Druid's Temple EarthCache

Situated on the Swinton Estate in the middle of a pine forest, the Druid's Temple folly was created by William Danby in the early 1800s to look something like Stonehenge. It features an oval of altars, menhirs, dolmens and sarsens, and several solitary standing stones line an avenue that leads to the temple. It is thought that this labour-intensive work was to relieve some of the unemployment in the area and workers were paid a shilling a day. 

Stone is definately the theme you will see when you visit here so it is an ideal opportunity to present you with an EarthCache and the opportunity to learn something of the rocks you will see all around you.

The rocks here began taking their shape roughly 320 million years ago, when water, grit, and sand washed down from Scotland and Norway to form the land of Yorkshire. During the last glacial period, geological forces got to work and the rocks were shaped into sometimes bizarre shapes as can be seen not so far away at Brimham Rocks, which is the same rock type you find here. As the last of the giant ice age glaciers melted in Nidderdale they created the ripples and waves on the rocks, resulting in sculpted looking forms.

Specifically, it is Upper Brimham Grit that you find around Ilton and quarries here often produced the stone. For the most part, it is a massive, cross-bedded sandstone ideal for being cut into large blocks. It was also a good stone for carving, being used on local churches where you can see some good uses of the stone. Gritstone is made up of the cemented deposits of rounded grains. These range in size between coarse sand to gravel. In some gritstones the grains can be easily rubbed out, while in others a strong cement makes the rock suitable for use as a grinding stone, such as Millstone Grit. Quartz is always the greatest component, but it often contains iron oxides giving it a yellow, brown, or red colour.

In this EarthCache we will be looking at the difference between erosion and weathering and which of the two have affected Druid's Temple and the rocks around it. Erosion involves removal of solid material by a transporting agent. Weathering is the breakdown of rock into fragments at the Earth’s surface. The key thing to remember is that no movement is involved in weathering.

Erosion is all about movement - erosion is the process by which soil and rock particles are worn away and moved elsewhere. This transportation or movement is usually caused by either wind, water, ice or gravity. 

Erosion By Wind

Wind erosion is a serious environmental problem in the driest parts of the world, removing soil from farmland and covering whole towns with sand and dust. A strong breeze (wind speed 20 km/h) can easily pick up dry dust and fine sand. The lightest particles are swirled up into the air and carried in suspension for hundreds of kilometres, whilst sand grains bounce along the surface by saltation. Small pebbles can be moved along with the sand, a process called creep. Sand dunes form when wind-blown sand starts to pile up. Sand is eroded from the up-wind side of the dune and deposited on the down-wind side, so the whole dune gradually migrates down-wind. In this country, our peat moorlands have suffered greatly from wind erosion in the summer when they dry out and there is nothing growing in the peat to stop the peat simply being blown away when it has dried out. Most often, wind erosion occurs on flat land in dry or sandy areas. A rock that is exposed to wind over time could be gradually eroded, and the softer the rock is, the more likely this may be to occur.

Erosion By Ice

A glacier is a river of ice formed from compacted snow. Although in the UK we think of them as something long ago in our past, they are still common in the Polar regions (e.g. Antarctica) and in mountain regions like the Alps and Himalayas. Glaciers move slowly down valleys (at speeds up to a few metres per day), but have enormous erosive power. Water at the base of the glacier can enter cracks in the bedrock and re-freezes, causing the rock to break apart. As the glacier continues to move the broken rock gets stuck in the ice and carried away. As the glacier moves downhill, rock fragments embedded in the ice at the base of the glacier scrape and grind against rock beneath the ice leaving distinctive and long lasting marks. Glaciers erode rapidly downward, forming deep, U-shaped valleys. Once this damage has been caused to very hard volcanic rocks such as granite, it remains visible millions of years later leaving gouges or lines in the rocks so we can still clearly see where ice has eroded these stones. However, in softer rocks such as gritstone, on-going erosion over time is likely to mean the rock continues to change shape.

Erosion By Liquid Water

Around the world, moving water picks up and transports millions of tonnes of sediment every day, along rivers, coasts, and even in the deep oceans. Sediment, whether picked up by flowing water or by waves, is moved along in one of four ways: 

- Traction is the rolling or dragging of large grains along a river bed or shore, aided by the push of the smaller grains (below).
- Saltation is the bouncing of sand grains as they are picked up, carried along, and dropped repeatedly by flowing water. 
- Fine particles (silt and clay) are carried in Suspension in the water – they will only settle out if the water is still. 
- Soluble salts are carried in Solution in the water – the sea is obviously salty, but rivers contain dissolved salts, too.

The bed load of a river (pebbles and sand grains) helps to erode the river bed and banks by abrasion, especially when the river is in flood. In a similar way, waves cause cliffs to erode especially during storms. As the pebbles and sand grind away the river bed or sea shore, they also become smaller and more rounded, a process called attrition. As mentioned in the introduction, remember that when the glaciers melted in this region they created a large amount of flowing water so the effects mentioned above may have occured quite intensly over that period creating significant water erosion that then stopped once it had melted.

Erosion By Gravity

This downward pull of gravity can cause materials to move from areas of higher elevation to areas of lower elevation. The force of gravity can cause rocks and glaciers to move down mountain slopes, and also cause rivers to flow toward the oceans. Landslides are the sudden mass erosion of rocks down a hill, soil creep is a much slower erosion but again, the downward movement of material.

