SCIENCE of
CLIMATE CHANGE

International Journal of Science and Philosophy

Present uplift in Norway due to glacier unloading since the ‘Little Ice Age’

Authors

  • Willy Fjeldskaar, Tectonor AS, Stavanger, Norway
  • Aleksey Amantov, VSEGEI, St. Petersburg, Russia

Abstract

The observed present rate of uplift in Scandinavia increases from zero on the western coast of Norway to ~1 cm/yr in the Baltic Sea area. This domelike uplift is generally assumed to be the result of glacial isostasy due to melting of the huge glacier in Late Pleistocene. The mountain glaciers of Norway have previously not been considered to affect the present rate of uplift. However, we have now calculated the effects of the decaying glaciers since the Little Ice Age (LIA) and found that these effects are a significant part of the ongoing rate of uplift in Norway.

The last huge inland glacier in Scandinavia melted away around 9 000 years ago, followed by a warm climate that prevailed in some 3 000 years. After this warm period came a cooling trend (Neoglaciation) in which mountain glaciers established. After several periods of glacier growth and decay most Norwegian glaciers probably culminated in mid 1700s AD during the LIA. From the LIA, the glaciers started to decay and finally ended at the present thicknesses.

We calculated both the isostatic and elastic responses of the unloading of the mountain glaciers. When a force (positive or negative) is applied to the Earth’s surface, there is an immediate elastic deformation pro­portional to the stress. This will be followed by a time-dependent isostatic response. The elastic displacement is gradually recovered as the Earth adjusts toward isostatic equilibrium. When isostatic equilibrium is achieved, there will be no elastic deformation. Thus, there are basically two causes of elastic effects: (l) loading/unloading of ice caps, (2) isostatic movements caused by the loading/unloading.

The isostasy is calculated with a low-viscosity asthenosphere of 1.8 x 1019 Pas and an effective elastic lithosphere thickness Te ~ 30 km. The elastic modelling assumes the shear rigidity (μ) of 0.7 x 1011 N/m2. The calculations show that the unloading of the Norwegian mountain glaciers over the last 300 years lead to the present rate of uplift in the glaciated areas of more than 2.0 mm/yr.

 

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Present uplift in Norway due to glacier unloading since the ‘Little Ice Age’

Description

Abstract

The observed present rate of uplift in Scandinavia increases from zero on the western coast of Norway to ~1 cm/yr in the Baltic Sea area. This domelike uplift is generally assumed to be the result of glacial isostasy due to melting of the huge glacier in Late Pleistocene. The mountain glaciers of Norway have previously not been considered to affect the present rate of uplift. However, we have now calculated the effects of the decaying glaciers since the Little Ice Age (LIA) and found that these effects are a significant part of the ongoing rate of uplift in Norway.

The last huge inland glacier in Scandinavia melted away around 9 000 years ago, followed by a warm climate that prevailed in some 3 000 years. After this warm period came a cooling trend (Neoglaciation) in which mountain glaciers established. After several periods of glacier growth and decay most Norwegian glaciers probably culminated in mid 1700s AD during the LIA. From the LIA, the glaciers started to decay and finally ended at the present thicknesses.

We calculated both the isostatic and elastic responses of the unloading of the mountain glaciers. When a force (positive or negative) is applied to the Earth’s surface, there is an immediate elastic deformation pro­portional to the stress. This will be followed by a time-dependent isostatic response. The elastic displacement is gradually recovered as the Earth adjusts toward isostatic equilibrium. When isostatic equilibrium is achieved, there will be no elastic deformation. Thus, there are basically two causes of elastic effects: (l) loading/unloading of ice caps, (2) isostatic movements caused by the loading/unloading.

The isostasy is calculated with a low-viscosity asthenosphere of 1.8 x 1019 Pas and an effective elastic lithosphere thickness Te ~ 30 km. The elastic modelling assumes the shear rigidity (μ) of 0.7 x 1011 N/m2. The calculations show that the unloading of the Norwegian mountain glaciers over the last 300 years lead to the present rate of uplift in the glaciated areas of more than 2.0 mm/yr.