Saint Peter and Saint Paul Rocks
A geological mystery.
This describes the remarkable and isolated Saint Peter and Saint Paul Rocks. These lie far from land in the Equatorial Atlantic Ocean.
When the Air France AF-447 crashed into the Atlantic on 1st June with the loss of all passengers and crew it set me thinking. This loss must have occured within 1000 miles or so of extraordinary archipelago of Saint Peter and Saint Paul.
I first read about these rocks in Rachel Carson’s excellent book The Seas Around Us. Rachel Carson comments that the entire cluster of islets is no more that a quarter of a mile across. At their higher point the rocks rise 59ft (18m) from the sea. The largest rock is vegetated with moss and grass. The other rocks are almost barren, only algae and fungi that can tolerate the salt spray. The rocks are inhabited by seabirds. crabs, insects and spiders. There is no permanent fresh water.
Rachel Carson observes that the rock slopes drop off at so sheer an angle that the water is more than half a mile deep within a few feet of the shore.
Image via Wikipedia
The Seas Around Us was first published in 1950, Since then earth scientists have learnt a great deal about the rocks. Geologists know that the rocks are composed of dark green rock known as peroditites. These are very ancient rocks. Radio carbon dating indicates that they are older than the 4.6 billion year age of the earth’s crust. Peroditites are formed many miles below the ocean crust in the mantle. This archipelago of the Rocks of St Peter and St Paul is is the only place in the world where the abyssal mantle is exposed on the surface. It is the surface manifestation of a gigantic tear in the oceanic crust.
I find this extraordinary. Rocks older than the sea floor have formed a seamount over 2 miles high.
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3 Responses to “Saint Peter and Saint Paul Rocks”
On July 22, 2009 at 4:53 pm
Cool article – not a place I will book for my next holiday but good to know it’s there!
On July 23, 2009 at 11:58 am
Thanks for your complement. I am intrigued by this place though it doesn’t get much publicity.
I think these are the oldest exposed rocks in the world – even though the text books say the oldest are in Canada or Australia. I also think that the mechanism behind their formation has big implications for plate tectonics..
I haven’t got space to explain this here. Maybe, I’ll do another article.
On August 16, 2009 at 7:53 pm
This is interesting. I’d like to read more of your articles like you mentioned above.
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