Sonar survey reveals the Loch Lomond canyon

SHEER cliffs plunge down hundreds of feet to the bottom of a deep canyon. Jagged hills of hard rock rear up as though from a lunar landscape.

But this is much closer to home for everyone living in Scotland. This is the bonnie, bonnie bed of Loch Lomond.

The images have been produced by a sonar survey carried out by the Edinburgh-based British Geological Survey (BGS). Multi-beam sonar equipment aboard a solar-powered boat produced this fish's eye view from the bottom of the famous loch's narrow north end.

This is how Britain's largest lake by surface area would look if the water was taken out. The depths at the northern end of the 24-mile-long loch have been confirmed as reaching 190 metres, deeper than the North Sea and enough to cover the Glasgow Science Centre tower.

Loch Lomond was created about 10,000 years ago when glaciers swept south during the last Ice Age. The Loch Lomond glacier gouged a deep canyon between surrounding hard-rock mountains and then spread out as it reached its southern extremity where water depths are around a shallower 20 metres.

The first detailed survey was carried out by a team from the Admiralty led by Captain HC Otter who made measurements by dropping a lead weight and line from a rowing boat.

Now Otter's chart will be replaced by the new BGS maps, which are the most detailed images ever produced of the loch bottom. Visitors to the Loch Lomond and the Trossachs National Park will also be able to take 3D loch fly-throughs.

Alan Stevenson, team leader for the BGS's marine geological mapping service, said: "The challenge was to produce a detailed map of the loch floor. At some points it is 190 metres deep at the north end and you don't find that in the open Atlantic until you get out beyond St Kilda."

The maps are to be printed and sold to the 5,500 registered owners on the loch. "What we found is useful from a geological point of view but also for navigation from a safety point of view. The park was happy to allow us do it because Loch Lomond hasn't been properly surveyed since 1861."

Graeme Archibald, the ranger team leader on Loch Lomond, said he was "blown away" by the images. "I was amazed by the steepness of the sides of the loch. It goes down like the Grand Canyon. I have been working on the loch since 1995 but it was only when I saw the BGS maps that I got a real feel for what is underneath the surface.

"We will produce a new chart based on this data in conjunction with BGS and the UK Hydrographic Office, and it will make the loch safer to use for everyone."

Fiona Logan, chief executive of the National Park Authority, said: "It's amazing to think how times have changed since Captain Otter painstakingly carried out his survey using a rowing boat and a lead and line. Using the very latest technology, we can now take a trip navigating our way along past the nooks and crevices and underwater features of the loch using 3D imagery."