Saturday, 27 June 2009

Where We Map

A while ago I had a brief conversation with (((Billy))) about mapping in the UK, where we rarely have exceptional exposure and where a lot of our mapping is carried out by playing a game of dot-to-dot, joining up sections across valleys, using boreholes and logs, and doing the old-fashioned things like measuring the dip and strike of the contacts and extrapolating them along the topography.

My mapping area was the Uldale Fells, in the northern Lake District. In theory, I had an astoundingly good area: a metamorphic aureole around a granite intrusion, the less metamorphosed rocks being Ordovician turbidites, and a bit of subaerial volcanics up in the north of the area, complete with contact metamorphism to greenschist facies.

In practice, I had this to map:

You might just be able to see the exposure in the stream sections...

If I was really lucky, I had exposure like this, at Roughton Gill mines:

The highest point in my mapping area (and indeed the whole of the Uldale Fells) was Knott, at 723m. I don't think that even counts as a hill in the USA, let alone a mountain. Latitude-wise, at about 55°N, the Lake District receives less sunlight than the southwest USA, and that and the sheer amount of rain the Lake District is subjected to each year (why do you think it's called the Lake District?) results in a heavily grass-covered, wet environment, which isn't particularly conducive to the exposure of the bedrock.

So what sort of detail can we get out of this sort of area? Tune in next time to see my maps themselves...

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