This is the only thermal spring in Wales. The spring emerges on the eastern bank of the River Taff and has been contained within a brick well structure and building. Access is via Taff’s Well public park; if the well is locked try and locate the park keeper to open it for you. Parking is on Cardiff Road, but there is a small car park on Park Road, downhill, just below the pub.
THIS PICTURE WAS TAKEN BACK IN THE 1930's. YOU CAN JUST SEE THE OUTLINE OF THE BUILDING AS IT IS NOW.
Presumably because of dissolved minerals and the warmth, some 19th century guides claimed medicinal properties of the water, especially for the cure of rheumatism and the waters are said to possess medicinal properties of very high order. The spring reached its height of popularity during the mid to late 1800s, with visitors arriving in the village in large numbers hoping to cure their ailments.
The spring emerges from the southern limb of the South Wales Coalfield. Carboniferous "Millstone Grit" (Marros Group) occurs in the immediate area of the thermal spring, but has little significance, in relation to the spring..
However the limestone is important. It is a rock with many cracks and fissures which allows freer percolation of water both downwards and later upwards as warmed water.
Limestone landscapes show characteristic landforms caused by chemical dissolution, such as karren (crevices and channels, tens of cm wide), and dolines and sinkholes (closed depressions, tens of m in diameter). Streams and rivers sinking underground via swallow holes are also frequent. This is a Karst aquifer characterised by a network of conduits formed by chemical dissolution, allowing for water flow. A karst aquifer may be present even when there are no discernible karst landforms at the land surface, and even when there are no known and accessible caves.
This underlying Carboniferous Limestone can be seen outcropping just south of Taff’s Well. Then underneath the porous limestone aquifer is the less porous and older Devonian Old Red Sandstone. It also outcrops about 2 km southeast, just north of the M4 motorway
The nearby surface geology in the area of the Taff’s Well spring comprises an unknown thickness of river alluvium and river terrace deposits, (mud and pebbles). This has not presented any problems recently, however there was a significant problem in the past. (Q.5 - see noticeboard on site)
Massive earth movements occurred in this area, adding to the fractured nature of the rocks .
Taff’s Well is bound to the south west by the Tongwynlais or Taff's Well Fault, which runs north-south, crossing the River Taff and passing very close to the Taff's Well Thermal Spring. The Taffs Well Fault is a continuation of the Daren-ddu fault which is a major NW-SE trending fault in the Coal Measure rocks of the South Wales Coalfield.
The Tongwynlais Fault is a normal fault and affects both the Carboniferous limestone and underlying Devonian Upper Old Red Sandstone. The fault has a downthrow of 85m to the west. All of this resulted in more fractures , fissures, faults and channels in the rock.
The water is thought to flow largely within the Carboniferous Limestone Group from sources on the north crop of the coalfield.
There is a syncline here, which acts like a "basin". It is a fold of rock layers that slope upward on both sides of a common low point. Synclines form when rocks are compressed by plate-tectonic forces. Cold water is heated geo-thermally before rising to the surface from the lowest levels of this syncline, within the aquifer, (a body of permeable rock which contains or transmit groundwater), but above the less permeable Devonian rocks.
Thermal springs are produced by the emergence of heated water that rises from the Earth's crust. BUT the source of the heat will vary.
For example, in certain parts of the world, several types of rock contain radioactive substances such as uranium. Radioactive decay of these substances releases heat energy, which warms up the rocks. In volcanic areas, the rocks or magma may heat water so that it rises to the surface naturally as hot water and steam.
In this area, there are no volcanic influences, but the rocks deep underground are hot, and cold water percolates down. The water runs through fractures in the rocks and is heated up. And forced up by pressure.
There is a fundamental law of geophysics: The farther you go underground, the hotter it gets and the more intense the pressure.
While it may be a pleasant 24º C five kilometres below the surface, at extreme depths you would encounter extremely high temperatures and pressures so intense that ordinary carbon is transformed into precious diamonds.
Geologists calculate that, for every kilometre you dig beneath the Earth's surface, the temperature rises ±7º C and the pressure increases simultaneously at a rate of about 525 kilograms per square centimetre (kgf/cm²)
There are geothermal hot springs in many locations all over the crust of the earth. Depending how deep the water percolates the some of these springs contain water that is a safe temperature for bathing, others are so hot that immersion can result in injury or death.
THE KEY PRINCIPLE FOR THIS EARTHCACHE, IS THAT IN GENERAL, THE TEMPERATURE OF THE ROCKS WITHIN THE EARTH INCREASES WITH DEPTH.
The rate of temperature increase with depth is known as the geothermal gradient. .
If water percolates deep enough into the crust, it will be heated as it comes into contact with hot rocks. The water in thermal springs, in non-volcanic areas, such as this, is heated in this manner. SEE THE DIAGRAM BELOW.
KEY INFORMATION.
The water which bubbles up from the ground at Bath, just across the Bristol Channel, falls as rain on the nearby Mendip Hills. It percolates down through it's Carboniferous Limestone aquifer to a depth of between 2,700 and 4,300 metres (8,900 and 14,100 ft) where geothermal energy raises the water temperature to between 69 and 96 °C (156 and 205°F). Under pressure, the heated water rises to the surface along fissures and faults in the limestone
References
1. Farr, G. (2014). Taff’s Well/ Ffynnon Taf, The World’s Smallest Spa. [In Press and available for free download]
2. Farr, G & Bottrell, S.H. (2013). Hydrogeology and hydrochemistry of the thermal waters at Taff’s Well. Cave and Karst Science Vol. 40 Issue 1. Free download from the British Cave Research Association.
VISIT THE SITE
Your Task
There are several information boards close to the spring and a free audio description. Research on the internet will generate some different answers, BUT only the data available to you on site will be accepted.
USE THESE BOARDS AND THE TEXT ABOVE TO CONSIDER THE TASKS and then message, or email us your responses. Go ahead and log your find, but PLEASE don't put answers in your log. Upload any photos you want except of the info. boards.
I will you contact ASAP either through the message centre or email.
ANY "FINDS" WITHOUT ACCOMPANYING ANSWERS WILL, REGRETFULLY, BE DELETED
LOGGING TASKS
According to the information boards.
1. How old is the water and how deep has it sunk underground here?
2. At what temperature does it typically emerge here?
3. Using your previous answers as a GUIDE for your response. Can you suggest why the water in Taff's Well emerges at a different temperature to the water in Bath? ( only about 40 miles away, "as the crow flies")
4. From the text above, identify the geological principle which supports your answer
5. DO NOT FORGET TO INCLUDE A NON SPOILER REQUIRED PHOTO OF YOU OR A PERSONAL ITEM,SUCH AS YOUR CACHING NAME.
((Rule Change Updated 10 June, 2019 Geocachers can be asked to provide a photo of themselves or a personal item to prove they visited the site.))
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