Mejoras y Resultados

Rocks formed during all the geological time periods can be found in Greenland. West Greenland is dominated by Precambrian crystalline basement consisting of rocks such as gneiss, granite and schist that represent old fold belts. Younger fold belts are found in North and East Greenland (Fig. 30) where undeformed sedimentary and volcanic rocks are also widespread.

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NOMINATION OF THE ILULISSAT ICEFJORD

IN THE SUNSET THE ICEBERGS CHANGE COLOUR

Photo: Jakob Lautrup, GEUS

Fig. 30. Simplified geological map of Greenland.

The bedrock of the Ilulissat Icefjord area consists of crys- talline rocks, and is dominated by grey gneiss with minor intercalations of amphibolite. Gneiss is a banded meta- morphic rock that was formed under high pressure and temperature deep in the crust of the Earth. The gneiss around Ilulissat Icefjord is orthogneiss and was formed from igneous rocks, presumably granites.

The rocks are of Precambrian age and formed during collision between two continents about 2000 million years ago. At this time, a number of small old continents collided and amalgamated to form one of the earliest major continents on Earth. The rocks represent the

deepest parts of an alpine fold belt and are strongly defor- med, showing folding and dipping strata. Many kilome- tres of rock that formed the upper levels of the fold belt and lay above the present land surface have been eroded away. During the last 500 million years, Greenland has moved progressively towards the pole, from the tropics to its present Arctic latitude (Fig. 31).

On the island of Disko, west of Ilulissat, Cretaceous sedi- ments and a thick pile of Tertiary plateau basalts are found. These rock types possibly also once covered the Ilulissat Icefjord region, but have been eroded away because of land uplift during the last few million years.

Climate

A high-pressure system prevails over the Greenland Inland Ice. This, in combination with the orographic influence of Greenland, means that westward moving low-pressure systems can be forced to move northward along the west coast of Greenland. Most precipitation in West Greenland is related to the passage of such low-pressure systems (Hansen 1999).

The town of Ilulissat has a continental type of climate. The mean July temperature is 7.5°C, measured over the

61 3. DESCRIPTION 5 25 2 2 2 2 40 80 100 120 120 7 50 2 0

Fig. 31.The geographical position of Greenland has changed over the millennia as a result of plate tectonic movements, which has also led to the opening of the Atlantic Ocean.The numbers indicate time in million years before the present.

Solid ice

Solid ice Ice edge Open water

Sun Ice conditions Month Mean precipi- tation (mm) Temperature ˚C

Winter Spring Summer Autumn

Jan. 15 -13,5 -15,0 -14,5 -8,5 -0,5 5,0 7,5 6,5 2,5 -3,5 -8,0 -11,5 Feb. 15 Mar. 15 Apr. 20 May. 20 June 25 July 30 Aug. 30 Sep. 40 Oct. 25 Nov. 25 Dec. 15

Fig. 32. Distribution of sunlight, sea ice conditions, temperature and precipitation during an annual cycle in the Disko Bugt area.

Source: Modified from Gunver Krarup Petersen.

time period from 1961 to 1990 (Fig. 32). It is thus situ- ated in the low-arctic bio-climatic zone, which can be defined by a mean temperature for the warmest month between 5 and 10°C. The highest mean temperature re-

corded during the period was 10.3°C. Ilulissat is character- ised by low winter tempera- tures, and the coldest month is March with a mean tempera- ture of –19.9°C. The lowest (mean) temperature recorded is –24.7°C. The mean annual precipitation is only 266 mm, and August/ September has most precipitation, but the yearly variations are small. Calm days are quite frequent, especially during the summer, but the storms can be quite violent. The highest mean wind velocities are found in the wintertime, with a highest mean wind velocity of 22.1m/s recorded in Janua- ry 1992. Stormy weather occurs in connection with passa- ges of low pressure systems, or in connection with føhn winds, which are relatively warm and dry winds with a westerly direction from the Inland Ice to the outer coast. During a period with føhn winds, the temperature can increase 10–20°C over a few hours, and the air becomes unusually dry. Føhn winds during the winter can lead to widespread thaw of snow and ice, but the føhn normally lasts for a short period only, after which a return to normal weather conditions is seen. In the winter period, this can lead to the formation of a widespread crust of ice on the snow surface. Since 1880, when systematic ob- servations began, marked changes in the climate have oc- curred. Most notably, an increase in the mean winter air temperature of c. 4.5°C was recorded between 1900 and

1925. The summer temperatures also increased, although on a smaller scale. The temperature rise was a conse- quence of increased inflow of warm Atlantic air masses from the south, but it was enhanced by the albedo effect as a consequence of reduced sea ice formation.

Over the past decades, the area has been characterised by falling temperatures. This is the opposite of the general trend over the Northern Hemisphere, where a marked warming is observed. However, the cooling in West Greenland may now have ceased (Anonymous 2002c). Ilulissat is located north of the Arctic Circle and thus has a winter period when the sun does not rise above the hor- izon, and a period during the summer when the sun is above the horizon all 24 hours. However, the altitude of the sun is always low, which is why the polar regions are the coldest parts of the Earth.