Geology


  THE ICE SHEET - THE ICE CAP

Some 65 millions ago Greenland had a very warm climate.

This time period is known as the start of the Tertiary period. Fossils of plants related to magnolia and breadfruit tree indicate an almost sub-tropical climate in Greenland then!

Possibly the Earth's climate was hotter then, but Greenland was really located much further south! Later, plate tectonic movements slid it further north.

At the end of the Tertiary period the climate turned both colder and wetter.

That's when glaciers began to form in the coastal mountain regions of Greenland. The land surface of Greenland is bowl-shaped with high mountains towards the coasts and a flat terrain between.

Because of heavy snowfall glaciers started forming in the mountains along the edges of the island, and they slowly spread inland as the years passed. Over time this created the ice sheet (or ice cap as it is called today) as we know it now - covering 85% of Greenland.

Learn more

   
  MAPPING GREENLAND'S GEOLOGY
  Below are two interactive maps to explore the geology of Greenland!
 

Geological Map of Greenland from GEUS

  Click the map to enlarge
  Explore Greenland's Geology in GIS
   
  GREENLAND DRIFTING AWAY

Asia, Europe and America were one land continent 100 million years ago.

Then this vast landmass split apart, and the space between the different pieces of the landmass is what is now the Atlantic Ocean.

What became America - including Greenland - is still moving very slowly westward.

The reason continents change position relative to each other is because they rest on giant plates, which slide very slowly over a softer zone under the Earth's crust.

This re-positioning of continents is not peaceful. When a moving plate collides with another it crumples the continents into mountain chains. Collision zones exist today, and this is places where major earthquakes occur.
   
 
  GLACIERS

GlacierIce is somewhat plastic.

For example, ice is under pressure from ice and snow layers above, it will flow out towards the edge.

This means that there is constant movement of the ice sheet in the ice cap. In most places this movement is very slow, for example in the large unified ice sheet. However, at the edges of the ice cap movement is easily visible as glaciers!

Here ice movements of 3 feet (one meter) per day are very common. But there are also examples of glaciers that move much faster - amongst these is the well-known Illulissat Glacier, which glides at a speed of 180-225 feet (20-25 meters) a day, making it the fastest moving glacier in the world.

This high level of activity is possible because glaciers follow long deep valleys - valleys that often continue into deep fjords.


The extent of the ice cover fluctuates with the climate. The Greenland climate was mild during the 20th century when compared to the previous century and especially mild since 1930. The warmer climate has caused most glaciers to retreat. This can be clearly seen in the form of large moraine heaps some distance beyond the present ice edge, and by freshly smoothed out terrain in front of the ice sheet...

Explore what glaciers do to the landscape

   
   
Greenland Geology Dramatic rocky landscapes, distinctive fold structures in a rock wall, beautiful minerals and fossils millions of years old, that is all part of Greenland's geology!

Greenland is famous for being the largest island in the world-but actually Greenland is sort of like a continent...

More than anything else, the geology of Greenland - the landscape of Greenland - has been and still is shaped by the great ice sheet.

Today Greenland's ice sheet covers more than 85% of the island. That means, just 15% of Greenland is not covered by ice.


Bedrock - the Precambrian

Earth's earliest rocks were formed some 4,500 to 570 million years ago! So long ago it is hard to grasp, this time is called the Precambrian period - and the rock is what is called bedrock.

BedrockBedrock is the foundation on which Greenland is built. Almost all of southern Greenland is still bedrock today. Bedrock is made up of the two rock types: granite and gneiss.

In other areas of Greenland, over the long periods of time, other layers have been formed on top of this bedrock as a result of geological processes-changes to the landscape caused by events... at the Earth's surface, inside of Earth or off the Earth, like falling meteorites landing on Earth! Examples of event on Earth's surface are: weathering (breakdown of rock), landslides, and erosion by running water or glaciers! Events inside of Earth could be earthquakes and volcano eruptions!

The layers that cover the bedrock on Greenland can be lavas, or sediments - decomposed products such as clay and sand, or calcareous shells from small creatures, which are turned through time into shale, sandstone and limestone respectively as a result of pressure due to deep burial under later layers.

These sedimentary layers can be extremely thick, up to 6 miles (10 km) deep - but then in some places the layers are broken down again by erosion (wearing away of rock), so that it is now down to bedrock again!

Nowadays bedrock is actually the dominant rock type in the ice-free areas of Greenland!


Different Kinds of Bedrock


Not all bedrock is the same-because it was not all formed at the same time!

The oldest part - the ancient core - is found on the west coast between Paamiut and Kangerlussuaq. In a location northeast of Nuuk, bedrock has been dated as being at least 3,700 millions years old. That means it is the oldest of any rocks found on Earth!!

The youngest section of the ancient core is 'only' 2,500 million years old.

South of this area lies the younger bedrock, the Ketilidian. This is 1,800 to 1,500 milion years old.

North of the ancient core - right up to Qaanaaq - are the Nagssugtoqidian, formed during the same period as the Ketilidian.

Geology timelineBoth the Ketilidian and the Nagssugtoqidian are made up of materials from the ancient core, so in reality it is all ancient core but done forming at different ages!

Bedrock only lies exposed in a few places in northern Greenland, where it has been covered by formations from later times.

While bedrock is mostly made up of the two rock types granite and gneiss, there are also other types of rock in bedrock. In many places in Greenland gneiss and granite walls have distinctive dark bands of another rock type: dolerite dykes! Delorite dykes happen when magma from the inside of earth forces its way upwards though cracks in the bedrock! Magma is fluid, very hot material (molten rock) located beneath earth's crust, inside of earth-the kind of stuff that comes out of a volcano: lava is a river of magma!

Explore the time before the Precambrian period - From Palaeozoic, to Mesozoic to Cenozoic



DID YOU KNOW...


CrevasseCrevasses

The inner part of the ice cap is a single large unified sheet. But in many places out near the rim of the ice cap, crevasses 90-120 feet deep (30-40 metres) deep can be found. A crevasse, a crack in the ice sheet, most often comes to be because of ice movement over the underground terrain.


NunatakNunataks


Out towards the rim mountain peaks stick up through the ice. In Greenland - and everywhere else - these are called nunataks.