Willy Fjeldskaar and Aleksey Amantov: Present Uplift in Norway Due to Glacier Unloading Since the ‘Little Ice Age’

SCC Volume 2.3.

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 glaciers of late-glacial time. The mountain glaciers of Norway have previously not been considered to affect the present rate of uplift. We have now calculated the effect of the decaying glaciers since the Little Ice Age and found that the effect is a significant factor in the ongoing rate of uplift in Norway.

While the last huge sheet over Scandinavia melted away around 9 000 years ago, a cooling trend (Neoglaciation) some thousand years later was responsible for the establishment and growth of the Norwegian mountain glaciers. After several periods of glacier growth and decay most Norwegian glaciers probably culminated in mid 1700s AD during the Little Ice Age. From the Little Ice Age the glaciers started to decay and finally ended at the present thicknesses of the glaciers. We calculated both the isostatic and elastic response 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. There are thus 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 = 0.7x 1011N/m2. This unloading of the Norwegian glacier over the last 300 years lead to present rate of uplift in glaciated areas of more than 2.0 mm/yr in the areas of mountain glaciers.

Continue reading: Present Uplift in Norway Due to Glacier Unloading Since the
’Little Ice Age’. By Willy Fjeldskaar and Aleksey Amantov