceland can have up to fifty feet between high and low tides.

Factors such as the depth and breadth of the bodies in which tides occur and the configuration of shorelines affect the tides. Tides are also modified by the friction of the water against sea bottoms.

Today, on September 30, we have a max. high tide of 26.8ft and a low of just 1.8ft.

A local photographer took the pictures below. It illustrates the tidal effects along a building.
lubec landmark001

Lubec Landmark002

2 comments:

  1. Amazing contrast in pictures. Around here we wait for those rare minus tides for clam digging.

    ReplyDelete
  2. We have seen the tides in various areas around the coast of New Brunswick and are sure amazing to watch.

    ReplyDelete

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