Lava in the Lakes -The Bowder Stone
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The Bowder Stone is a large piece of fine-grained, andesite lava from the Ordovician. (The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago)
One of Lakeland's most famous features, this 2000 ton, some 30 feet high, fifty feet across and ninety feet in diameter stone appears to rest in a state of delicate balance as you will see !. But, how did it get here ? did it topple down from the mountain side like most visitors assume?, or was it carried here from Scotland by the glaciers of the Ice Age ?
The stone belongs to the Borrowdale Volcanic Group of rocks, which are around 452 million years old. (which would support the latter theory perhaps)
Debate has focused on the geological reasons for its location. Two possible origins have been considered: that it was transported by ice and it is a glacial erratic boulder, OR it fell from the crags above. However the theory that it is a glacial erratic cannot be proven or disproven, there is no evidence that ice from Scotland ever penetrated the Lake District and the stone itself is a piece of Lake District volcanic rock, possibly from nearby Bowder Crag. Ice travelling down Borrowdale from the high fells could have brought the boulder but the Bowder Stone shows no signs of abrasion typical of glacial transport. Also, it is located in the Jaws of Borrowdale, where the valley narrows. Glacier movement speeds up in constricted areas and under such conditions glaciers are more likely to transport boulders rather than deposit them.
Rock fall ?
There is strong evidence that the Stone came to be at its present location because of a massive rock fall. The rock of the Stone and the material in the Hells Wall section of Bowder Crag are identical and its diamond cross-section reflects the pattern of joints in the rocks of Bowder Crag. Also, the rocks on part of Hells Wall have cleavage structures that mirror those on the two large standing stones, which at some time broke away from the Bowder Stone and now lie on its western side. The Stone is just one of many boulders lying on the slope below Bowder Crag and its position at the bottom of this slope is exactly where you would expect to find the largest boulder from a rock fall.
However there is no record of a massive rockfall occurring in historic times. The debris left by it is now completely stable and is today surrounded by dense scrubby woodland. The fall is thought to have occurred at the end of the last period of glaciation in the valley, between 13,500 and 10,000 years ago, when Bowder Crag, weakened by ice action, was subject to constant freeze thaw activity, we do know for definite that the stone is formed of Andesite lava, below is how it is formed:
Geological explanation of how LAVA is formed:
Lava, molten or partially molten rock that erupts at the earth’s surface. When lava comes to the surface, it is red-hot, reaching temperatures as high as 1200° C (2200° F). Some lava can be as thick and viscous as toothpaste, while other lava can be as thin and fluid as warm syrup and flow rapidly down the sides of a volcano. Molten rock that has not yet erupted is called magma. Once lava hardens it forms igneous rock. Volcanoes build up where lava erupts from a central vent. Flood basalt forms where lava erupts from huge fissures. The eruption of lava is the principal mechanism whereby new crust is produced lava is generated at depth, its chemical and physical characteristics provide indirect information about the chemical composition and physical properties of the rocks 50 to 150 km (30 to 90 mi) below the surface.
Most lava, on cooling, forms silicate rocks—rocks that contain silicon and oxygen. Lava is classified according to which silicate rocks it forms. If the silica content is between 65 percent and 50 percent by weight, then the lava is ANDESITIC, hence Andesite lava.
Whichever version you choose to believe the stone is a very impressive sight, both due to its sheer size and also the precarious position it now rests in, it doesn’t look like the full story of how this enormous piece of geological history will ever be revealed in full, but it certainly isn’t going anywhere and remains for us to ponder over today.
TO CLAIM THIS EARTHCACHE:
(research as well as visiting the stone will be required)
1.Please post a photo of yourself or your GPS with the stone
Please EMAIL ME the answers to the 2 following questions (not in your logs please):
1.What are the other 2 types of LAVA apart from ANDESITIC ?
2.Please give a description of the colour and texture to the touch of the boulder, also try to photograph any marks that you feel may be present from either the rock fall or glacial movement
PLEASE NOTE: I receive a very high number of Earthcache emails, I can’t reply to them all otherwise I’d be doing nothing else all day, as has always been the case there is no need to await a reply from me regarding your answers…. However due to numerous people thinking they can just log these caches without emailing any answers, and/or completing the required tasks these will be picked up, and the logs will be deleted without further communication. To facilitate this Please email your information either before, or AT THE SAME TIME OF LOGGING THE CACHE, Thanks.
(No hints available.)
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Coordinates are in the WGS84 datum