An EarthCache is a special geological location people can visit to learn about a feature of the natural world around them.
This EarthCache concerns the WEATHERING of SANDSTONE.
There is no physical container to find, just information.
Please note that there is no need to go on the bridge or over the road - all the observations can be made from GZ in the car park.
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ECKINGTON BRIDGE is a stone bridge over the River Avon. It is a Grade II* listed buidling and has been scheduled as an ancient monument.
The first bridge at the site was built in 1440, replacing an earlier ferry, but this fell into disrepair and was replaced by the current stone bridge in the 1720s. It is built of red sandstone and has six arches. It is a local landmark and shows many signs of weathering and erosion - please look closely at the bridge and how the sandstone differs across the various parts of the structure.
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Read the information below as it will help you to answer the EarthCache questions.
RED SANDSTONE is a type of rock that forms when grains of sand are compacted together over significant periods of time. Normally this sand is rich is quartz but can also contain other minerals and materials such as calcium carbonate and silica. Sandstone comes in a variety of colors including red, yellow, grey, and brown - red sandstone contains a high proportion of iron oxide (rust).
The formation of this sandstone involves two principal stages. First, a layer or layers of sand accumulates as the result of sedimentation either from water (as in a stream, lake, or sea) or from air (as in a desert). Typically, sedimentation occurs by the sand settling out from suspension; for example, ceasing to be rolled or bounced along the bottom of a body of water or ground surface ( in a desert). Finally, once it has accumulated, the sand eventually becomes sandstone when it is compacted by the pressure of overlying deposits and cemented by the precipitation of minerals within the pore spaces between sand grains. The most common cementing materials are silica and calcium carbonate.
Sandstone has been used for domestic construction and housewares since prehistoric times, and continues to be used. It is relatively soft, making it easy to carve. It has been widely used around the world in constructing temples, homes, and other buildings. It has also been used for artistic purposes to create ornamental fountains and statues.
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Weathering
This describes the breakdown of rock through exposure to the atmosphere. It can happen in three main ways...
1. Chemical Weathering
Rainwater is naturally slightly acidic because carbon dioxide from the air, or other man made pollutants, dissolves in it. Minerals in rocks may react with the rainwater, causing the rock to be weathered. This could take the form of discolouration as well as eventual erosion.
Some types of rock are easily weathered by chemicals. For example, limestone and chalk are made of a mineral called calcium carbonate. When acidic rainwater falls on calcium carbonate, a chemical reaction happens. New soluble substances are formed in the reaction. These are washed away and the rock is weathered.
Chemical weathering can hollow out caves form and make cliffs fall away.
2. Biological Weathering
This can cause the breaking and/or crumbling of the stones by tree roots, plants or animals. Also common is the damage caused by lichens or organisms growing on the surface of rocks. Lichen takes the nutrients it needs from the surface of the limestone. Changes in the composition of the rocks can weaken them.
3. Physical Weathering
Weathering from physical factors can change the shape of the rock, rather than the actual composition. Heat can expand stones, while cold will cause contraction. This process over a period of time will cause the stones to fracture and crack. Rainwater can then also seep into cracks in the rock, and, if frozen, will expand and make these cracks bigger and wider.
Wind can also affect loose grains of stone, causing more damage.
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The information above should give you some new and interesting facts. Use your new found knowledge to answer the following questions to help you to log this EarthCache. The questions relate to how the stone has been affected by weathering over the last few hundred years.
1. Along the top capstones of the bridge the colour is very different to the rest of the stonework. Why do you think this might be?
2. While most of the stones have/had squared edges, the stones around the top of the arches appear weathered. What factors might have caused this obvious weathering?
3. On the nearby circular walk sign, how many gates and stiles does it say there are?
You can send your answers to me via the website message centre, or email, but feel free to log your visit.
Photos of cachers visits to the site are appreciated (please try to avoid giving away any spoilers in your shots!) but not a requirement for logging. I hope you enjoy this EarthCache, and the wharf picnic area!