Welcome to my 200th hide, and my second earthcache…
From the guidelines of creating an earthcache, “The cache page, including the description and logging tasks, must assume only a basic knowledge of geology.”
I have a basic knowledge of geology, but I am often confused by many earthcaches that seem to assume a much higher proficiency in geology. So, for this one I am taking it down a level. Also, the questions aren’t all at the end, they are dotted throughout, so you can’t skip to the end and answer the questions, you need to read my drivel first and answer the questions as you go.
Once you arrive at the published GZ you will be greeted by an outcrop of granite rock. "Oh no", I hear you say, "Not another earthcache about granite!" Which is fair, but this granite outcrop is very much unlike most other outcrops of granite rock that you are likely to see. To get the tedious stuff out of the way, granite is an igneous rock. Igneous is one of three types of rock. It's the rock that is formed by lava or magma, as distinct from sedimentary rocks that is formed by layering of small particles, usually on the ocean floor and metamorphic rocks that are rocks that arises from other rocks that have been exposed to extreme heat and/or pressure.
Question 1 – What type of rock (sedimentary, igneous or metamorphic) is Elephant Rock and what formed it?
Granite can be made up of lots of different compositions, and I’m not going to bore you by telling you what they all are and what they mean, but for now its safe to assume that granite has in it this thing called Feldspars which are a heavy mineral that make up the majority of the Earth’s continental crust (the continental crust includes all the continents and land masses and also the shallow seas near the land, but not the deep ocean bits). Granite also contains a lot of quartz which is a mineral composed of silicon and oxygen and is the second most abundant mineral in the Earth’s continental crust. This all serves to make granite very common, very hard and very dense (approximately 2.7 ton per cubic metre), and these are the three reasons why granite has been used so frequently through the modern history of man, for everything from kitchen counter tops to gravestones.
Question 2 – Looking at Elephant Rock in front of you, given you know now how many tons per cubic metre that granite weighs, how much do you estimate that all of Elephant rock weighs? (estimates only, doesn't have to be exact).
So, granite is this really hard rock that is formed deep within the Earth's crust from cooling magma and is usually transported to the surface probably via plate techtonics. Plate techtonics is a theory which describes the movement of multiple plates around the earth, causing things like continental drift, earthqakes, mountain ranges and ridges as well as pushing rocks from the bowels of the earth to the surface. You could do another highly interesting earthcache on plate techtonics alone, and many others have, so I won't go into it too much here. But, in the end, the granite boulder ends up usually just beneath the surface, underneath a mantle of soil that is formed from decomposing vegetation, as well as plants and trees. Then, as the vegetation breaks down, the layer of soil above the underlying granite gets thicker and thicker, usually totally covering the boulder.
Usually.
Except, in some places (such as this one), where the cover is removed, most likely through erosion, the underlying granite is left exposed, to form a granite outcrop. There are several more prominent versions of granite outcrops in the area than Elephant Rock. The other outcrops are well worth going for a visit, not just because they are cool granite outcrops, but they also have some pretty amazing caches there as well (see Egg Rock GCPFHB-Eggcellent View by Team Crackers and my absolute favourite Seven Acre Rock GCH199-Prime Real Estate by geofreak).
Question 3 – What type of erosion (rainfall, river, coastal, chemical, wind, glacial or flood) do you think has been the predominant cause of the removal of the soil at this location to expose Elephant Rock?
I said before that there are more prominent versions of granite outcrops in the area, but I have chosen to highlight Elephant rock for two reasons.
- Its much closer to my house and
- There is something quite unique about Elephant Rock and how it appears.
If you touch and feel elephant rock, it doesn’t feel like normal granite. If you stand back and look at it, it doesn’t look like normal granite. This is a very good thing because it means I can't ask you ambiguous questions about what colours you see in the rock or the size of the quartz in the rock. There is an additional process going on here though that is changing the way that Elephant Rock looks and feels.
Question 4 – Describe the texture of Elephant Rock and send through a photo of how Elephant rock appeared when you were there and then explain to me the additional process that you believe is causing this to not feel and look like regular granite.
And that’s about it. You have four logging tasks (questions), don’t forget the photo for the fourth one (it doesn’t have to have you in it, but it can if you are feeling particularly photogenic). You can claim the smilie straight away but make sure you send through your answers to the four logging tasks otherwise I will delete your find. They can be sent via a geocaching message, an email, a text message (if you have my phone number), a Facebook PM, on whatsapp or via smoke signal, I don't care, as long as I get them.
Hope you had fun, and enjoyed this earthcache.