The land below and around the ice

The geology of Greenland reflects a history that stretches back over nearly four billion years. By far the greatest part of the sub-continent is made up of crystalline rocks of the Precambrian shield. Fjords and valleys that cross the present day shield were formed by river erosion and later deepened by glacial erosion during the many advances and retreats of the Inland Ice. The glaciers also erode the landscape today, as can be seen at the ice margin around Ilulissat.

Precambrian shield at Godthåbsfjorden, West Greenland. Typical crystalline rocks are grey gneisses with layers of black amphibolite.

The Precambrian shield of West Greenland consists dominantly of crystalline gneiss basement, formed during several periods of mountain building, and welded together. The oldest rocks about 3.9 billion years old occur in the Isua region to the south, whereas the area around Ilulissat is formed by younger rocks about 1.8-1.6 billion years old.

The Precambrian shield is dominated by pale grey, folded, gneisses and granites, with bands and enclaves of mica schist and dark basic rocks. The bedrock is widely exposed along the whole of the ice-free part of western and southern Greenland, but the Inland Ice conceals the bedrock of 81% of Greenland.

Some of the oldest rocks in the world are found at Isua, north-east of Nuuk, the capital town of Greenland. The 3.8 billion-year-old rocks contain the earliest signs of life on Earth in the form of carbon thought to be produced by miro-organisms. (Photo: M. Rosing, Geologisk Museum)

Cliff section showing lava flows from the upper lava series on Disko, West Greenland. The photograph shows a section through eight flows with similar construction. The flows are 20-40 metres thick. (Photo: L.M. Larsen)

Some of the oldest rocks in the world are found at Isua, north-east of Nuuk, the capital town of Greenland. Here the mountains contain 3.9 billion-year-old rocks that have been intensively investigated by geologists, and which contain the earliest signs of life on Earth in the form of carbon thought to be produced by micro-organisms. Evidence has also been found for plate tectonic processes even at this early time. The ancient rocks around Isua are bounded by younger crust formed 2.5 billion years ago, with to the north and the south still younger rocks formed 1.8 to 1.6 billion years ago. The bedrock between Kangerlussuaq and the inner part of the Disko Bugt region, comprises both 2.5 billion years and 1.8-1.6 billion years old rocks that were formed deep down in the Earth’s crust.

Together with North America, Greenland formed a large North American continent, 1.6 billion years ago. At that time the folding in the Precambrian mountain ranges in Greenland was more or less complete, and the shield had risen and was partly eroded. Later developments largely involved the marginal parts where rocks formed later are preserved in North Greenland, East Greenland and parts of central West Greenland. Two large fold belts were formed along the coasts of North and North-East Greenland 400-350 million years ago.

Greenland’s subsequent geological development was dominated by the formation of sedimentary basins along the margins of the Precambrian shield, where 5-10 kilometre thick successions of sediments were deposited. These deposits are preserved today in coastal areas, with the thickest successions offshore on Greenland’s continental shelf. The sedimentary rocks on Disko, and the peninsula of Nuussuaq north of Disko Bugt, were formed 120-60 million years ago. The rock types include deposits from rivers and lakes and marine sediments deposited off the then coast.

Tectonic plate movements 60-55 million years ago led to the opening of the Atlantic, when Greenland was separated from Norway and northern Europe. Meanwhile the Labrador Sea and Davis Strait resulted from movements along a spreading axis between Canada and West Greenland. Sea-floor spreading was accompanied by profuse volcanic activity along the rupture zones, and the resulting km-thick volcanic successions are preserved today on Disko, Nuussuaq and Svartenhuk Halvø in West Greenland, and in the central part of East Greenland. Similar lava-successions are widespread on the sea floor offshore West and East Greenland.


Simplified geological map of Greenland. Click on the image to enlarge it.

Drainage channels, troughs and fjords

Kangia is eroded through an area of Greenland’s Precambrian shield formed 1.8 billion years ago. The mineral compositions of the rocks indicate they recrystallised at depths of 20-30 km and temperatures of 400-700°C. Uplift and erosion has brought these once deeper-lying crystalline rocks up to the present day land surface.


Cross-section showing how the base of the lithosphere is depressed during mountain building. As the tops of the mountains gradually erode, the load on the underlying asthenosphere decreases, so the remaining rocks in the mountains rise gradually upwards and material in the asthenosphere flows inwards. (Illustration: Carsten E. Thuesen) Click on the image to enlarge it.

Before the Inland Ice covered Greenland, rivers played an important role in the early formation of the valley that became the site of Kangia and the trough under Sermeq Kujalleq. The rivers eroded valleys that extended right out to the edge of the continental shelf. The watershed lay in the eastern part of Greenland, such that a substantial proportion of the precipitation that fell over Greenland drained westwards towards Disko Bugt. River erosion must have led to the formation of major valleys.

As the Inland Ice began to cover Greenland, a large part of the precipitation continued to drain towards Disko Bugt, but now in the form of glacier ice. The major ice streams followed the major valleys that had been formed by the rivers. Large glaciers such as Sermeq Kujalleq can erode broad and deep troughs, where the bottom lies far under sea level. The ice itself is not a very effective erosion agent, but rocks and boulders at the base of the glacier are pushed over the bedrock under the considerable weight of the ice and cause the glacier to act like a gigantic file. It is in this way that the large glaciers around Disko Bugt have formed Egedesminde Dyb, Kangia and the trough under Sermeq Kujalleq.

Water depths in Disko Bugt and Davis Strait. The Egedesminde Dyb trench between Qeqertarsuaq and Aasiaat marks the position of a former ice stream.

