The formation of the hot springs at Bath Spa, UK

The hot springs that emerge at 46 °C in the centre of Bath Spa, Somerset, are unique in the UK. The four other thermal springs in Britain are also sourced in the Carboniferous Limestone, but they emerge at significantly lower temperatures (20 to 28 °C). Bath is situated in a region of low geothermal gradient (about 20 °C/km depth) in a geological setting that seems an unlikely place for hot springs. Why then are these the only hot springs in Britain, and why are they confined to such a small (20 × 80 m) area? The explanation presented here involves a sequence of geological events involving Triassic dissolution and Pleistocene permafrost that is unique to central Bath.