LANDFORMS OF GLACIATED LOWLANDS

Landforms of glaciated lowlands are mainly depositional in nature, brought about by both valley glacier and continental ice sheets. The former leave behind the eroded material in only restricted areas. The imprint of ice sheets on the landscape is far more widespread because they advanced through large areas during the Ice Age, scouring and removing any surface soil and rock debris on their way. As a result, it has been estimated that almost a third of the total land surface of Europe and North America is littered with glacial and fluvio-glacial materials of all descriptions – moraines, boulder clay, tills, drifts, rock-flour, gravels and sands. Many of them are being re-eroded, resorted and redeposited elsewhere by present-day rivers.

Most of the glaciated lowlands have depositional features, but where rock masses project above the level surface, they result in striking features of erosion, such as the roche moutonnee and crag and tail.

 

1) Roche Moutonnee: This is a resistant residual rock hummock. The surface is striated by ice movement. Its upstream side is smoothed by abrasion and its downstream side is roughened by plucking, and is much steeper. The term roche moutonnee is used to describe such a feature because it resembles a sheepskin-wig once worn in France.

 

Roches moutonnees are found in both highland and lowland glaciated regions.

 

2) Crag and tail: The crag is a mass of hard rock with a precipitous slope on the upstream side, which protects the softer leeward slope from being completely worn down by the on-coming ice. It therefore has a gentle tail, strewn with the eroded rock debris. The classic example is the Castle Rock of Edinburgh, Scotland. Edinburgh Castle is located on the crag and the High Street on the tail.

The remaining glaciated lowland features are of a depositional nature. The following are the typical ones.

 

3) Boulder clay or glacial till: This is an unsorted glacial deposit comprising of a range of eroded materials – boulders, angular stones, sticky clay and fine rock- flour. It is spread out in sheets, not mounds, and forms gently undulating tills or drift plains: The landform is rather monotonous and featureless. The degree of fertility of such glacial plains depends very much on the composition of the depositional materials. Some of the boulder clay plains such as East Anglia and the northern Mid-West of U.S.A form rich arable lands.

 

4) Erratics: These are boulders of varying sizes that were transported by ice. They came with the advancing glacier or ice sheets, but when the ice melted, they were left ‘stranded’ in the regions of deposition. They are called erratics because they are composed of materials entirely different from those of the region in which they were found. Such erratics are thus most useful in tracing the source and direction of the ice movement. Sometimes, the erratics may be found perched in precarious positions just as the ice dropped them and they are then termed perched blocks. Examples of such blocks are commonly encountered in both lowland and highland areas in Europe e.g. Silurian grits are found perched on the carboniferous limestone of the Pennines. Their presence in large numbers is a hindrance to farming.

 

5) Drumlins: These are swarms of oval, elongated ‘whale-back’ hummocks composed wholly of boulder clay, with their elongation in the direction of the ice flow, that is on the downstream side. They are low hills varying from a few metres to 120 m (400 feet) in height and may be a kilometre or two long. They appear a little steeper at the onset side and taper off at the leeward end. They are arranged diagonally and so are commonly described as having a basket of eggs topography. Large numbers of them are found in County Down in Northern Ireland and the glaciated plain around the Great Lakes in North America.

 

6) Eskers: These are long, narrow, sinuous ridges composed of sand and gravel which mark the former sites of sub-glacial melt-water streams. They vary from a few metres to 60 m (200 feet) in height and may be several kilometres long. In some parts of Maine U.S.A, the outstanding eskers form a continuous ridge of 160 km (100 miles) ! They are very numerous in Scandinavia, e.g. the Punkaharju Esker of Finland. As eskers are made up of highly porous sand and gravel, water is rapidly drained off from their crests and they may not support many trees, though in Finland they often form tree-covered ridges between lakes.

 

7) Terminal moraines: These are made up of the coarse debris deposited at the edge of the ice-sheet, to form hummocky and hilly country such as the Baltic Heights of the North European Plain.

 

8) Outwash plains: These are made up of fluvio-glacial deposits washed out from the terminal moraines by the streams and channels of the stagnant ice mass. The melt-waters sort and re-deposit the materials in a variety of forms from the low hilly heathlands, such as the Luneburg heath of the North European Plain, to undulating plains, where terraces, alluvial fans and deltaic deposits of the melt-water stream make up the landscape. Kames, small rounded hillocks of sand and gravel, may cover part of the plain. There, the deposition takes the form of alternating ridges and depressions, the latter may contain kettle lakes and give rise to characteristic “knob and kettle’ topography.

 

The Human Aspects of Glaciated Landforms

Though the ice ages were at their height over 30,000 years ago, the effects of glaciation on both landforms and human activities have profound influence in many parts of the world today. Their most striking impact is felt in the temperate regions of Europe and North American which were once under continental ice sheets.

Further south and on the high mountains all over the world, slow-moving glaciers are still shaping the landscape in the Alps, Andes, Rockies and Himalayas. Glacial influences on man’s economic activities are both favourable and unfavourable, depending on the intensity of glaciation, the relief of the region and whether the effects are of an erosional or depositional nature.

In hilly regions such as the mountain slopes of Scandinavia, ice sheets and glaciers have removed most of the top soil, leaving them quite bare of vegetation. Soils that do exist are so thin that they are incapable of supporting effective agriculture. Glacial drifts in the valleys and benches or alps which were not affected by glaciers have good pastures during summer. Cattle are driven up to graze on the grass and return to the valley bottom in winter. This form of animal-migration type of farming is called transhumance.

Extensive boulder clay plains such as those of East Anglia and the Mid-West of U.S.A. are some of the most fertile agricultural plains known. The loess plains of Europe and Central U.S.A, with a high proportion of humus, are good farming land too. On the other hand, the sand or gravelly outwash plains e.g. the heath-covered geest of northern Germany, the marshy boulder clay deposits of central Ireland, the barren ice-scoured surfaces of the Canadian and Baltic Shields are infertile. The presence of numerous erratics and perched blocksin parts of Britain and in Alberta, Canada, many of them of gigantic size, obstruct farming and the use of machines. Morainic deposits may dam, or glaciers may hollow out lakes which greatly inconvenience large-scale farming or land development. But when the lakes are eliminated, the old glacial lake beds with their rich alluvium support heavy cropping.

Large lakes formed by former glaciation, e.g. the Great Lakes of North America, make excellent waterways. They may also cut deep overflow channels while draining off, making natural routeways across a mountainous terrain e.g. the Hudson-Mohawk Gap that links the interior with the Atlantic seaboard of U.S.A. On the other hand, in regions where drumlins are dominant, the drainage is either poor or much confused. Terminal and recessional moraines comprise coarse materials which are of little use to man but fluvio-glacial deposits are not without their economic significance. In the outwash plains, eskers and kames have been excavated to provide sands and gravels for highway and building construction.

The purest sands are extracted to make moulds for metal casting. The lake basins of glaciated mountains provide natural reservoirs. In countries like Scandinavia, Switzerland and Canada, where there is little available coal, streams and waterfalls that plunge down from hanging valleys or other glaciated uplands are being harnessed to provide hydroelectric power. This has helped to develop many of the chemical and metallurgical industries. With the magnificent scenery provided by the glaciated mountains e.g. the French, Italian and Swiss Alps, large numbers of tourists are attracted to them annually. Skiing, mountain climbing and sightseeing are all popular with Alpine tourists.