Tarns of the Lake District: Difference between revisions
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==Cirque tarns==
These are small bodies of water usually formed in mountainous hollows or corries, known also as glacial cirques. These are bowl-shaped, ice-excavated rock basins, some of which are naturally deep, once carved by millions of tonnes of ice, erosion and weather. Cirques typically have three steep sides containing a headwall and two enclosing sidewalls, with a fourth being more open where a glacial till or moraine (rock debris that formed a dam) eventually enclosed and trapped the remaining ice.<ref name="smith24">Smith, p.24</ref> Some of the best examples of a cirque tarn are [[Blea Water]], [[Angle Tarn (Langdale)]], [[Stickle Tarn]] (below image), [[Blind Tarn]] and [[Scale Tarn]].
These mountainous tarns are unlike their lower altitude relatives found in the outlying fells (and various other locations in the northwest) where they look more like large ponds. While a number of these will be natural, others will be man-made, once serving different industrial purposes. ▼
<div class="res-img-1200">[[File:Stickle Tarn from Pavey Ark.jpg]]{{c|<small>[[Stickle Tarn]] as seen from the heights between [[Harrison Stickle]] and [[Pavey Ark]]</small>}}</div>
The typical characteristics of cirque tarns resemble a pudding bowl, some definitely more circular than others. This bowl will have a single deep point, usually in or near the centre, some of which are very deep for their size. A prime example of this is [[Blea Water]], just north of the [[Kentmere]] valley and west of [[Haweswater]] Reservoir. It has a depth of 63 metres (206 feet), almost twice the depth of [[Grisedale Tarn]] at 33 metres (108 feet). The next deepest is [[Red Tarn]] at 26 metres (85 feet), and [[Easedale Tarn]] at 22.5 metres (74 feet).<ref>Smith, p.27</ref> The moraine can also affect how deep the tarn is, depending on how much debris was moved during the "ice action" of its excavation.
Cirque tarns do come in a variety of shapes and sizes, not all of these being the typical shape one would expect to see. Those that stand out, mentioned above, were formed because the land under the ice dome during the last glacial period, paired with the radial (outward) flow of ice, meant that certain geological processes made the shaping of them possible. There are upwards of 200 cirque type features, yet, one would be surprised to see that of this large number, only 19 hold water.<ref name="smith24"/> Some cirque basins did, historically, hold water but have now either dried up, primarily due to the sedimentary infilling from the various becks that flowed into them. At the end of the last glacial period, the landscape would have looked very different, scarred, barren, devoid of life, and the number of cirque tarns would have been greater. In the last 13,000 years, these have been reduced dramatically and lost to history. Yet the evidence of infilling is still very much apparent as seen at [[Blind Tarn Moss]] near [[Grasmere]], and at [[Dry Cove Moss]] near [[Weatherlam]],<ref>Smith, p.36</ref> where the outline of the cirques now reveal a peaty wetland. It is only a matter of time before the tarns will all but disappear because of the same infill process. That is, unless human intervention disrupts that natural progression.
▲These mountainous tarns are unlike their lower altitude relatives found in the outlying fells (and various other locations in the northwest) where they look more like large ponds. While a number of these will be natural, others will be man-made, once serving different industrial purposes.
==List of tarns==
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