A chance meeting on the Highland Chieftain train from London to Inverness led to this article coming to light, never been published until now and it is now showing on
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THE CATASTROPHE THAT WAS THE MAKING OF INVERNESS – THE HUB OF THE HIGHLANDSInverness is certainly well situated to be the capital of the Highlands. But have you ever wondered why the city has grown up where it is, at the mouth of the Ness? Why not at Beauly or Dingwall, for example? The answer lies in a remarkable – and scarcely-known - catastrophe which struck this spot 10,000 years ago.
Some while back, it dawned on me that there was something very odd about the geography of Inverness. Here we have a vast extent of flat, easily-developed land on the shores of the Moray Firth, crossed by a big river to make a natural harbour. Yes, it’s a delta, like the Nile or the Mississippi (in miniature !). Deltas need big rivers carrying lots of debris, and sure enough the Ness drains a vast area of the west Highlands. Hang on though, the Ness is also one of the shortest big rivers anywhere – a mere 8 miles long. All the debris carried down from the mountains gets trapped in Loch Ness, which is an immensely deep garbage can.
Come to that, no other Scottish rivers have deltas projecting into the sea, and how many other British cities are built on a delta? That’s right, not one, because sea level has yo-yo’d up and down too much for them to grow. Aberdeen – the Dee and Don just end at the coast; Glasgow and Dundee - lining the shore of estuary or firth. Leith docks stick out, but they are on an artificial ‘delta’ reclaimed from the mudflats of the Forth.
So something very unusual has clearly happened here, but what ever could have turned the River Ness into a raging maelstrom, capable of carrying millions of tons of sand and shingle out into the Firth? The answer, incredibly, lies up a well-hidden side valley 60 miles away – at the other end of the Great Glen. And the story of this catastrophic deluge was pieced together by one of Scotland’s greatest living geographers, Brian Sissons, back in the 1970’s.
Glen Roy is a long, winding side valley near Spean Bridge, notable only for one thing – its Parallel Roads. These are the shorelines of a lake which formed in the last ice age just over 10,000 years ago. Glaciers from the corries of Ben Nevis spread out and blocked the mouth of Glen Roy, whose surrounding hills were too low to have glaciers of their own. There are three Parallel Roads, marking stages in the drainage of the lake as low points around it became free of ice. But even at its lowest, the lake was 6 miles long, and held as much water as one of the bigger hydro dams in the Highlands. Imagine pulling the plug on Loch Mullardoch, or Loch Cluanie.
And that’s what happened near Spean Bridge. The ice dam thawed and weakened until the water was able to escape not round it but beneath it, all in one go – carving gorges down into the Great Glen at Loch Lochy. But the way south to Loch Linnhe was still blocked, so the flood water had to turn north past Fort Augustus into Loch Ness. Now all was calm for a short while, as the loch’s vast capacity buffered the shock influx. But steadily, the water level in Loch Ness began to rise, and something like a tidal wave travelled its length. Going past Urquhart Castle, it would have been imperceptible, just like a tsunami out in the deep ocean – Nessie probably didn’t feel a thing.
At Dores, Loch Ness starts to get shallower – and the tidal wave would have grown bigger and bolder until it overran the loch foot and swept on down the valley of the River Ness. Now this valley was choked with masses of sand and stones left by earlier glaciers, easily picked up by the mega-spate. And the valley narrows between Tomnahurich and the Castle, helping to funnel the great flood and spew its debris well out into the firth. It was all over within a day or so.
Before this catastrophe, the Inner Moray Firth (or much better, on the old maps, the “Inverness Firth”) continued uninterrupted into the Beauly Firth – Academy Street would have been a seafront promenade! Now the firth was almost cut in two, and only the flow of the Beauly River and the tidal currents prevented a land bridge joining North and South Kessock.
So what has all this to do with the growth of Inverness into the Hub of the Highlands? Well, early days, the River Ness was easy to bridge at the neck of its delta, and its mouth offered a sheltered harbour with ideal banks for quaysides – and a short ferry crossing to the Black Isle and further north. Then the railway came, and took full advantage of the ample flat land for goods yards and carriage sidings. And of course Longman Industrial Estate now occupies most of the broad, well-drained gravel spread – where would Inverness be if the hills just fell straight into the sea, as they do on the Black Isle?
Back in the seventies, with the Highlands beginning to revive on the back of oil and aluminium, plans were hatched for a fast road to the north. At first it was to go the long way round by Beauly. Then it was decided to take a short cut via Tore – and build a bridge at Kessock. This would have been ruled out as far too expensive if it had had to span the whole firth, like the Tay Bridge. Luckily the Great Flood delta reaches so far out that the bridge is only a short hop, more like Friarton over the Tay at Perth. Indeed it was the boreholes for the bridge that proved this benign catastrophe had happened.
Geoscientists call this kind of flood a jökulhlaup, which is Icelandic for ‘glacier burst’ – there they happen when a volcano erupts under an icecap! There have been other jökulhlaups in the Highlands, but this is the largest recorded freshwater flood Scotland has ever known. Elsewhere in Britain, the Severn Gorge was cut by a glacial lake overflowing, while exciting evidence is emerging for a flood of world scale in the English Channel, when the Thames-Rhine lake breached the Straits of Dover.
Remarkably, you won’t find anything about the Great Inverness Flood in the City Museum, or the Library, or at the Kessock Visitor Centre which overlooks the delta.
David Jarman studies Scotland’s mountain landscapes, and penned this at his Black Isle base. He has a choice of fascinating slide shows for clubs and groups interested in how our mountains have been shaped.
© David Jarman 2004
