Great Slab on Bowfell: ancient caldera lake

Great Slab on Bowfell was one of my great days out this year. I had been thinking about a post about coordinates on an inclined plane. But then I found out why it is so flat: volcanic ash settling in water in an ancient caldera lake. This time last year I was in a modern caldera. And the evidence as to why it was a freshwater lake is given on http://www.ronaldturnbull.co.uk/pics/geopix/Pages/17.html