Upland areas are landscapes of erosion, Lowland areas are landscapes of deposition. Discuss the validity of this statement with reference to examples you have studied.

Glacial upland areas are characterised by a number of landforms. These include U-shaped valleys, cirques, aretes and pyramidal peaks. Many of these features can be seen in Figure 1. In all these features, the dominant producing factor is glacial erosion. These features can be found in many formerly glaciated areas, for example the area around Cwm Idwal in Snowdonia, Wales. The reasons glacial erosion is dominant in such areas are simple - colder temperatures, increased precipitation and a ready supply of ice.

There are many cirques in the Cwm Idwal area (cwm=cirque in Welsh) for example Cwm Cneiffon and Cwm Clyd. Cirques are formed when snow and ice accumulate in a hollow on a shaded part of a hillside (this is why all the cirques in the Cwm Idwal area face north east, out of the sun). Over the course of a year, the snow compacts further to form firn or nevee. This becomes further compressed into ice. The back wall (headwall) of the cirque is susceptible to frost-shattering activity, causing it to become very steep (e.g. the Devil's Kitchen behind Cwm Idwal in Snowdonia).

Rotational movement of the ice causes a semicircular shape to develop. Plucking or quarrying takes place towards the rear and abrasion at the base. However, cirques are not only features of erosion. Moraine (glacial debris) is pushed to the front and deposited to form a lip, which, after glacial retreat forms a dam causing a tarn (small lake) to develop.

Cwm Idwal itself is an example of a diffluent col or trough. A diffluent col was formed from an icefall, in this case when the icecap coming from the Arenig Mountains was forced to drop over an area of more resistant rocks between Y Garn and the Glyders.  This over-deepened the area it fell in, accentuating the existing syncline.

An arete (left) is a knife-edged ridge formed when two corries erode back to form a sharp knife-edged ridge, for example Crib Goch near Cwm Idwal. A pyramidal peak or horn can be formed when three of more corries erode back to form a peak, such as the Matterhorn in the Alps. (right)

Large U-shaped valleys, such as Nant Ffrancon or the Llanberis valley in Snowdonia are formed when large valley glaciers carve through the landscape, often with no reference to the existing geology.

Meso- and micro-scale features in upland areas also show signs of erosion, like striations and chattermarks where eroded material had been scraped along the bedrock and roches moutonnees, large rocks which have been subject to plucking on the upglacier side and abrasion on the down-glacier side.

Yet, although erosion is certainly the dominant process in upland glaciated areas, deposition still occurs. Most obviously large moraines are deposited by the glaciers, at the ends of glaciers (terminal moraines), at intermediate points of retreat (recessional moraine) or at the sides of glaciers (lateral moraines). There are a large number of moraines on the floor of Cwm Idwal, yet it is several hundred metres in elevation. Large erratics, such as those in Norborough can be deposited in upland areas when the glacier dumps its load.

Lowlands in formerly glaciated areas contain a variety of features for example moraines, drumlins, kames, eskers and kettle holes. The earliest explanation of the origins of glacial deposits was attributed to the Biblical flood. Ignatz Venetz (1821), Louis Agassiz (1837) and others first postulated the theory of glaciation.

Moraine is simply material dumped by a glacier after it retreats. This can take the form of terminal moraine, marking the furthest point the glacier reached, recessional moraine (subsequent temporary halts) or lateral moraine (along the sides of a glacier. Particularly prominent features called pro-talus ramparts can be formed if an icefall pushes moraine into a tall parapet, such as the moraines on the floor of Cwm Idwal.

Drumlins are egg-shaped hills, formed by the streamlining of moraine, although often with a rock core. Meltwater that escapes to the margin of a glacier will often deposit part of its load between the glacier and the valley wall. When the glacier retreats, the former streambed is left perched above the deglaciated valley floor. This distinctive landform is termed a terrace, specifically, a kame terrace.

Eskers are long winding ridges of glacial deposits formed from moraine deposited in sub-glacial streams. (Cross-section, left) Kettle holes are simply depressions formed when a block of ice left in the soil melts leaving a depression, often filled by a kettlehole lake.

All these features have a common theme of deposition; they are mainly formed by deposition and subsequent modification of ‘till’ or 'boulder clay'. However, lowland areas are not necessarily only areas of deposition.

In fact, the large amounts of glacial meltwater produced during glacial retreat can form dominantly erosive landscapes. For example the large, ‘flowerpot’ shape of the Gwaun valley in Snowdonia was formed as a result of meltwater erosion. Glacial meltwater can have enormous erosive power carving out large channels, which are now filled with misfit streams. The Treffgane Gorge was created by meltwater flowing in an overflow from a pro-glacial lake.  Interestingly a small ridge in the centre of the Gwaun valley acts as a watershed, with streams on either side flowing in opposite directions, although originally the meltwater would have all flowed in one direction under pressure.

Also, Knock and Lochan landscapes, such as those found in Scotland contain a variety of erosional features in lowland areas, such as rock drumlins.

In conclusion, although upland areas are largely erosive and lowland areas largely depositary, there is no 'clear cut' division. Although it is possible to draw a 'firn line' where ablation equals accumulation, there is still much erosion down-glacier and deposition up-glacier of the line. In particular, meltwater features have eroded many lowland areas while moraines can be found in upland areas.