CYMRAEG search COVID-19 (Coronavirus) For details on service changes visit our Coronavirus information and advice page. VOLCANIC HISTORY Home / About the National Park / Geology / Volcanic History SHARE THIS You will often hear it said that isolated craggy hills like Carn Llidi and Penbiri near Whitesands Bay or Garn Fawr on Strumble Peninsula are the eroded remnants of old volcanoes. Whilst there is an element of truth in these statements – the rocks did indeed form when molten rock cooled and crystallised – there is no relationship between the form and rock type of these hills with those of actual volcanoes. These great rock masses seen in the National Park were originally magma that cooled and crystallised at varying depths, within a great thickness of mud and ash that was accumulating in a deep basin on the sea floor. The highest hill on Ramsey Island, Carn Llundain, certainly looks like a volcano, but you’re going to be very disappointed if you expect to find a smoking crater at the top (never mind, the view from here is possibly the best in Pembrokeshire). The inclined layers of rocks that underlie this hill are mostly thick accumulations of ash and larger fragments that accumulated on the seabed during very violent underwater eruptions. So not a volcano at all! VOLCA-NO? They’re therefore not remnants of extinct volcanoes, but igneous intrusions – mostly sills, formed when molten rock pushed and melted its way between other layers – that have subsequently been exposed by weathering and erosion. The slow cooling of the mostly basic magmas led to the development of large crystals, which would not be present in a rock formed from an outpouring of lava. CONTINENTAL DRIFT Another important thing to consider is that these rocks were formed around 470 million years ago, and in a location comparable to the present position of the Antarctic Peninsula. At that time the configuration of continents bore no relation to those we see today. These rocks have reached their present position (around 9,000 miles from where they began their journey) by the process of continental drift (movement of the ‘plates’ that make up the Earth’s crust). What we see today is a small fragment of an ancient ocean floor that has been fitted into the mosaic of rocks that is now Pembrokeshire. During this time there is also ample evidence of volcanic activity, but it mostly occurred as submarine eruptions, although occasionally enough material may have accumulated to form a volcanic island. PILLOW LAVAS Much of the area around Strumble Head is composed of pillow lavas. These basalts erupted relatively passively in deep water. So although Pembrokeshire’s spectacular landscape is indeed the result of volcanic activity, we can’t quite claim to have Tracey Island style volcanoes or craters. However thanks to the volcanic activity, we have been left with a rich geological landscape that is every bit as exciting and dramatic as any episode of Thunderbirds. MORE ABOUT THE NATIONAL PARK'S GEOLOGY GEOLOGICAL LANDSCAPE Pembrokeshire’s landscape is forever being photographed and painted, appreciated by the walker and artist alike. But what has created this landscape... READ MORE ON GEOLOGICAL LANDSCAPE GEOLOGICAL CONSERVATION Forget castles, Iron Age hill forts, golden sandy beaches and the ice cream van. We’re talking about what’s under your feet! The very stones on wh... READ MORE ON GEOLOGICAL CONSERVATION CLIMATE CHANGE What do us Brits like discussing more than anything else?! The weather of course! From tropical landscapes to glaciers and ice sheets, Britain has bee... READ MORE ON CLIMATE CHANGE GET IN TOUCH Contact us and register your details to get the latest updates on what's happening in the Pembrokeshire Coast National Park. CONTACT US National Park Office Llanion Park Pembroke Dock Pembrokeshire, SA72 6DY Tel: 01646 624800 Email: info@pembrokeshirecoast.org.uk VISITING Plan your visit Access for All Carew Castle and Tidal Mill Castell Henllys Iron Age Village Oriel y Parc Gallery and Visitor Centre QUICK LINKS About the National Park Authority About the National Park Planning Contact Us News Jobs Accessibility Statement Privacy Policy Terms & Conditions Cookie Policy Sitemap © 2021 Pembrokeshire Coast National Park. We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. By clicking “Accept”, you consent to the use of ALL the cookies. However you may visit Cookie Settings to provide a controlled consent. Cookie settingsACCEPT