The Lost Valley EarthCache
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Most people will think of Glencoe and think of the dramatic mountain ranges and deep valleys. The Lost, or Hidden Valley (Coire Gabhail) is one of the more secret and less visited valleys as through the years accessibility has played a part in keeping people away. It's like visiting somewhere out of an Enid Blyton novel. This earthcache will take you into this hidden valley, but beware, the trek will not be for the faint hearted.
Picture, if you will, an ancient mountain range. The peaks are as high as the present day Himalaya, and they extend for over 5,000 kilometres across a vast continent. This is the original Caledonian range. Around 465 million years ago everything changed when three major continents collided in a massive violent movement. The Atlantic Ocean opened and this formed Caledonia, which is of course the latin name for Scotland. The eroded remains of the ancient mountain range are now found in eastern North America, Greenland, Ireland, Scotland Norway and Spitsbergen.
However, the unique features of the Glencoe region are the result of something much more special. Around 420 million years ago, a supervolcano erupted in Glencoe. To be a super volcano, the eruption must eject a volume of magma greater than 1,000 km3 (240 cu mi) - this is thousands of times larger than most historic volcanic eruptions. Supervolcanos have not been common in the United Kingdom. Indeed, only Glencoe here in the Highlands and the Scarfell region of the Lake District can lay claim to such dramatic origins, and it goes without saying that these volcanos died out many years ago.
The result for Glencoe was particularly dramatic, as many consider it to be the best visual example of Cauldron subidence. This essentially is the collapse of a volcanic crater after a large magma chamber has released it's contents. It is marked by a ring fracture, or ring dyke, and you will need to find out what that is as part of your research for claiming this earthcache.
Therefore, when you are walking around Glencoe, you may in fact be walking in what once were underground chambers filled with burning hot magma. Hard to imagine today! In fact the Glencoe volcano produced five major eruptions during it's lifetime; each time the magma was released, a huge void remained. The unsupported rocks above collapsed into the chamber forming a crater, or 'caldera'.
The story doesn't quite end there as much can change in 400 odd million years. In much more recent times, just 10,000 years ago, we experienced the last ice age and the process of glaciation once more shaped the landscape we see today. During the ice age temperatures plummited and large expanses of ice formed, particularly at higher levels, because ice was forming faster than it was melting. Eventually when this ice started to melt the expanses, or glaciers, would move downwards and their size and weight could cause great change to the landscape. Glaciers erode the terrain largely using two methods - abrasion and plucking. You will need to provide a brief description of how each method might have altered the land around Glencoe.
So, this brings us to where you are standing now, the heart of the Hidden Valley. This valley is a large, U-shaped valley but unusually it does not directly connect to the main glen of Glencoe - the valley bottom is completely flat and at the exit of the valley we see a large drop, perhaps 250 metres, before you reach the main valley below. In the past the locals would hide themselves and their livestock in this valley because the steep approach would not suggest to raiders that any such valley would be hidden at the top. Even today, a stiff climb is required to get into it. The bottom of the valley appears like an ancient river bed, but the valley is silent. While there is a river flowing down from the valley, it comes from underground. So what is going on?
This is where you come in. Anyone who takes the time to visit Coire Gabhail, this wonderful hidden valley, will want to take the time to walk around and take in the uniqueness of this dramatic location. While you are there you will need to try and answer the question below. Earthcaches are all about you learning something about the rocks and geology so I hope you will take the time to look more closely at this valley.
Helpful Information?
This 'textbook' information may be of help answering the questions.
- The hills of Glencoe are composed of a suite of different volcanic rocks, in particular pale red rhyolites; silica-rich lavas and ‘welded’ ash deposits and andesites; grey in colour, containing less silica than rhyolite and often spotted with conspicuous cream-white crystals. These two distinct rock types are clearly seen from the road in the Glen looking up to Aonach Dubh. The lower vegetated slopes are composed of andesite while the craggy upper slopes are rhyolite.
