The Prehistoric beach of Porth Nanven

cot valley porth naven

Cot Valley is a magical place that feels a world away from the hustle of modern life. This beautiful valley even has its own micro-climate. As you walk down towards the V of blue sea enclosed by the valley walls, a stream winds it way beside the road, through sub-tropical plants and past ancient tin workings, towards the sheltered waters of Porth Nanven Cove.

cot valley porth naven

This unusual beach, roughly half a mile from St Just on the Penwith peninsula and Cape Cornwall, holds a secret of its own.

Porth Nanven is also known as the ‘Dinosaur Egg Beach’ because it is covered in ovoid boulders of all sizes. These rounded stones were of course formed by the relentless power of the sea. By years of pounding in the rough Atlantic waters but this process did not occur yesterday. These stones were smoothed by a prehistoric ocean around the same time that the first modern humans were making their way out of Africa to Europe, some 120,000 years ago.

When I first visited this beach a mere 10 years ago at first I didn’t notice that there was anything particularly usual about it, after all in Cornwall we have all been witness to the power of water to smooth and change the face of the rocks of our coastline.

cot valley porth naven

It was only when I noticed that these egg shaped stones were in fact coming from the cliff face that I became a bit confused by the geology. My first thought was that they were the terminal moraine left by a glacier but I had never heard of such a thing in Cornwall. I went home and did a little research.

Porth Nanven beach has in fact what is known as a ‘raised beach’ formed sometime since the last ice age. Also known as a ‘marine terrace’, this raised beach was originally formed during the last ‘inter-glacial highstand’, a period of raised sea levels caused by melting of the ice sheets.

Then, when those extreme sea levels fell again, the beach was left high and dry. During rough seas and very high spring tides the waves can sometimes reach the ancient seabed and wash down some of the rounded boulders on to the modern beach.

This ancient period of interglacial change has become known as the Eemian and recent reports of global warming and melting ice caps have suggested that this extreme tidal variation is something we may come to recognise in the future. . .

Porth Nanven and Cot Valley are now looked after by the National Trust and make a wonderful walk from St Just.

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11 thoughts on “The Prehistoric beach of Porth Nanven

  1. Not “Porth Nanven Cove”, please……’porth’ means ‘cove’ already! But, keep these going, I’m enjoying them.

  2. Lovely little cove with a good view of The Brisons rocks – as seen at the beginning of Poldark!

  3. You say “These stones were smoothed by a prehistoric ocean around the same time that the first modern humans were making their way out of Africa to Europe, some 120,000 years ago/”
    Can you please provide more information (or a link to same) regarding the “prehistoric ocean”? e.g., Given plate tectonics movements, I’d like to understand the configuration of continents & oceans relative to Cornwall “120,000 years ago” Thank you!

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