The Great Eucrite

The rugged hills that provide the backdrop to villages like Sanna (pictured here), Achnaha, Portuairk and Kilchoan are part of a series of concentric mountain circles in the centre of this end of the Ardnamurchan peninsula. They are made of a rock called Eucrite, a variety of gabbro. Its molten magma cooled very slowly, deep underground, so it formed a very hard rock. This magma also rose higher through the crust to feed a mighty volcano which erupted some 65 million years ago, spewing out runny lava flows which are still found across large areas of the peninsula. That most of the lava has disappeared, and the Eucrite now lies exposed, shows the huge erosive power of the ice which covered this area much more recently.

The Ardnamurchan volcano was active at the same time as volcanoes in Skye, Rhum, Mull and Arran. All erupted at the time that Greenland was separating from Europe. That they are almost in a straight line was probably because they formed along a line of weakness in the crust, though more fanciful theories include a suggestion that they were the result of an impact by a large meteorite which broke up on entry into the atmosphere, its pieces smashing holes in the crust.

The Ardnamurchan igneous complex is world famous, so one group of visitors to the Kilchoan area are the geologists who come to study it. A large party of students from Glasgow University comes each year, staying at the Sonachan. Lone figures, clutching notebooks and a hammer, are common along the foreshore below Kilchoan and Ormsaigbeg during the summer, students doing the 6-week mapping exercise required for their BSc. We also have our resident geologist, Rob Gill at Achnaha, who runs a small business cutting thin sections of rock for use in microscope studies - his website is well worth a visit, not least for the beauty of the colour effects his slides make under a polarising microscope.