Greater Sark and Little Sark are connected by a causeway, a small strip of land, known as La Coupée. It is a high ridge 80 metres (262 ft) above sea level and 100 metres long. The width is about 3 metres.
Some background history about La Coupée.
Up to the beginning of the 20th century is was rather difficult and also scary to access Little Sark. To cross La Coupée meant walking across this very high and windy strech of dirt track with no barriers or handrails on either side. It is said that children have had to crawl on hands and knees to cross safely during high winds.
In 1875 someone wrote: “People have thrown themselves flat on their face, from terror and nervousness on reaching the Coupée; others have lost courage half way across, and have hidden themselves behind the heads of the rocks that crop up in the middle of the Coupée until some passer by came and led them along; others have been unable to get across without shutting their eyes and being led between two persons.”
Already for a long time arguements rose up frequently between the inhabitants and the Seigneur over who was responsible for the maintenance and safety of the path across La Coupée but nothing solid came from these arguements. It wasn't until well after a deadly accident on September 4th 1802, when Elie Guille was blown over the east side while carrying sheaves of corn, and the fact that in 1811 the path was no more than 3 feet wide that in 1812 an act of agreement was signed between the inhabitants and the Seigneur that the maintenance was to be done by the inhabitants and the Seigneur was to guarantee to provide all needed expenses.
In 1862 a retaining wall was created to provide a solid foundation for a roadway between 8 and 10 feet wide (see the photo below).
But is was not only the narrowness of the path and the steep drop on both sides that made many people scared to cross La Coupée, especially at night. But the area was also reputed to be haunted. People spoke of strange moaning sounds or unhuman shrieks. The official explanation for these sounds is that the tidal and wave actions in La Caverne des Lamentes in the bay is creating this sounds, not any type of ghost or spirit.
Protective railings were only added to La Coupée in 1900 and in 1945 a concrete road covering the full length of the istmus was build under the directons and watchfull eyes of the British Royal Engineers by German prisoners of war.
An 1880s photograph by Jersey photographer Philip Godfray depicting La Coupée
Isthmus geology
This type of landform is called an isthmus. An isthmus is defined as a narrow strip of land, connecting two larger bodies of land, with a body of water on either side. They can be of varying size, length and width. Two of the most famous isthmi are the isthmus of Panama and the Sinaï peninsula.
An isthmus can be formed through various geological processes:
1) Vulcanic activity and tectonic plate movement
The lithosphere is made of rigid plates that move atop of the asthenosphere. When they collide tectonic uplift can take place, which can be associated with isthmus formation. A collision can also create vulcanic activity that in turn also may be associated with the formation of an isthmus.
2) Deposition
Deposition can occur through various means. For example wave and tidal action can deposit a sandbar between a coastal island and the mainland. If this is the case, the isthmus is called a tombola.
3) Erosion
Erosion is opposite of deposition. It is the process where material is moved or removed from a solid surface. The main causes for erosion are wind, water and ice, but other, more rare means of erosion, for example volcanic activity or large impact are possible as well.
It is not actually the wind or the water that causes the erosion, but the abrasive particles that it contains, i.e. dusty wind and muddy water. Suspended particles of rock and soil in the water or air indicated that erosion has taken place and is called sediment.
Physical erosion is the physical, but not chemical change of rocks. This often causes the rock to become smaller or smoother. Clastic sediments often contain rocks that underwent physical erosion and were transported from their original place of origin. Physical weathering can take the form of a landslide, where rocks are dislodged from a slope and tumble (and crumble) down a hillside.
3.1) Erosion by water
Liquid water is the main cause of erosion on Earth.
Rainfall has four types of erosion;
- Splash erosion, caused by the impact of a falling raindrop, which can scatter small particles.
- Sheet erosion, caused by runoff (overflow of fluid)
- Rill erosion, caused by runoff that develops into rills (small streams)
- Gully erosion, caused by large channels of water that carry away particles. Gullies appear relatively briefly during times of rainfall or snowmelt.
Valley erosion occurs when flowing streams and rivers wear away their own banks, creating larger and larger valleys.
Coastal erosion wears away earth, rocks and sand on the beach, due to the huge force of the ocean. It has the ability to change the shape of the coastline. Wave action causes friction between rocks, pebbles and sand, grounding them into ever smaller particles. Waves and currents can transport the particles away from the shore. Of course the force of the ocean also causes cliffside erosion and creates a multitude of coastal landscape features. Erosion can bore holes that eventually turn into caves, which can turn into an arch when the back of the cave gives way to erosion.
3.2) Erosion by wind
Wind erosion is of two primary varieties: deflation, where the wind picks up and carries away loose particles; and abrasion, where surfaces are worn down as they are struck by airborne particles carried by wind.
abrasion
Deflation can be divided into three categories:
- surface creep, where larger and/or heavier particles slide or roll along the ground
- saltation, where particles are lifted for a short height and distance, and bounce and tumble across the ground surface
- suspension, where very small and light particles are lifted into the air, and are often carried for longer distances.
deflation
3.3) Erosion by ice
This usually takes place in the form of glaciers. They erode away the earth, creating basins and steep sided valleys. As the glacier moves, it pushes forward everything in its path, from tiny sand particles to large boulders. The rocks that are carried by the glacier scrape agains the ground underneath the glacier, eroding away both rock and soil. This is called plucking. The sediment that is carried away that surrounds a glacier is called moraine.
Thermal erosion entails the erosion of permafrost as the temperature increases. The temperature difference causes the ice rich permafrost to break off in large chunks from the coastline or a river bank.
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Question 1:
Look down from the path in westerly direction to the beach below. What evidence of erosion do you see on the slope and on the beach? What type(s) of erosion do you think caused this and why do you think that?
Question 2:
Referring to the answer to question 1; when this/these type(s) of erosion continue at this location and without human interference, what will happen with La Coupée over time and why?