Period: Pre-history
The ponds at Spa Ponds are fed by underground springs, including the one which bubbles up on the Western side of Pond 1 (see video above). In living memory people used to even drink from a spring at the site, although that is no longer possible. But why do springs issue at this site? Well, researching that as part of the Spa Ponds Heritage Project took us on quite a journey…a journey all the way back to the ice age…
The lay of the land
While wandering around Spa Ponds you can see how at times it appears to be in a sort of valley, with the land to the east and west often steeply higher. I’ve tried photographing this effect, but it doesn’t capture the awesome sense of scale you feel when you get a good vantage point standing on the central Western edge of the site looking towards the Forestry England land at Garibaldi Planation. If you looked at this on a map that represents changes in elevation (such as the graphics above) you would see that the Spa Ponds site lies in a network of such valleys that form a dendritic (tree-like) pattern in the landscape. This dendritic pattern, my dear Watson, could be a big clue to the site’s origin story.
The Spa Ponds area would have been completely covered by ice during the Anglian Ice Age (which started about 478,000 years ago and ended about 424,000 years ago). However, this area would have been on the edge of the ice sheets during the Devensian Ice Age (around 27,000 years ago). The valley that includes Spa Ponds could have been formed in the interglacial (warm) period between the Anglian and Devensian Ice Ages. This is the likely cause of the dendritic (tree-like) pattern of the landscape, which results in the Spa Ponds site being so much lower than the surrounding landscape.
Why clay may be key
In terms of the springs themselves, we believe that these exist because water is trapped between two layers of Marl clay and, due to its low position in the landscape, Spa Ponds is a place where this trapped water can escape. There are different layers of rock that underlie our part of the Maun valley. The Bunter Sandstone (also known as ‘Nottingham Castle Sandstone’) is youngest and nearer the surface, whereas Lower Mottled Sandstone (also known as ‘Lenton Sandstone’) is older and lower down. It is also softer and more easily eroded. ‘Marl’ which is clay rock rich in lime. Importantly, Marl does not allow water to pass through. This means that any water in the sandstone that is between two layers of Marl will be trapped unless it finds a way out. While there is another spring at a nearby farm, it is possible that there would once have been more springs before they were ‘stopped up’ as part of the process of creating the Duke of Portland’s Water Meadows.
If you’re interested in reading more about this, check out our account of the Reading the Landscape Workshop for the Spa Ponds Heritage Project which was delivered by Stephen Walker.
Next: Domesday (1066-1102)