Lakes of the Lake District: Difference between revisions

===Plucking and abrasion===

The whole process of ice excavation can be described in fairly simple terms, when in reality, it involves a complex set of stages working together. Essentially, the movement of glaciers' grinds and pulls apart the bedrock on which it sits. Dr Alan Smith's book, ''The Big Lakes of Lakeland'', describes this process clearly, without over complicating an already complex set of processes. With nowhere else to go except to follow the flow of ice, the broken pieces of rock were then transported as the ice moved along the valleys, in the case of the Lake District, radially in an outward direction from a central core. This core was so thick that maybe only the tips of the highest peaks of [[Scafell]], [[Bowfell]], and [[Great Gable]] were visible.<ref name="smith12">Smith, ''Big Lakes of Lakeland'', p.12</ref> The Last Glacial Maximum was approximately 22,000 years ago and up to that point in time, the ice had been steadily increasing until it reached its maximum, hence the name. All the big lakes were excavated by the ice during this Last Glacial Maximum, a segment of the Last Glacial Period, which encompassed a timeframe between 115,000 - 11,700 years ago. By 13,550 years ago, the ice sheets had retreated and the "valley glaciers had melted away and a new landscape of ice scoured fells and lakes left impounded in the valley floors was revealed."<ref name="smith12"/>

 

So, what is plucking? Plucking is a process that removes large fragments of rock under immense pressures and moves them to other locations, sometimes lengthy distances from their original position. This is similar to quarrying, except instead of explosives and heavy machinery, ice does all the hard work. For plucking to be most effective, '''Fracturing''' needs to take place. This is a separate process that weakens the bedrock along naturally occurring joints and fractures, prior to being broken up.<ref name="smith13">Smith, ''Big Lakes of Lakeland'', p.13</ref> As Dr Smith explains, these weaknesses in the rocks may be enough for the ice break away these weakened fragments. However, not all rocks were made equal, and because of this, harder and softer rocks are broken up differently. As the upper layers of bedrock are plucked, the lower layers of rock 'relaxes' and 'unloads' as the pressure of weight is relieved.<ref name="smith13"/> This then results in the lower layers eventually fracturing and weakening for further plucking to take place. This cycle could repeat for many thousands of years.