If it is wet, this EarthCache location will be very slippy, with great potential for you slipping, in this case leave it for another day. Also ensure all pockets are zipped up, and items like car keys, mobile phones are secure. If you drop them here, you are unlikely to get them back.
So, here we are on Middle Scar, with great views across to Ingleborough and south to Penyghent. It is a great place on a warm day, to just sit.
We are atop a limestone outcrop known as Middle Scar. Limestone is a sedimentary rock, this means that it was originally laid down as sediment, and then over time lithified into a rock. There are many types of sedimentary rock, apart from limestone. Other examples are siltstone and sandstones, in their case sediment was silt and sand. In the case of limestone, it originates as lime mud, and / or the accumulation of the shells of dead sea creatures.
Over time, this sediment was overlaid by others, and lithification occured which eventually resulted in the limestone. However, that is not the end of the story, during the icecage, glaciers scrapped away the overlying geology, leaving a bare limestone pavement. Over time, this limestone pavement started to erode, as weathering from ice , snow and rain exploited small cracks and fissures forming what we see today.
Water falling as rain, together with carbon dioxide, formed a weak acid, which then eroded the limestone. We are here to look at a Karren feature known as Horton Type Channels.
What is a karren?
Karren are surface geological features, created by the dissolution of limestone, by weathering and erosion.
Originally, Middle Scar was exposed by the last ice age, as the glacier which covered the Ribblehead area, scoured the land clear, and when it retreated it left a barren expanse of limestone pavement, basically a bare expanse of rock. Over time, small cracks developed, which were exploited by rain and surface water, and erosion occured, and patterns and features known as karren occured. On the surface of limestone pavements, linear grooves which are also named flutes, can develop. These are the result of erosion of the limestone by water over a long time.
So, what are Horton Type Channels?
Horton Type Channels refers to a collection of channels known as rillenkarren. Rillenkarren are narrow channels also known as solution flutes, that tend to run parallel to each other. They are seperated by small ridges.
As erosion occurs, so the channel widens and deepens. It always occurs at the level of the water table in the limestone. Where there is greater concentration of water, so there is greater saturation of the rock and erosion. Eventually a flow of water can occur as the channel widen. This flow of water may concentrate in places, with greater turbulence (flow) causing greater erosion. As this happens so it starts to erode where this happens.
Over time, as the limestone is eroded, rillenkarren can merge with each other, and a complex formation can occur. Imagine a complex city road network with roads merging into each other. Horton Type Channel, is the name for a complex collection of rillenkarren, which takes the form lots of branches like a tree. As the channels develop, they can deepen in places, especially where they have deepened enough to form a sloping channel, and thus water velocity increases, thus further increasing erosion, and the complexity of the Horton Type Channels.
This being an EarthCache, in order to log it, I ask that you answer some questions. Please send them to me, and do not include them in your log. You can send them to me by using the message facility or email, both of which can be found by looking at my profile.
1. As you look at the Horton Type Channels in this location, please describe where you feel that water velocity will be at its greatest, and explain why.
2. Please explain how the orientation of the limestone outcrop here, would contribute to the formation of the Horton Type Channels.
3. Please have your photograph taken, or that of your device pointing towards Pen y ghent.