During the nesting season for arctic terns, sections of the beach will be cordoned off to protect eggs and chicks, which are well camouflaged amongst the pebbles. Please observe all signage and keep dogs on leads at such times to avoid disturbing them.
The posted co-ordinates will still be accessible. For your own safety and to ensure you can answer Q4, please avoid attempting this EarthCache in the event of severe storms.
Ayres Lighthouse. Image courtesy of Andy Stephenson
Between 70,000-10,000 years ago the Isle of Man was covered by an ice sheet which had spread out from the mountains of Scotland. Incidentally, here you are closer to Scotland than Douglas, the island’s capital.
Geological cross-section through the northern plain
The ice is thought to have advanced and retreated over the Island several times during this period. When the ice advanced for the last time, it pushed up a pile of soft sediment in front of it to form the Bride Hills. When the ice melted it deposited material contained within it to form a layer of glacial sediment now covering the northern plain. Some of this material includes rock from the mountains of Scotland and from the floor of the Irish Sea and can now be found as pebbles at the Point of Ayre. The word “Ayre” is from the old Norse word “eyrr”, meaning “gravel bank” which appears to describe this area well.
We know some of the stone is from Scotland as riebeckite microgranite, formed during the Paleogene period millions of years before the ice ages, and unique to Ailsa Craig off the west coast of Scotland, has been found on beaches on the Isle of Man.
Fast forward several thousand years and we can see a huge quantity of pebbles at the Point of Ayre which have been dragged up over the years from the beaches on the west coast. Coastal erosion and prevailing winds and tides mean that the stones work their way up to the Point and are deposited here, whilst the sand is washed back out to sea and forms huge banks just under the surface. This process is called longshore drift.
Longshore drift
Longshore (littoral) drift is the movement of material along the shore by wave action. It happens when waves approach the beach at an angle. The swash (waves moving up the beach) carries material up and along the beach. The backwash (waves moving back down the beach) carries material back down the beach at right angles. This is the result of gravity. This process slowly moves material along the beach and provides a link between erosion and deposition.
There is much more energy in the swash than the backwash, so this can move quite large pebbles up the beach. The sand and smaller grains are carried away, back into the sea, by the backwash, leaving a stony beach of similarly sized pebbles and forming sand banks offshore which can affect the waves and currents, causing waves to break offshore due to the shallow water.
A sandy beach typically has a gentle sloping profile, whereas a shingle or pebble beach can be much steeper. The beach profile may have ridges (called berms) formed by different tides.
17th. century map by John Speed
If we look at John Speed’s map of the Isle of Man from the early 17th century, it has some differences from modern maps. Notable differences are more protrusion into the sea above Ballaugh on the west coast and a different position of the Point of Ayre. Of course, aerial views and satellite imaging have given us much more accurate tools in order to produce modern maps. But erosion of the north west coast of the island and deposition at the Point of Ayre means that his surveying was probably much more accurate than it would seem at first glance. Even the 1868 Ordnance Survey map of the area shows a marked difference.
The black line shows the position of the high water mark from the 1868 Ordnance Survey overlaid on a 2016 aerial view.
Further evidence of the shifting shoreline is that as the Point of Ayre moved, the original lighthouse here, built in 1818, engineered by Robert Stevenson and the oldest operational lighthouse on the island, found itself further inland and an auxiliary light, nicknamed The Winkie due to it flashing every 3 seconds, had to be built further east. In time, it had to be moved and increased in height. (After being decommissioned in 2010, it was sold into private ownership. The main lighthouse buildings and land have been in private ownership since 1993 when the light was fully automated).
Please send your answers to the following questions to the CO by either message or email in order to claim a "find" for the cache:
Q1. Walk to GZ via the concrete path and you will pass the auxiliary lighthouse known as the Winkie. (a) Estimate the distance of the Winkie from the original lighthouse. (b) When was the Winkie built and why was it needed? (c) When and why did it have to be moved and the height increased?
Q2. Once at the posted co-ordinates, take a look at the vast shingle beach here. (a) What size are the smallest and the largest pebbles you can see? (b) Is there a large variation or are they all similar in size? (c) What is the reason for this?
Q3. (a) Does the beach here slope gently to the sea, is there a continuous steep slope or are there several slopes and ridges (berms)? (b) Is this typical or unusual for a pebble beach?
Q4. Look out to sea between north and east. Apart from a buoy further to your right, what evidence do you see that longshore drift is forming sand banks offshore?
We would love to see a photo you have taken of the Winkie, perhaps at an unusual angle or with you or your caching equipment in the picture, but we will remove any photos which are "spoilers".