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This earthcache bring you to a wilderness section on New Brunswick’s coast where the forces of nature has formed a tombolo or tied island. We will examine evidence of those forces preserved in the stones of the beach.
The natural history of this wilderness area comes in three parts. First the continental collision forces caused the igneous activity in the area creating what is now called Martin’s Head. Then the glacier took their turn covered and moved over the land shaping the rock bound coast into the smooth rocks that forms the till for the beach which filled in by the forces of the longshore currents that flow along the coast creating this tombolo or tied island. Finally recent storms have put the final touches to the beach face that we see before us today.
The sand bar along the western end breaks the large, smooth volcanic ledges surrounding the island, where currents have deposited sand and stones connecting it to the main-land, this sand bar is known as a tombolo. A tombolo (Italian, from Latin tumulus – mound) or sometimes ayre (Old Norse Eyrr – gravel beach) is a deposition landform in which an island is attached to the mainland by a narrow piece of land. Once attached the island is then known as a tied island. This has formed because the island causes wave refraction, depositing sand moved by longshore drift in each direction around the island where the waves meet. At most tides, a wide sandbar connects the island to the mainland. The island is most accessible at low tide. The tied islands, or land-tied islands, as they are often known, are really a type of peninsula where the island is only connected to land by a tombolo - a spit of beach materials connected to land at both ends.
The stones on the beach are neatly arranged in a series of flat-topped deposits, called storm berms that are stacked on each other. If you look at the beach carefully you will see that each berm has a steeper lower slope, a flatter upper slope, and a line of seaweed and other debris maybe found along its top edge. The next higher berm then repeats the shape: steeper lower, flatter higher, with debris on top. A straight-on view of the beach face shows another interesting feature. In the lower, steeper part of each deposit the stones are slightly smaller than the stones in the upper, flatter part of the deposit. Then, above the line of seaweed, the lower part of the next deposit again has smaller stones. The differences are subtle, but consistent all along the length of the beach. Furthermore, the stones on the steeper, lower slope are quite round, whereas there are several flat stones on the flatter top area.
Each storm berm represents a deposit from a single storm. As the waves break, they release enough energy to scour rocks from the base of the beach and throw them up on the shore. As the tide increases, the waves reach higher and higher levels, pushing stones, seaweed, and driftwood up the beach. As each wave crashes it propels large and small stones up the beach, but as it recedes, it has less energy and can only pull the smaller and rounder stones back down the slope. In this way, the larger, flatter stones are sorted out from the smaller, rounder ones, ending up at the top of the deposit. As the height of the storm passes and the tide begins to fall, the large stones and floating seaweed are stranded at the height of the deposit.
If the next storm is larger than the first one, then the older berm will be wiped out and the stones will be re-formed into the new one. Only the deposit from the largest storm will be preserved. On the other hand, if the next storm is smaller than the first one, only the lower part of the first berm will be affected, and the upper part will be preserved. In this case, the younger, lower berm will rest partway up the older, higher berm. On this beach we found that there were at least four berms preserved, with the highest one being the oldest, and the lowest one being the youngest. Most storms of the magnitude to create berms occur in the winter months. The highest beam maybe be years old and reflect the more violent storm the beach has ever seen.
So what does the beach tells us? First the continental glacier originally deposited the stones that now make up the beach here. Then the waves acting on the glacial deposit washed the mud and sand into deeper water, leaving behind a "clean" deposit of stones. Over time, as the stones have rolled up and down the beach, they have become rounded and polished. Solid bedrock anchors the end of the beach, keeping the stones in a pocket. The shape of the beach changes when storms rearrange the stones on the beach into berms. The largest storms reconfigure the entire beach, whereas smaller storms may only affect the lower portions. Each storm is unique so it leaves a characteristic berm shape, with a lower sloped beach and a higher flatter top. Beaches are dynamic systems that are continually changing.
It is best to visit this earthcache during low tide, that way you will see the greatest development. Because this beach is facing south where the storm approach the beach there are often many berms as evidence of past storms. The top represents the worst storm in the past while each smaller berm represents smaller storms. To log this Earthcache send an e-mail to difference in height of the two worst storms. This will be the difference in height between the two tallest berms. Please begin your e-mail with the name of the earthcache and make sure your log includes the number of people in your group. It also would be nice if you would post a photo so others would know what they have to look forward to at this earth cache.
Additional Hints
(Decrypt)
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