courtesy of the BBC science and environment webpage. One of those ideas that is so obvious that it doesn't occur to you until someone points it out. Examine coastal erosion by comparing old works of art with modern pics. Hereabouts we have the fantastic work late 19th/early 20th century photographs of Frank Meadow Sutcliffe, prints available from the Sutcliffe Gallery in Whitby.
The Sutcliffe pics of Runswick Bay are here. This is also Runswick and one of my favourite Sutcliffes, filed under 'children'. A child launching a model sailing boat into the calm water at low tide.