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Healey Dell is a local nature reserve located to the north of Rochdale. The River Spodden runs through it. The River Spodden rises on the moors around Whitworth, it joins the River Roch further south.
Healey Dell is a place of peace, though one which shows the power of nature, particuarly the effects of erosion.
There is a footpath then runs along the valley, and from there it is possible to experience the wonder of the dell, but there is a hidden wonder.
This earthcache allows you to explore a couple of aspects of the geological history of Healey Dell.
First the co-ordinates take you down the steps to the Fairies Cave. Before descending you come across a notice board about the Fairies Cave. Go down and you will enter the bowels of the River Spodden, or to be more specific witness the power of the Spodden in this narrow sandstone gorge known as the Thrutch. After heavy rain, the river is at its most impressive. The viewing platform, gives that Niagra feel, you are right up against the walls of the gorge and close to the rushing waters.
The rock that you see is sandstone, that has been formed during the Carboniferous period.
To be more specific the rock is known as Rough Rock, or First Grit. It was formed during the Yeadonian sub-stage of the Namurian stage of the Carboniferous period, which lasted from 326 to 313 million years ago.
During the Namurian period, a succession of sandstones and mudstones were deposited in a shallow sea between high mountains, when the area that is now Britain lay on a continent called Gondwana. Rivers ran down from the mountains, carrying sands and muds which were deposited in estuaries or deltas.
Duirng the ice age, during which there had been a glacial lake bounded by a glacial moraine, a large quantity of meltwater from this occured, and since then the valley bottom has been eroded by the action of the River Spodden.
Here are the Thrutch, the river has over time eroded the sandstone to make the narrow gorge that we see today.
Erosion takes place through two methods-
lateral and vertical erosion which take place in a river. Lateral erosion refers to widening of the river channel through erosion of the sides of the river. Vertical erosion is deepening of the river channel through erosion of the river bed.
Whether it is lateral or vertical erosion, they are four ways a river is eroded.
1. Solution/corrosion: The river water acts as a solvent and dissolves soluble minerals such as limestone. The presence of carbon dioxide would help to dissolve limestone (calcium carbonate) faster due to the chemical reaction between them.
2. Attrition: Materials carried away by the river become smaller, rounder and smoother after colliding with one another during transportation.
3. Hydraulic action: The power of fast-moving water breaks and loosens materials after hitting the river banks and bed. As the water enters the lines of weakness in the rocks, it exerts a great force to break the rocks into fragments.
4. Abrasion/corrasion: The load of a river grinds against the sides and bed of the river channel, removing materials, thus widening and deepening the channel.
Here at the Thrutch, attrition, hydraulic action and brasion/corrasion all have played their part in the process of vertical erosion. An important date in the history of the Fairies Cave, is the great flood of the 4th July 1838. A large outburst of wet weather fell on the fells above the valley, which led to the River Spodden raising by 4 metres, and caused subsequent destruction downstream, and the hydraulic action caused the gorge that we see toady to be in its current form. Before that the gorge had a different appearance.
From the viewing platform you can see curving on the walls of the gorge, this is where the river has eroded the stone.
Whe visiting this earthcache please be careful. There are a number of steps to go down and up, and you are close to the water, so please be careful.
At this location , please answer the following questions and contact Hillgorilla with the answers:
(1). How many steps are there down to the viewing platform.
(2) How wide is the gorge (please just estimate - there is no need to cross the barrier)?
(3) How tall do you think the gorge is?
(4) Can you see any evidence of erosion by the river, what does it look like?
(5) As an option, a picture of
(i) You or your GPS at the cache site.
(ii) Pictures of the gorge.
(iii) Pictures of evidence of erosion.
After leaving the Fairies Cave, go back up the steps to the footpath, walk in a southerly direction to Waypoint 1.
Here you can see walls of Rough Rock, which have been quarried back at a point in the past. The reason for this, is that originally there was a a coal seam here, the mine being known as the Upper Foot Mine.
Here you can get up and close to the rough rock.
Please answer the following questions here, and contact Hillgorilla with the answers:
(1) How does the rock feel?
(2) What colour is the rock?
(3) Photographs of yourself or your GPS here would be welcomed - though these are optional.
Thank you to Richard Whittle, Healey Dell Ranger for his assistance with this earthcache and information. Information also gained through reference to Bolton (1890). The Geology of Rossendale, and my son whose school work about geography has increased my knowledge.
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