- Glacial drift is a general term for the coarsely graded and extremely heterogeneous sediments of glacial origin. Glacial till is that part of glacial drift which was deposited directly by the glacier. Its content may vary from clays to mixtures of clay, sand, gravel and boulders. This material is mostly derived from the subglacial erosion and entrainment by the moving ice of the glaciers of previously available unconsolidated sediments. Bedrock can also be eroded through the action of glacial plucking and abrasion and the resulting clasts of various sizes will be incorporated to the glacier's bed. Eventually, the sedimentary assemblage forming this bed will be abandoned some distance down-ice from its various sources. This is the process of glacial till deposition.
Researching questions 2 and 3 before you go may help you when you are on site.
Questions to Answer
To claim this earthcache, you must answer the following questions and email them to me. Do not post your answers in your log but please do provide a log that gives some thoughts on what you think about the dramatic nature of the Hidden Valley.
I have given you the history of this area and now you must be the geologist and try to determine exactly what you are seeing in the valley based on the information I have provided, and any information you choose to research before you visit the site.
1) The main challenge for claiming this earthcache is to determine the origins of the Hidden Valley. I have explained about the Glencoe volcano and also about the glacial formations. Now you have arrived in the Hidden Valley you must look for clues to see whether you believe this mountain valley was indeed part of the magma chamber - maybe the glacier deepened the main Glencoe valley creating the drop you see today. Or perhaps this valley was completely caused by a glacier and is newer than the main Glencoe Valley. I have searched the web and you will not find the answer through research, nor should you try. When you are in the Hidden Valley you need to look at the rocks, both from a distance and from afar.
- Can you see volcanic rock, if so, where? What type? Any ring fractures?
- Can you see glacial evidence - any sediments, or evidence perhaps of plucking or abrasion?
- Examine the river, the shape of the valley and take note of the exit of the valley and the drop.
What do you think happened here? How do you think this valley was formed? Is it part of the cauldron, is it a glacial valley, or a combination of both?
This answer should be emailed, and you must give some reasoning/evidence about how you reached your conclusion.
Photographs are welcomed showing rocks you believe show 'evidence'. However, you must not give away your final conclusion in your log.
2) What is a cauldron ring fracture, or ring dyke, and why are they formed? You will need to research the answer and email it to me.
3) Can you explain the difference between glacial abrasion and plucking? You will need to research the answer and email it to me.
4) You are in the midst of the Three Sisters, the world famous mountain range. Which sister is west and which is south? Look for the highest point you are able to actually see at GZ and estimate how much higher it is from where you are stood now. This question is optional.
5) Please provide a photograph of yourself or GPSr in or approaching the Hidden Valley. This is optional under geoaching rules but I would like to see photographs and it provides solid evidence you were there if you answers are lacking, making less chance of your log being deleted as I do need evidence that you were indeed there.
Research for this listing has been provided by the National Trust for Scotland, the BBC Science, Lochaber Goepark and other leading geological websites. Many thanks to the National Trust for Scotland who have kindly allowed this earthcache to be placed on their land. The National Trust for Scotland has a visitor centre not far down the road towards Glencoe, and you may also find their extension displays will also help answer the questions for this earthcache.
A final note. The Hidden Valley is not an easy place to reach. The approach is steep, rocky and you may need to wade a shallow river where no bridge has been provided, depending on the route you choose. You should only attempt to reach the Hidden Valley wearing proper boots and you should be prepared for changing weather and the cold. The NTS would not recommend the walk for inexperienced walkers and no easy access has been provided with this in mind. The difficult access is a part of the magic of Coire Gabhail but you must consider this before you attempt the hike. This is part of the NTS Glencoe protected region so please show every respect to the countryside. Many thanks to the National Trust for Scotland for kindly granting permission for this earthcache.
Update: I can see from visitor photographs the NTS have now improved access with a new bridge, some stairs and a roped barrier so it should be a little easier to reach GZ now, which is almost a shame but the original d/t will be retained. I would imagine it will still be challenging to reach the valley but not quite a difficult as back in the day.
Additional Hints
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Treasures
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