This EarthCache takes you to St. Ouen’s Bay to visit the widest white sand beach of Jersey.
The EarthCache listing teaches you about the formation of white sand and and how the beach is preserved through coastal protection.
Tasks:
1. Explain in your own words how the beach is being eroded. Will the erosion go on?
2. Describe the beach as you see it. Use the four sections as in the description.
3. Observe the waves approaching the beach. The wave direction (predominantly from the West or South West) will not always be the same and will be determined by the winds out at sea. Do waves hit all parts of the beach equally or do the waves compensate for each other in recurring areas of the beach? What impact do these strong waves have on this part of the beach? (A little help: look at the surfers. Are they in the sea over a wide area or are they concentrated mainly on a section of beach?)
4. A picture of your team, your mascot or GPS at St. Ouen’s Bay is mandatory.
Earth Science Lesson
Geologically, the Channel Islands are peak remnants of the Armorican Massif and consist primarily of plutonic rocks (0.4 to 2.6 billion years old). They became islands after sea levels rose after the last ice age around 10,000 years ago.
Erosion formed the current surface shape: Jersey is a flat plateau with high coasts; in contrast to the islands of Guernsey, Alderney and Herm further north, which slope from south to north.
St. Ouen’s Bay is a White Sand Beach at Jersey.
With mile after mile of beautiful sand, cleansed twice a day by Atlantic waves, St. Ouen’s Bay is probably the most visited white Sand beach because of it‘s pure white sand. The Bay is also a home for surfers.
Take a look around and I'll tell you something about building a beach.
At first glance, the sand looks like a large soft mass - in fact, it is made up of grains that the sea grinds together to make finer grains over thousands of years. Constructive waves add material to the beach, whereas destructive waves (under storm conditions) can carry the grains away.
The wavelength of the waves determines, from which depth of water sand is washed to the beach. In Jersey this can be over 50 meters, and they dig much deeper than short waves. Whether the beach is constructed of coarse or fine sand is determined by the slope on the seabed off the coast. The lower the inclination, the smaller the stones. The current throws the stones to the shore, rubbing them there even finer and smaller, to grains of sand with a diameter of 0.063 to two millimeters.
The type of rock or mineral finally decides what color the beach is: In Jersey, the beach is made of crushed remains of coral and shells. The white dream beaches are made of lime.
No matter what color it has, a sandy beach always looks the same. The beach is constantly changing: waves are breaking over it, wind, rain and sun are acting in on it. And even the most beautiful beaches are changing due to erosion.
The four sections of most beaches
Swash zone: is alternately covered and exposed by wave run-up.
Beach face: sloping section below berm that is exposed to the swash of the waves.
Wrack line: the highest reach of the daily tide where organic and inorganic debris is deposited by wave action.
Berm: Nearly horizontal portion that stays dry except during extremely high tides and storms. May have sand dunes.
Erosion at St. Ouen’s Bay Beach
Types of erosion are:
fluvial erosion - e.g. rivers cutting their own valleys
aeolian erosion - wind blowing away sand and dust
marine erosion - caused by surf and breakers
Sustainable Coastal Development policy in Jersey
This policy explicitly addresses the coastal area as a system that has natural and human aspects and components that are inter-related and dependent on one another. Year after year, large parts of the few beaches are eroded away by erosion, waves and wind and washed into the sea. Effective coastal protection here on St. Ouen’s Bay Beach should counteract this.
The coastal protection measures used are intended, on the one hand, to protect low-lying, human-used areas near the sea from flooding during storm surges (flood protection), but also to protect the coasts themselves from bank retreat and land loss, including due to sea level rise due to climate change.
Causes of storm surge water levels include wind build-up and tidal movement. In coastal areas, these phenomena are overlapped by the periodic water level fluctuations of ebb and flow. The tidal range off Jersey is the third highest in the world. At times when the tide changes are strongest, it reaches an incredible 12 meters.
But there is also natural coastal protection, in which large granite boulders or granite rocks are placed to act as breakwaters in vulnerable places near the shore.
In doing so, they break the incoming waves and thus reduce the pressure on the beach and the mainland.
Where the sand is quickly washed away and there are not sufficient quantities of stones to break the waves, concrete is used as a breakwater. A lot is being done for coastal protection in Jersey. Let's hope that this will preserve the beautiful white beach at St. Ouen’s Bay.
You are welcome to log your answers straight away but please message or Email me with your answers. I'll let you know if anything is unclear. Please don't forget: the answers must be received within 10-14 days or the log may be deleted.
Enjoy your stay – and if you are a surfer, too: enjoy your ride
Source references:
https://www.gov.je/Environment/SeaCoast/Pages/ICZM.aspx
https://www.jersey.com/inspire-me/inspiration/breathtaking-beaches-of-jersey
https://de.wikipedia.org/wiki/Kanalinseln
https://de.wikipedia.org/wiki/Küstenschutz