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Scientists have measured the way Loch Ness tilts back and forth as the
whole of Scotland bends with the passing of the tides.

It is a tiny signal seen in the way the waters at the ends of the
35km-long lake rise and fall.

When combined with the direct tug from the gravity of the Moon and
Sun, the loch surface goes up and down by just 1.5mm.

The study is reported in the Journal of Geophysical Research.

"If you were on a boat in the middle of the loch, you certainly
wouldn't notice it," said Philip Woodworth from the UK National
Oceanography Centre (NOC), Liverpool, "but a tide like this has never
been observed in a western European lake before."

Prof Woodworth, David Pugh and Machiel Bos say their precision
measurement technique could be used in other lakes around the world to
understand better how the Earth's crust deforms as a result of ocean
movements - rather like a carpenter will use a spirit level to gauge
how a length of wood deviates from the horizontal.

"I have described Loch Ness as the largest spirit level in the world,"
David Pugh, who is a visiting professor at NOC, told BBC News.

None of us can feel it, but Britain rises and falls by centimetres
every 12 hours and 25 minutes as a great bulge of ocean water washes
around the country.

The pencil-shaped Loch Ness is the largest UK lake by volume, and
although inland, is close enough to the North Sea to be influenced by
this loading effect. 

The team placed pressure sensors a few metres under the lake surface
at six locations, from Fort Augustus in the far southwest to Aldourie
in the far northeast. They then monitored the change in the height of
the overlying water during the course of 201 days.

What the scientists saw was a clear spike in the data twice a day -
the result of the gravitational pull of the Moon and Sun. But they
could also tease out a second signal stemming from the way water rises
and falls as a result of the tilting of the land. And, in fact, the
latter effect sits on top of the first and is responsible for most of
the amplitude change.

The team says the measurement was made to an accuracy of just 0.1 mm
over the loch's 35 km length. 

"We had to extract the tidal signal and get rid of all the noise. This
involved very high precision," explained David Pugh.

"For example, the loch surface itself goes up and down every day by
four centimetres just due to the pump storage scheme for hydroelectric
generation, and we have to pull out a very small signal within that. 

"The holy grail would be to learn from the effects of the tides
something about the Earth's crust. So the more precise we can get, the
more we may learn about the crust." 

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter

http://www.bbc.co.uk/news/science-environment-16394421


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