Buckland Beacon EarthCache
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A flat walk from a reasonable parking area (for perhaps 6 cars) with outstanding views. The walk ends at Buckland Beacon (about a mile away from parking area) where you will also see the Ten Commandment Stones engraved into two great flat tablets of stone.
Parking Location:
N 50.32.607
W 003.46.771
Dartmoor National Park Authority
www.dartmoor-npa.gov.uk
Postal Address
Dartmoor National Park Authority
Parke
Bovey Tracey
Newton Abbot
Devon
UK
TQ13 9JQ
Tel +44(0) 1626 832093
Fax +44 (0) 1626 834684
Email: hq@dartmoor-npa.gov.uk
Parking, and an official footpath along the side of a dry stone wall ensures visitors to the area stay to the path and do not cause erosion or damage to the moors.
Dartmoor is well known for its rolling hills, its deep valleys and its proud granite tors.
This particular location is quite remarkable as you will see the massive extent of the Dart Valley fall away beneath your feet while standing on a prominent tor, known as Buckland Beacon.
Contrary to some belief, this is not actually a glaciated valley.
The Dart Valley below the beacon is in fact cutting a gorge not in granite but in mudstones and sandstones which have been baked and hardened by the emplacement of the nearby granite at a temperature of about 800 degrees celcius some 280 million years ago. Buckland Beacon is very close to the contact between the granite and the sedimentary rocks into which it was intruded (deep in the earth’s crust at that time). All round Dartmoor, where the rivers come off the granite onto the baked sedimentary rocks, they form steep gorges – this reflects the fact that the baked rocks are quite resistant and have maintained steep hillside slopes as the rivers have cut down over time. Much of this river activity has taken place in the last 2.5 million years. This is the Quaternary Period when climate fluctuated between very much colder than now and a little warmer than at present over many cycles of change. The cold periods are popularly known as the Ice Ages, although most authorities would agree that South-West England, including Dartmoor, was not covered by major ice sheets, as were more northern parts of Britain on at least three and probably more occasions. However, in the cold phases of the Quaternary, Dartmoor would have experienced tundra like conditions with permanently frozen ground that only melted in the surface layers during the summer months and remained frozen at depth. Because this made the sub-surface impermeable, there would have been much slumping and movement of the valley sides and the volume of flow in the rivers would have been much larger than at present in the summer ‘melt’ season and this would have helped in the carving of the deep gorge of the Dart. Furthermore, in the cold periods of the Quaternary, sea-level was perhaps up to 130 m lower than at present (because a significant proportion of water was locked up in the major ice sheets covering large parts of North America and North-West Europe), and this encouraged the rivers to down cut their courses.
As already stated, tors are classic features of the Dartmoor landscape and their form is controlled by the pattern of jointing (fractures) within them. Essentially where the joints are closely spaced, the granite is more easily broken down into finer material which if removed leaves the areas of less intensively jointed granite as upstanding blocks, i.e. tors. Classically, it is thought that the intensively jointed granite was broken down by chemical processes that were accelerated under climates that were significantly warmer than present in the period between 65 and 2.5 million years ago, and then the tors were exposed by stripping away of this rotted material in the cold phases of the Quaternary Period. Some authors, however, believe little chemical rotting was involved and that shattering by frost and downslope sludging of material in the cold phases of the Quaternary alone produced these landforms.
To claim this earth cache, please take a photo of yourself, or your GPS, set against a line of text from either of the two commandment stones. (optional, but very much appreciated) and upload it with your log.
Separately, please email us with the answer to the following questions.
1) Between 65 and 2 million years ago, Dartmoor was sub-tropical. Name a famous tree that grew on Dartmoor in that period.
2) In what year did William Whitely commission the engraving of the 10 commandments at Buckland Beacon?
3) What is the height above sea level from the top of the beacon?
4) Standing at the top of the Beacon, observe the Dart Valley. At what compass bearing can you best see how the River Dart has cut its way through the valley forming a noticeable gorge. Explain why you think the gorge may have formed.
5) From the top of the Beacon, you will see much evidence of slumping. At what compass bearing is the evidence of slumping most dense? From the Beacon, is it on the North West or South West facing aspect? Can you suggest a reason for this?
We express grateful thanks to Bruce Webb, Emeritus Professor, University of Exeter, for his invaluable and learned input into the above information.
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Additional Hints
(Decrypt)
Ab uvagf ner erdhverq.