Glacial formations

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The contrasting influence of the two main rock formations on the landforms of the National Park has already been referred to. The Old Red Sandstone is relatively resistant to weathering, and forms rugged mountainous country. Various forms of erosion have worn down the Carboniferous rocks to form a low-lying plain.

Apart from the nature of the rock formations, the strongest influence on the landforms of the area was Quaternary ice movements. While the smooth summit ridges of Mangerton, Purple and Tomies Mountains may represent pre-glacial surfaces that stood above the ice as nunataks, the predominant landforms of the mountain area are those of glacial erosion. At high levels, erosion by frost and ice carved out horseshoe-shaped corries, some now filled by lakes, such as the Devil’s Punchbowl.

At lower levels pre-glacial valleys, including the major valley now containing the Upper Lake and Long Range, were deepened by glaciers, most recently those that advanced north-eastwards during the last glaciation. Many rock surfaces were moulded and striated by the passing ice.

In the lowlands, landforms derived from glacial deposition predominate. The widespread glacial drift material include large crescentic terminal moraines north of Lough Leane and irregular kame and kettle-hole deposits east of Muckross Lake, laid down by the ice when it reached the limestone lowlands and subsequently retreated. In addition to extensive sand and clay deposits, there areoccasional erratic rocks.

Deposits laid down beneath the ice and at its edge as it retreated also occur locally at the edge of and within the mountain area. Fretted cliffs and caves along the limestone lake shores are the results of limestone solution by lake waters, possibly combined with the earlier effects of glacial meltwaters and ice erosion. The same combination probably formed the basins of the lakes themselves.

A small lake in Dromyrourk townland, similar to turloughs elsewhere, has seasonal changes of water level controlled by water levels in underground drainage channels in the limestone.