Dr J,
It is good to be correct and precise, and I agree that it was a chalk mine collapse, and the definition of a "sink hole" would originally have related to an entirely natural phenomenon.
However the term "sink hole" has been used, incorrectly, for many years, and as such may have become a permanent part of the vocabulary of mine collapses. That, like it or not (and I usually don't) is how language evolves, and, sadly, becomes less precise in many cases. So I think we are stuck with it as far as the press are concerned. But I will try to do better next time.
Meanwhile, we have an example from the past.
http://maps.nls.uk/geo/explore/#zoom=17&lat=56.1273&lon=-3.7749&layers=168 We have "Tibby Ramsay's Sink" (note that there is a gap in the row of council houses, but not quite as big as the original sink hole! Don't buy one!) and "Highlandman's Sink". Both are filled in, and appear as rough ground nowadays, but for many years they were open and called "sinks" by the Ordnance Survey. Now they are in an area of extensive shallow coal mining, which may be assumed to be the cause, but I am now wondering if they are in fact natural sink holes, limestone strata certainly being present.
But across the river in Bo'ness, there were phenomena called "sits", when the strata above a mine working gave way, and "sat down", as in Hemel and St. Albans.
X. Two alarming subsidences have occurred in Bo'ness during the last half-century. They have been described by Mr. Cadell as follows :- "One Sunday evening about thirty years ago, as a local preacher was addressing a meeting on the subject of the fall of the Tower of Siloam in the Old Town Hall below the Clock Tower, and close to the harbour, the congregation were startled by an uncomfortable feeling as if the floor of the building was subsiding beneath them. No active calamity happened, although a terrible danger was very near, and a kind Providence rewarded the faith of the worshippers and permitted them quietly to leave the building after the close of the service. Next day investigations showed that a huge hole 60 feet deep had formed just under the floor, owing to the giving way of the roof of the Wester Main Waste. In a short time the tower began to sink, so as to necessitate its demolition by the authorities. A small shaft was subsequently sunk to ascertain the nature of the cavity, and many had an opportunity of going down and wandering through the old workings about 50 feet below the surface. The seam was about 10 feet thick, and the old miners had worked it in large square pillars, with beautifully dressed faces and an excellent roof. The surface, however, was so near that the thin roof at places had fallen in, and one of the 'sits' had taken place right under the Town Hall. This hole was solidly packed with stone when the Clock Tower was rebuilt. http://www.scottishmining.co.uk/479.html So less than 10 miles from "Tibby Ramsay's Sink", a mine collapse was called a "sit". Most curious....
Unfortunately these features were too transitory to make it into the OS maps, so we can't tell what they would have been called.