Glaciers are responsible for creating many of the spectacular fjords around the world. The Ilulissat area is particularly important as one of the few localities on Earth where the power of active glaciers in eroding fjords and the potential of meltwater forming drainage channels can be seen at the present day.

Moraine ridges, kame terraces and marginal deltas

A large part of the rock material eroded from the trough beneath Sermeq Kujalleq and Kangia has been deposited on the sea floor over thousands of years. There are also moraine ridges on land, and a well-developed system of moraine ridges can be traced over the land from one fjord to the next, stretching almost without a break from Qasigiannguit and Ilimanaq in the south via the iceberg bank to the mouth of Paakitsoq fjord.

The earliest moraines were deposited 9500 years ago, when the relative sea level was 60-70 metres above the present day sea level. A later moraine system formed 8000 years ago, when the relative sea level was 35-50 metres above that of the present day. The disposition of the moraines and the shallow water depths over Isfjeldsbanken indicate that the calving front of the forerunner of Sermeq Kujalleq was considerably smaller then than it is today, and the production of calf ice must have been similarly smaller.

Moraine ridges are formed during pauses in the retreat of the ice front or during short re-advances. Features such as kame terraces and marginal deltas are also formed at the ice margin. All three landscape forms can be seen in areas around the present ice margin near Ilulissat, areas from which the ice has disappeared over the course of the past 150 years.

Continue your journey through Ilulissat Icefjord:

The ice, the science and the Icefjord

Major moraines (red lines) in the Ilulissat region. The moraines related to ice recession are shown in pink. Marine deposits are shown in blue and lake sediments in green. The former (19th century) extent of Sermeq Kujalleq (Jakobshavn Isbræ) is shown with blue-grey horizontal lines. Marine deposits are shown in blue and freshwater deposits in green. Reproduced from a published 1974 map sheet, that uses the former Danish names for Qasigiannguit (Christianshåb), Ilimanaq (Claushavn), Ilulissat (Jakobshavn), Kangia (Jakobshavn Isfjord) and Sermeq Kujalleq (Jakobshavn Isbræ). Click on the image to enlarge it.

Marginal moraine ridge in the mountain area north of Kangia (Ilulissat Icefjord). The moraine, with a person standing on the top, is part of a system of ice margin features that extend from Isfjeldsbanken and further north.

Land uplift

When an ice sheet disappears, the land rises. Signs of land uplift can be seen at many places in Europe and North America. The Swedish ‘Hôga Kusten’ is an exceptional example. During the ice ages, Scandinavia and large parts of northern Europe were covered by the Fennoscandian ice sheet. The ice sheet was three kilometres thick and depressed the Earth’s crust in central Scandinavia by at least 800 metres.

Greenland is a present-day analogy to the Swedish ‘Höga Kusten’, in that the three-kilometre thick Inland Ice depresses the crust below the inner part of Greenland to about the same extent as central Scandinavia during the last ice age. The area around Kangia is reminiscent of Sweden’s ‘High Coast’ during the ice age, apart from the fact that the present ice-free coasts have undergone uplift following the retreat of the Inland Ice margin from its former maximum extent.


Cross section of Greenland, showing the thickness of the Inland Ice. In the central part the ice is more than 3 kilometres thick. Note that the deepest part of the ice is lying below sea level. Flow lines show how the ice is moving from the inner parts towards the margin (Illustration: Carsten E. Thuesen). Click on the image to enlarge it.

The last ice age culminated 21,000 years ago, and the world’s ice sheets have subsequently either disappeared or diminished in size, with the consequent contribution of meltwater causing the level of the world’s oceans to rise by 135 metres. Areas of Greenland that were once covered by ice have been raised above sea level due to uplift. In West Greenland, for example, the presence of raised marine and coastal deposits in the present day ice-free land areas are evidence of land uplift.

In the western part of the Ilulissat area the highest coastline dating from the end of the ice age is 70 m above the present sea level. There are raised marine deposits in several places, for example at Sermermiut, where sand deposits contain shells of marine bivalves.


Map showing the amount of uplift since the end of the last glacial 11,700 years ago. Click on the image to enlarge it.

When the ice advances and retreats

The repeated advances and retreats of the ice sheet margin have created many small-scale landscape features.

  • Many of the valleys in the area around Ilulissat are glacially modified river valleys, like the icefjord itself. The valleys are formed in zones where rocks with many joints and fractures can more easily be eroded by waterand ice.
  • Roches moutonées (literally ‘sheep rock’) are asymmetrical bedrock mounds, with a smooth rounded stoss side and a steep rough lee side. They are formed when the ice slides over the terrain, grinding to form the rounded side, while the rough side is formed when the ice plucks stones and boulders out of the bedrock.
  • A characteristic feature of the area around Kangia are the numerous lakes that lie in hollows formed by glacial erosion. Their great concentration and random location reflect the strongly irregular relief.
  • Erosion marks such as glacial striae are formed by stones embedded in the base of the ice sheet, and are formed as the ice moves so that the striae are parallel to the movement direction of the ice. These striations were pre­s­- umably formed during the period prior to the last deglaciation of the area, which took place around 9500 - 5000 years ago.
  • So-called perched boulders are conspicuous in many places. These are large blocks or boulders that rest in an often unstable position on rock surfaces, where the retreating, melting ice left them. They are not usually found in areas close to sea level, where breaking waves can disturb them.
  • Newer ice front features include the so called ‘trim lines’, on rock surfaces that mark the surface of an earlier glacier. Beneath the trim line the rock surface is light and without lichen growth, while the rock above the line (not covered by the earlier glacier) is darker and covered by lichen and other plants.

North side of the front of the glacier, with trim line. The light coloured vegetation-poor zone was formerly covered by an extension of the glacier. Dark coloured rocks in the background (above the trim line) are covered with lichens and other plants.