Weathering does not involve any movement - weathering is the breakdown of rocks at the Earth's surface, by the action of rainwater, extremes of temperature, and biological activity. It does not involve the removal of rock material.

Physical (Mechanical) Weathering

Physical or mechanical weathering takes place when rocks are broken down without any change in the chemical nature of the rocks. The rocks are essentially torn apart by physical force.

The most common type of physical weathering is the constant freezing, and thawing of water, known as freeze thaw. In liquid form, water is able to penetrate the many holes, joints, and fissures within a rock. As the temperature drops, this water freezes. As water freezes, it expands, becoming about 10% larger than it was in liquid form. The result is that the holes and cracks in rocks are pushed outward. Even the strongest rocks are no match for this force. As the water thaws, it is then able to penetrate further into the widened space, where it later freezes yet again. The expansion of holes and cracks is very slow. Month after month, year after year, water freezes and thaws over and over, creating larger and larger holes and cracks in the rocks.

Another important type of mechanical weathering is salt wedging. As water enters the holes and cracks in the surface of rocks, it often carries salt with it. As the water later evaporates, the salt is left behind. Over time, these salt deposits build up, creating pressure that can cause rocks to split and weaken. Temperature changes also effect mechanical weathering. As temperatures heat up, the rocks themselves expand somewhat. As the temperatures cool down, rocks contract slightly. The effect can be the weakening of the rock itself.

Chemical Weathering

Chemical weathering is caused by rain water reacting with the mineral grains in rocks to form new minerals (clays) and soluble salts. These reactions occur particularly when the water is slightly acidic. These chemical processes need water, and occur more rapidly at higher temperature, so warm, damp climates are best. Chemical weathering (especially hydrolysis and oxidation) is the first stage in the production of soils.

There are different types of chemical weathering, the most important are:

- Solution - removal of rock in solution by acidic rainwater. In particular, limestone is weathered by rainwater containing dissolved CO2, (this process is sometimes called carbonation).

- Hydrolysis - the breakdown of rock by acidic water to produce clay and soluble salts. 

- Oxidation - the breakdown of rock by oxygen and water, often giving iron-rich rocks a rusty-coloured weathered surface.

Biological Weathering

Living organisms contribute to the weathering process in many ways. Trees put down roots through joints or cracks in the rock in order to find moisture. As the tree grows, the roots gradually prize the rock apart. Many animals, such as Piddock shells, bore into rocks for protection either by scraping away the grains or secreting acid to dissolve the rock. Even the tiniest bacteria, algae and lichens produce chemicals that help break down the rock on which they live, so they can get the nutrients they need.

As this is an EarthCache there is nothing hidden here to find, please don't search. Instead, you must answer a number of questions in order to log your find. You are not expected to have any previous knowledge of geology or rocks, so please do give it a try. All the information you need to answer the questions is found by reading the information above and I only ask you make an attempt at answering the questions. If you don't send in any answers at all, your log may be deleted.

Please note, this is an observational earthcache. This means you should read the relevant information and then look for actual evidence on the rocks (for example shapes, cracks or growth) that match with the descriptions. No hypothetical guesses are required so please only base your answers on what you see - this should make it easier but please take a little time to look around.

Question 1)
Firstly, take a look at the natural rocks that have not been changed by man and are found in various places outside the stone circle. There is an excellent example sat on the elevated area on the opposite side of the stone circle to the path. Another interesting one is a rock sat on another rock in the woods on the opposite side of the path from the stone circle. There are many others dotted about.  Here we are going to look at the effects of erosion. Please look closely at some of the natural rocks here and their shapes. What evidence can you see of the rocks being shaped or eroded naturally? Having read the 'erosion' section above, what type of erosion do you think has caused the shapes you have seen (wind, ice or water) and why do you think that?

Question 2)
Turn your attention to the stones used to build Druid's Temple. Nothing is mentioned in the history of the stone circle as to whether it was built using local stone, so although it is likely, you need to investigate. Compare the texture/colour of a natural stone you looked at in question 1 with the stones used to build Druid's Temple. We know the local stone is Upper Brimham Gritstone (information about this stone is found in the introduction) - do you think the Druid's Temple is built using the same local stone?

Question 3)
Again, look at the stones used to construct Druid's Temple. Man may have cut or shaped these stones, however, the stones will have weathered since Druid's Temple was built. Having read the 'weathering' section above, what types of weathering can you see here (physical, chemical, or biological)? Do you see any erosion in these rocks and how is it different to the weathering?

Question 4)
Now go to waypoint 1 which isn't far away. This is another distinct man made feature. Most of the stones you will have seen are tones of grey but here there is a very different colour visible on some of the rocks here. What colour do you see and what do you think has caused it? The introduction and weathering sections will both help you here.

Question 5)
Finally, at waypoint 1, a number of rocks have been arranged by man here in different ways. To prove you have been here, how many rocks are piled in the middle, and how many are around the outside in a circle?

Optionally...
A photograph of you somewhere in Druid's Temple would be greatly appreciated (although is not mandatory). Please try to avoid giving obvious spoilers and please don't include photos at waypoint 1.