So you come to Ilkley, but then look up at the crags above the town, and sigh, You may feel that EarthCaches are just for the hill walking fraternity, and those who can get to remote places, but do not worry there is geology to see in the town.
The Grove in Ilkey is a busy highway, but if you take your time to look about there some geological processes going on. This EarthCache takes you to the public front of Christchurch one of the places of worship in Ilkley. We are interested in the western end of the building and namely the 6 carved faces.
The church is built of sandstone, a sedimenatry rock, though there are enough EarthCaches which look at sandstone and sedimentation. We are here to look at erosion.
Erosion can be caused by a number of factors:
Abrasion - this is where the rock surface is scraped by other rocks and particles carried in water or wind. Imagine a washing machine full of rocks, as it spins the rocks come into contact with the side of the drum and bang and scrape against it. In the case of a washing machine, this would eventually damage the drum, in the case of rock, it causes a circular feature, which gradually over time gets bigger. Stones which have angular features, gradually become round pebbles due to the abrasion of them coming into contact with other stones.
Corrosion - where rocks are broken down by chemicals and/or processes acting on them such as acid contact, heating, or rusting. This type of erosion can be seen in buildings, where sharp features become blunted and curved, as the corrosive action affects the stone. Flaking of rock can also take place.
Hydraulic Action - this is where the action of water itself erodes the rock over time. In the case of a coastline which consists of sand or clay this causes the coastline to gradually retreat.
Freeze-thaw - this is where water freezes in the cracks of the rock, expands and contracts with changing temperatures and eventually the rock erodes.
So lets look at the faces, as I said there are six of them them that we are interested in.
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) Looking at the faces, can you see any evidence of erosion? Please describe your rationale.
(2) Out of all the six faces, which ones are more eroded than the others?
(3) What process of erosion has taken place here?