Slade Brook is an unusual tufa stream and site of biological and geological Site of Special Scientific Interest (SSSI)
This EarthCache involves a steep walk through woodland, possibly very muddy paths and some uneven ground. Please take care while you enjoy this atmospheric and unusual area - and Natural England ask that that the stream and woodland habitat should be preserved by sticking to the public footpaths within the SSSI.
Location and habitat
The site, the basis of which is an active tufa-forming stream, is in the Forest of Dean plateau and Wye Valley Area of Outstanding Natural Beauty. The stream system has a series of tufa dams, plunge pools and connecting stream sections. This results from a combination of physical and chemical processes.
The Slade Brook rises on the Carboniferous Limestone of the Forest of Dean. It flows for two kilometres before joining the River Wye which is also notified as an SSSI. Approximately a kilometre section of the stream includes the main focus of tufa deposition.
What is Tufa?
Tufa is a highly porous, sedimentary rock (limestone) composed of calcium carbonate (Chemical symbol = CaCO3) It is formed by biological and chemical precipitation of Calcite from cold surface or ground waters. ... Fresh tufa often contains remains of trees, branches, leaves, fossil one their formation.
Rainwater (which percolates into sinkholes in the limestone), is enriched with dissolved calcium carbonate. When emerging from springs along the brook, the removal or purging of carbon dioxide causes precipitation of calcium carbonate. The main deposits of the calcium carbonate are at a series of dam-like structures, which are gradually constructed of the tufa deposits. One would expect them to form at steps on the limestone, where the water is going down a natural waterfall. The turbulence encourages the deposition of the tufa - the water coming out of limestone can be above 100% saturation in Calcium Carbonate, so it wants to deposit tufa. As the deposits grow they form larger and larger or wider dam-like structures known as screens.
The process is assisted by vegetation (which includes tree litter such as twigs and branches), algae and mosses. The flow of the stream is slowed down and photosynthesis encourages the removal of the carbon dioxide. The vegetation and debris then become the area for tufa accumulation, also adding to the buildup of the dams.
The Slade Brook site is significant as tufa dams actively forming are relatively rare and this site has approximately sixty. They enable research into the origins of fossil tufa dams as well as modern formations. (some information found with the help of wikipedia)
As this is an EarthCache there is no physical container to find, just a couple of questions to answer, at two different waypoints about a 10 minute walk apart.
At the headline Co-ordinates you should be able to see the stream coming down the slope from the north and under the 'road' you are on.
1. Here you should observe a large Tufa Screen (dam). Please describe how or why you think it has formed. Is it affecting the waterflow and will this affect other dams and formations? The information above should help your answer and please feel free to be as descriptive as possible in your explanation!
To get to the second stage just follow the path down, running parallel to the stream.
2. The screens visible from this waypoint (a very long footbridge) are different in size and structure from the one seen earlier. Why do you think this could be? Thinking about the stream bed and water flow will help you explain your observations.
Finally, whilst at the bridge, please tell me who carried out 'these improvements' (information on one end the bridge itself).
Photos of cachers visiting the site are appreciated, although not required for logging the cache.
Please feel free to log your find, then you can send your answers and descriptions to me via the website message centre or email.
This EarthCache has been given permission by Natural England West Midlands Office