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Blue Hill Tidal Falls EarthCache

Hidden : 12/10/2007
1.5 out of 5
1.5 out of 5

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Geocache Description:

Tides passing in and out over the shallow bottom ledge under the bridge into Salt Pond in Blue Hill, Maine, create an impressive reversing waterfall effect that is very popular with whitewater boaters.

The tremendous tides cause the periodic rises and falls of the ocean in this area. Tides are caused by the gravitational interaction between the Earth and the Moon. The moon’s gravitational attraction causes the oceans to bulge toward the moon with another bulge occurring on the opposite side. When this bulge is coupled with the shape of the Gulf of Maine the tides become extreme.   Since the earth is rotating while this is happening, two large tide events happen each day.


The reversing salt-water falls occurs under the bridge on Route 175 near Carter Point in Blue Hill. This 100 meter long set of falls is formed when the water rushes through a 20-meter gap between the ledges on both sides of the bridge.  As the salt water passes over jutting rocks under the bridge it causes the "waterfalls" effect.  The reversing falls actually are rapids, which are caused by large boulders and ledges in a narrow passage of water. The boulders and ledges, in addition to the narrow passageway between the bridge cement structures form a bottleneck, causing a rise in the depth of water on the neap side of the falls.  As the tidal current slows, the roar of the water gradually diminishes until at slack tide, for a short period of time, the water under the bridge is like a mirror.  Gradually, the direction of the water changes, the seaweed is swept in the opposite direction, and before you realize it ripples appear with the waves growing in size quickly.


Remember that normally that the water flow to the ocean. At low tide, the Salt Pond empty into the sea under the bridge in a waterfall or rapid. As the tide rises above the falls, the seawater forces its way against the waters flow. The rapids slow to a stop for a short period of time giving the appearance that the falls have reversed.  This process repeats itself twice a day.  Because the water is constantly churning things up at the Reversing Falls it often attracts seals and eagle due to the waters provide abundant food for the animals, that makes visiting this earthcache a special treat.


To log this Earthcache: You must visit the area and answer an earth science question. There is no container or logbook for you to sign just a beautiful and unique natural feature to observe. You must post a photo of yourself and your GPS with one of the water features in the background and then to log this cache you must record the time of your visit as it relates to the tides and what you observe, an example of a log might be, Arrived at 4:30 p.m. which was 1 hour after high tide, and the water was running upstream forming turbulence with wave up to two feet high.  There were several seal fishing at the time of our visit.   Over time as the logs accumulate visitors will realize if they want to have the best view of this tidal falls phenomenon the time that they should visit.   Tidal charts are available at: Tidal Charts you will want to use Blue Hill for reference.


If you enjoy this earthcache you may want to check the Maine Geological Survey located at They have developed a number of information sheets or field localities giving a great deal of information about geologic features. They also have a number of books and maps about Maine’s natural history/ geology that you might find interesting.

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