NOTE: This cache can only be completed at LOW or MID TIDE as the beach is completely underwater at high tide. Therefore, please check the tidal phase prior to your visit.
Fortunes Rocks is a public beach that is very popular in the summer with tourists and local residents alike. Unfortunately, this beach is narrowing and is almost completely underwater at high tide. What is very interesting about Fortunes Rocks is the annual cycle of sand deposition and erosion that occurs here. This cycle is driven by coastal storms and the beach exhibits a lean, sediment-starved winter profile followed by a sediment-rich summer profile. During or after a large storm, this change in beach profile can be also be observed in a matter of days (or even hours if you are crazy enough to be here during some of the nastiest weather conditions).
Nearly all beaches show a seasonal variation in their profile (meaning the shape of the beach from the back dunes or seawall down to the water's edge and the amount of sand on the beach). Beaches generally flatten out and erode in the winter and build back up with sand in the summer, creating berms (hills) on the beach. This is because larger storms and higher wave energy generally occur in the winter.
During storms when wave energy is highest, sand erodes from the beach and is deposited in an offshore bar. This flattens the beach and creates a larger area of shallow water, so waves break farther offshore and the energy from those breaking waves is dissipated over a larger area, reducing erosion. Over time, this sand gets deposited back onto the beach, building it up again. (See diagram of classic summer and winter beach profiles at Biddeford Pool in the photo gallery.)
At Fortunes Rocks, the beach is backed by a seawall, formed from rip-rap (in this case, large boulders of granite). Seawalls are built to protect the property behind them and they create more problems for the beach in front of them in a number of ways. First, seawalls cause a beach to narrow, resulting in a loss of recreational space. As sea level rises, shorelines are constantly migrating landward and as the beach retreats up against the seawall, narrowing occurs until the beach finally disappears. The seawall also cuts the beach off from its natural sand supply, which in part comes from dunes at the back of the beach. Storms that would normally erode sand from the dunes in back of the beach and place it on the lower beach to protect it cannot do so. Therefore, sediment is lost to both the beach in front of the wall as well as down-drift beaches, increasing their erosion rates.
During times of extreme sand erosion, peat may be visible on the beach. This is evidence that the dunes and salt marsh once extended much further seaward than they do today and that the shoreline used to be much further east. As sea level has risen, the ocean has migrated landward. The peat can be identified by its very dark brown color. It may appeared layered and almost “woody” in its appearance.
The purpose of this Earthcache is to make some observations about the current status of the beach. If you follow the logs of other cachers, you should be able to see changes on this beach, both seasonally and after storms. I have personally witnessed a height change of approximately four feet of sand at this location in a matter of days.
From the posted coordinates, you should be able to look northeastward and see a culvert emerging from the seawall. The culvert is located at N 43 25.634 W 070 22.632. This culvert drains water from the freshwater pond across the street (Interesting note: I have been told this is the closest freshwater pond to the ocean along the entire east coast of the U.S., but cannot absolutely confirm that). You may see water from the culvert forming a rivulet and may possibly observe rills in the sand closer to the ocean edge. Rills are striations in the sand that form from water (usually groundwater seeping out of the sand, but in this location can be from the culvert water and/or groundwater depending on the depth of the sand) flowing downward to the ocean. Rills can vary in size from a few inches to several feet in width. They are more likely to form during periods of heavy rainfall and maximum spring low tide (when Earth, moon, and Sun are aligned enhancing the force of gravity on the oceans) than in dry times or at maximum high tide. They are also more likely to form when the beach is steeper rather than flat.
Above the culvert, there are two flat, almost rectangular rocks. See photo of the culvert in the gallery for reference. These rocks are important to note as it may be necessary to use them to gauge the level of sand during your visit.
To log this Earthcache, send an email via my profile page with the answers to the following questions. Please do not reveal any of the answers in your log. The email must be received within a couple of days of logging your find. Any logs not accompanied by an email will be deleted. Also, all geocachers must send their own email to get credit for this find. Do not state in your log that another geocacher is emailing the answers for you because your find will be deleted.
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State that this is the Fortunes Rocks Coastal Geology Earthcache.
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Please state the date, time, tidal phase, and brief weather conditions at time of visit (sunny, light rain, pouring rain, hurricane, blizzard, fog, etc.). Note: Foggy conditions may require you to walk down the beach rather than observe from the posted coordinates.
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From the posted coordinates, estimate the height (in inches) of the culvert above the sand level. If the culvert is not visible, use the two rectangular rocks noted above the culvert in the given photo to gauge how much sand is currently on top of the culvert.
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Observe the “river” from the culvert. Estimate how deep (in inches) the “river” cuts down into the sand. If no river is visible, state that.
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Describe any rills or any other interesting features created by the water flowing out of the culvert. (Again, if you are visiting during a time the culvert is buried, please state that.)
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Look up the beach and observe the shape of the sand from the seawall at the back of the beach down to the water's edge. Describe this shape in your email. Do you see any visible berms (hills) created by the sand on the beach? Are any large rocks exposed in the middle of the beach or is it completely covered with sand? From the background info given, would you classify this as a “winter” profile or “summer” profile? What reasons do you have for this classification? If the profile is characteristically out of season during your visit, what reasons can you suggest for this difference in profile?
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Observe the sand itself. Describe the grains (think about how it feels to touch, the size of the grains, the color of the grains, etc.). Based on your observations, where do you think this sand originated? Your immediate surroundings should provide a clue for this answer.
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With your eye, follow the sand down to the water's edge. Do the grain sizes remain fairly consistent or do you see other types of sediments (gravel, cobbles, etc.) on top of the sand? Are there areas where the sand is a very different color than the majority of the beach? If so, describe the color and the areas in which this color of sand is located.
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Optional: Post a photo of yourself and your GPS with the culvert visible in the background to your log as well as any other photos of interesting features on the beach during your visit.