Double Knotted EarthCache

Double Knotted

Fort Creek Park – Port La Tour

The Fort Creek Park is a great rest stop with views of the Atlantic Ocean, located at the site of Fort Saint Louis National Historical Park. There are no visible remains of this 17th-century French Regime fort, which was constructed during the 1620s. By 1629 Fort Saint Louis was the sole remaining French military post of significance in early Acadia. The English were unsuccessful in their attempts to capture the fort. The site’s landscape now consists of a small grassed area with an HSMBC cairn and plaque surrounded by trees and brush, bounded to the west and to the east by the shoreline’s high water mark. The park is close to the Crows Neck Beach and lighthouse at Baccaro Point.

The Islands

Once you leave the parking area, it is 275 m to the trailhead for the first island. As the tide recedes the path to Gooseberry Island becomes wider and drier to traverse.

Gooseberry  is a double tied island attached to the shore by a sandbar.  It can only be accessed at low tide. On the North-East side of the island is another rocky tombolo that attaches Gooseberry and Sheep Island, which lies to the East of Gooseberry.

To access Sheep Island you can use the tombolo between it and Gooseberry Island. This is a very rocky access that can be slippery and must be done at very low tide to access Sheep Island.

Tied Islands

Tied islands, or land-tied islands as they are often known, are landforms consisting of an island that is connected to mainland or another island only by a tombolo: a spit of beach materials connected to land at both ends.

How are tied islands formed?

A tombolo is formed when a spit connects the mainland coast to an island. A spit is a feature that is formed through deposition of material at coastlines and forms a bar perpendicular to the shore line. The process of longshore drift occurs and this moves material along the coastline. There are many other islands in this area that have helped to slow the waves down and contribute to the formation of shoals, sandbars and tombolos.

True tombolo's are formed by wave refraction and diffraction. As waves near an island, they are slowed by the shallow water surrounding it. These waves then bend around the island to the opposite side as they approach. The wave pattern created by this water movement causes a convergence of longshore drift on the opposite side of the island. The beach sediments that are moving by lateral transport on the lee side of the island will accumulate there, conforming to the shape of the wave pattern. In other words, the waves sweep sediment together from both sides. Eventually, when enough sediment has built up, the beach shoreline, known as a spit, will connect with an island and form a tombolo.

Morphology and Sediment Distribution

Tombolo's demonstrate the sensitivity of shorelines. A small piece of land, such as an island, or a beached shipwreck can change the way that waves move, leading to different deposition of sediments. Sea level rise may also contribute to accretion, as material is pushed up with rising sea levels. Tombolo's are more prone to natural fluctuations of profile and area as a result of tidal and weather events than a normal beach is. Because of this susceptibility to weathering, tombolo's are sometimes made more sturdy through the construction of roads or parking lots. The sediments that make up a tombolo are coarser towards the bottom and finer towards the surface. It is easy to see this pattern when the waves are destructive and wash away finer grained material at the top, revealing coarser sands and cobbles as the base.

Refraction

Refraction is the change in direction of a wave, caused by the change in the wave's speed.  Wave refraction involves waves breaking onto an irregularly shaped coastline, e.g. a headland separated by two bays, or islands. Waves drag in the shallow water approaching a headland so the wave becomes high, steep and short. The part of the wave in the deeper water moves forward faster causing the wave to bend. The low-energy wave spills into the bays as most of the wave energy is concentrated on the headland. This refraction moves particles, and stones and contributes to the erosion of the headland.

Diffraction

Diffraction refers to various phenomena that occur when a wave encounters an obstacle or opening. When a wave meets the edge of an object, you would think some would go straight ahead, while the blocked portion would be reflected or absorbed. But what happens is that right at the edge of the object the wave starts to wrap around the edge. This interesting characteristic of waves is called diffraction. You can see this with a lake or ocean breakwater, where the water waves tend to curve around the edge of the breakwater.

To log this Earthcache visit the viewing location.  Please answer the following questions and send in a timely manner to my geocaching profile or email. Answers not received will result in deleted logs.

Note: Only attempt as the tide is receding or low as you will have to walk across the first island to get answers and make it back with dry feet! Rubber boots or high water proof foot wear may be a good choice. Be ever conscious of the tide.

If visiting in June: There are nesting birds on this island. Please avoid this area during the month of June. Take your picture from the sandbar.

Questions:

1. How wide and long is the tombolo/sandbar leading to Gooseberry Island?

2. Was the tombolo created from a Diffraction or Refraction wave action process?

3. Why did you choose your answer in Question 2?

4. How wide and long is the tombolo leading to Sheep Island?

5. How is the material in the Sheep Island tombolo different from Gooseberry tombolo?

6.  Was the Sheep Island tombolo created from a Diffraction or Refraction wave action process?

7. Why did you choose your answer in Question 6?

8. Which island is larger, Gooseberry or Sheep?

9. How do you think the size of the island contributed to the development of the tombolo’s?

10. Do you see any other geological features that may have contributed to the development of tombolo's in this area?

11. Post a picture in your log with a personal item or hand in picture to prove you were there.

[REQUIRED] In accordance with the updated guidelines from Geocaching Headquarters published in June 2019, photos are now an acceptable logging requirement and WILL BE REQUIRED TO LOG THIS CACHE. Please provide a photo of yourself or a personal item in the picture to prove you visited the site.