Blue Point Raised Beach
The last ice age lasted for around 100,000 years. Between 70,000 and 10,000 years ago the whole of the Isle of Man was covered by an ice sheet which had spread out from the mountains of Scotland. The ice over the Isle of Man is thought to have advanced and retreated several times during this period, reaching thicknesses of up to a mile.
Before the ice came, around 70,000 years ago, the whole northern plain of the island didn’t exist. A map of the island before the ice came would have looked something like Fig.1.
As the ice moved forward on its journey from Scotland, it pushed loose stone and gravel in front of it. When the ice retreated it left behind so much material (see Fig.2) that 10,000 years ago the island probably looked something like Fig 3.
The island of today is shown in Fig.4.
Since the last ice age, coastal erosion has taken place and this can be clearly seen between Blue Point and Peel, with the coast near the, once inland, town of Kirk Michael particularly affected. At the same time, what is known as “longshore drift” has occurred, removing pebbles from the coastline which have then been deposited at the Point of Ayre. In fact the Point of Ayre is growing as more and more pebbles are deposited.
So we have a coastline that is eroding in some areas and another area where it is getting bigger. But here at Blue Point we see a different phenomenon:
If you stand at Blue Point today and look east, you can see the evidence. Standing at the posted waypoint and looking inland you will see a line of cliffs covered in vegetation. This ridge appears to have been eroded by the sea, but in fact it is the lower land that has slowly lifted and has pushed the sea back, forming what is known as a raised beach.
These cliffs were once right at the edge of the sea but now they are set well back as the result of something called Isostatic Rebound. When this area was covered in ice it is estimated that it was up to 750 metres thick and therefore weighed millions of tons. The weight of the ice pushed the land down into the earths crust, but when the ice melted and the weight was gone, the land began to slowly rise up again.
The recovery is slow at just a few millimetres a year, so not noticeable, but some geologists estimate it will continue to rise for another 10,000 years. Rising sea levels might mean the process is even less noticeable to anyone around to see it.
Many thanks to Charles Guard for allowing us to use material from his book "The Wonders of Mann", to Dave Burnett for his permission to use material from the Manx Geological Survey and to Jon Wornham at Island Images for the aerial photograph.
To claim a 'find' for this Earthcache you must answer the following questions and send your answers in a message to the owner using the link at the top of the page. You can log your find as soon as you have sent your answers to the tasks. We will be in contact if there is a problem.
1. a) Estimate how far the nearest point of the cliffs is from the posted waypoint.
b) Estimate the height of these cliffs above the raised beach.
2. How was the landscape you see today, formed? Was it formed by erosion of the cliffs or by the area closer to the sea rising above sea level?
3. If you were able to return in 100 years time, do you think you would see more or less of the raised beach? Please give at least one reason for your answer.
4. As you go up the road away from the sea, some of the underlying material which makes up the cliffs is visible where there is no vegetation. Describe the soil or other material that you see. Why is this material here?
We'd love to see your photos which, of course, are optional.