On the Rocks

The rocks that we see on Islay give us access to a mind-blowing and grandiose history of the planet. The timescales we’re dealing with are the last 1.8 billion years - reaching halfway back to the very formation of the earth. There is evidence on Islay of unrecognisable continents, past glaciations, the beginning of life on earth, and the vestiges of the much more recent ice age just a few thousand years ago.

We’re interested in the geology for three reasons. One, its direct bearing on agriculture - the different soils that the bedrock gives us affect the successful raising of barley here. Two, what the geology means for the water we use to make whisky. Three, it deepens our understanding of Islay's terroir - several rock types and aeons collide here.

SIMPLIFIED MAP - BRITISH GEOLOGICAL SOCIETY

Loch Gruinart and Loch Indaal are two shallow sea lochs that divide Islay from the north and south. They were formed along a branch of the Great Glen Fault that divides Scotland, the same fault system that creates the famous national landmarks of Loch Ness and Glencoe as it travels from north-east to south-west. It also produces the minor earth tremors that occasionally rattle our windows! Along the faultline in the middle of Loch Indaal, around 470 million years ago, two super continents collided after the closing of the ancient Iapetus sea which separated them. Scotland had been on one super-continent, England on the other.

You can see the drama written into the tilted rocks in the Port Ellen area. David Webster, who had a career in the oil industry before retiring to Islay - where he has built a house behind the distillery and written a book of geological walks - remarks, “If they drained Loch Indaal, they’d probably find dinosaur fossils down there off Port Charlotte! The scallop dredgers have turned up ammonites from the same era…”

THE ROCKS OF THE RHINNS

The most famous of the local rocks to Bruichladdich are ancient gneisses. They were formed as part of a volcanic arc connecting Labrador, Greenland and Scandinavia, with Islay somewhere in the middle, 1,800 million years ago. They are known throughout the world as the Rhinns Complex.

These once igneous rocks, formed deep beneath volcanoes, have been metamorphosed, under intense pressure and heat, while buried maybe 50 kilometres down in the earth’s crust. The Rhinns' many fault lines have led to their exposure. On the shore at Bruichladdich, just outside the distillery, you can see pink-hued ex-granite so coloured because of the potassium feldspar in its mineral mix, and a green ex-basalt containing hornblendes. Green and pink pebbles are very common on the beaches of the Rhinns.

There are places in the Rhinns where these ancient metamorphic rocks butt up against a type of sandstone that has also undergone metamorphism. These meta-sandstones are 800 million years old, pre-dating the explosion of life on earth. Where the junction of these two types of rock is on the coast, the waves have cut a cleft along the fault line – like at Kilchiaran – so there's a visible ‘billion-year’ gap.

OVERVIEW OF THE REST OF ISLAY

In the north of Islay, around Bunnahabhain and Bolsa, there are 650 million year old limestones that contain fossilised mounds of algae that were earth’s first multi-celled lifeforms. Thick beds of dark grey limestone, slightly older than that at the coast, occur around Ballygrant. That is where the lime for improving the fertility of Islay’s fields is quarried and ground.

55 million years ago, just after the extinction of the dinosaurs, the Atlantic ocean was formed along where the earth’s crust tore between North America and Eurasia - the northern shore of Islay is the place to see evidence of that event, where there are “enormous vertical sheets of frozen magma, called dykes.”

GLACIATION

There is a tillite bed near Port Askaig that provides evidence of an early Ice Age, but Islay was also ice-covered during the recent Pleistocene glaciations when the island marked the edge of the great northern ice sheet. The complex changes of sea level due to melting ice caps since then have left a series of "raised beaches" around the coast. The last of these great changes probably happened less than ten thousand years ago.

Throughout much of late prehistory, when humans were using stone tools and beginning to farm, the low-lying land between the Rhinns and the rest of the island was flooded, creating two islands that have only recently become one. It is possible that Loch Gorm, a few miles west of the distillery, is a “kettle hole” where part of a glacier was trapped with rocks and mud on top of it, later melting into a “boggy hollow” (David’s words). The fields surrounding the Loch at Ballinaby and Rockside are underlain by gravels and sands deposited by rivers coming from the melting glaciers, giving them good drainage and better soils for growing barley for whisky-making.

THE OCTOMORE SPRING

Because we are one of only two distilleries who bottle all our whisky on Islay, there is an additional geological feature in play in our finished products - our use of local spring water. Our bottling water bubbles out of the mind-bogglingly ancient rock tapestry of the Rhinns. The spring’s local name is Tobar an Uisge Fhìor – “the well of the true water”. It is on Octomore Farm’s land. The Octomore spring water has also been analysed by the University of Stockholm. It is, “Nothing like the surface water,” confirms David. It was found to contain silica at a concentration of 17 parts per million. This is unusually high and unlike any other water on the island. So the water carries a piece of Islay's geological inheritance to every corner of this modern, whisky-drinking world. Savour it. It took hundreds of millions of years to make.

With thanks to David Webster for the pictures and the facts.

FURTHER READING

A Guide to the Geology of Islay: Webster, Anderton and Skelton. (2017): Ringwood Publishing Glasgow

David’s video presentation on Islay's Geology for the Royal Philosophical Society of Glasgow