Welcome to the East coast of Jersey
Here at this part of the coast you can find arround the coastline small sand bars, formed by the current during low tide and washed away during high tide.
Eocene limestone occurs on the sea bed arround Jersey, but limestone is absent from the island itself.
It`s not far to the coastline of France. It`s nearly the closest location between Jersey and Bretteville-sur-Ay in France (which is only about 24 kilometers/14 miles away at the french coast). So here`s much of low and high tide visible.
Through this EarthCache you will learn something about the formation of sand ripple marks and a bit about sandbars
At the posted coordinates you will have to look into the water and see what kind of ripples there are. There are three types of ripple marks.
The could be asymmetrical, symmetrical or (very seldom) fossilized.
Tasks/Questions:
1. Of the three types of ripples listed, which do you think they are? How do you think the nearby coast to France affects the ripple formation?
2. Observe some of the ripple marks at this part of Jersey. Please draw a small sketch of the course of the ripple marks and attach your picture to your log entry.Do you find the ripples in the shallow or deep areas of the sandbar?
3. Please upload a photo picture taken at or near the coordinates. You do not need to be in the photo though it is strongly encouraged.
Please answer the following questions, to your best ability, using the information above. When you feel you have them answered correctly, send me your answers via the Geocaching websites messaging feature, or through email.
Any "Found It" logs without the requirements being sent in, will be deleted. You can log your find immediately and you must also add a picture of yourself or your GPS at the location (compulsory).
What is a sandbar?
A sandbar is, simply, a fully- or partially-submerged ridge of sand or other sediment that is formed by waves carrying the sediment either towards or away from a beach.
The turbulence caused by waves breaking offshore from a beach digs a trough in the sand, and then carries some of that sand forward to the beach, and some backward to form a ridge behind the trough.
Offshore bars
An offshore bar is one that will be hidden below the water at high tide, but as the tide drops it will emerge from the water and become dry until the next high tide.
Normally they will form parallel to a beach, as waves take sediment from the beach and add it to the bar. Some offshore bars will build until they are always visible above the water, even at high tide. These are the called barrier islands.
What are Tides?
Tides are created by the gravitational force of the sun and moon pulling on the Earth. As a result, there is a slight bulge in the ocean, what this means is that while one location is experiencing high tide (the side of the bulge), the area on the opposite side of the planet will have a low tide.
Tides are responsible for 50% of marine energy delivered to the coast. The force of the tide pounding on the coastline can form ripple marks in the sand, which can be best viewed at low tide. Because the Rørvikstranda sandbar has a very slight and gentle slope, they can be observed at practically any point in the day (except at peak high tide, unless you are willing to get your feet wet).
What are Ripple marks?
In geology, ripple marks are sedimentary structures, (i.e.: bed planes of the lower flow regime) and indicate agitation by water (current or waves) or wind. As such, they may be used in statigraphic studies to indicate the original position of strata in geologically complex terrain.
'Ripple Marks', simply defined, are wavy surfaces comprised of regularly alternating ridges of and hollows which commonly form at the contact between water and loose sediment. They are sculptured by current or wave action and can be used to determine the direction of transport and environment of deposition of sediments. These same features can be seen today at most beaches, streams and lake bottoms where waves or currents are active.
Symmetric ripple marks are often located on beaches. They are created by a two way current. This creates ripple marks with pointed crests and rounded troughs.
Asymmetrical ripples are created by a one way current. They create ripple marks with still pointed crests and rounded troughs but which are inclined more strongly in the direction of the current.
At very few locations it is possible to observe cross-bedding in the bedding plane. Cross-bedding can include ripples and dunes or any cross stratification caused by currents.
However, here on the beach you will constantly find ripple marks at low tide as soon as the sea retreats. This is because here, in one of the narrowest places to France, there are particularly large differences between high and low tide. These ripples can be observed until the high tide starts again. With the wave movements of the high tide, the ripple marks are washed away until they become visible again at the next low tide.
You won't have to wade in the water if you don't want to. You can see the ripples clearly from the beach during low tide.
So basically ripples are caused by water or wind moving across loose sand. This causes erosion which carves away rocks and sand.
Digression: What are fossilized sand ripples?
Fossilized sand ripples are made of limestone. Limestone is a sedimentary rock that was originally deposited as fine grained particles that settled to the bottom of a large shallow sea which covered this area millions of years ago.
Special conditions are needed to preserve ripples and to fossilized them:
First of all, there must be an abundant source of sand. The overlying layer of sand must be deposited on the underlying ripples quite quickly or the ripples would be destroyed.. The current of water carrying the sand must deposit the sand and not scour the surface of the layer underneath. And the water level must be continually increasing so that the sand will continue to build up, otherwise it would be eroded away.Also, there must be an abundant source of cement to ‘glue’ the sand grains together and make the sediment harden into rock.
References/Sources: www.britannica.com/science/sandbar www.sciencedirect.com https://biblicalgeology.net/ and wikipedia
To get to the ripple marks, you can park your car close to the street and walk down to the beach. During high tide wading may be required. In that case you may get wet. It's pretty better and safer and worth to visit the location during low tide only.
I hope you enjoyed this EarthCache, and most of all, I hope you learned something new! Enjoy your visit and most of all: have fun!