Postglacial land elevation
Post-glacial uplift or isostatic uplift is the name given to the rise of the land masses that were covered by inland ice during the last Ice Age up to the Holocene . The effect occurs mainly in Scotland , Northern Europe ( Fennoscandic uplift ) and Eastern Siberia as well as in Canada and Alaska .
Causes and process
Northern Europe, Eastern Siberia (Western Siberia was only slightly glaciated) and North America were covered by ice sheets up to 3 kilometers thick for centuries more than 11,000 years ago . The mass of the ice caused the affected crust to sink into the mantle . The liquid components of the viscous earth's mantle then flowed off to the side and thus arched the earth's crust outside the ice armor.
When the glaciers melted at the end of the Pleistocene and the beginning of the Holocene and the ice cover began to decrease, reversal processes occurred: the mantle materials flowed back towards the centers of the former ice sheets and the earth's crust began to lift. On the other hand, subsidence processes began outside the expansion areas of the former ice. Due to the enormous toughness of the jacket, this equalization process will take several thousand years until an isostatic equilibrium is reached. The extent of the postglacial land uplift depends on the viscosity of the earth's mantle and the vertical extent of the former ice sheet.
Studies have shown that this uplift occurred in two phases. In the first phase, which was completed about 2000 years ago, the uplift was up to 75 mm per year. With the beginning of the second phase, the uplift decreased to 25 mm per year and it continues to decrease. Today's uplift varies from region to region and is around 10 mm per year.
The tenacity of the earth's mantle can be estimated from the history of uplift of isostatically rising land masses . Corresponding uplift models provide an average dynamic viscosity of 10 21 Pa · s.
Effects
The effects of the postglacial land uplift are vertical and horizontal crustal movements. In combination, there are changes in the inclination of the earth's surface. There are other effects that result from the vertical and horizontal movements of the earth's crust. Their registration is a problem of theoretical physical geodesy . The following table is intended to provide an overview of the effects and applicable measurement methods:
overview
| impact | Geodetic measuring methods | comment |
|---|---|---|
| Vertical crust movements |
|
GPS network "BIFROST" |
| Horizontal crust movements |
|
GPS network "BIFROST" |
| Changes in global sea water levels |
|
|
| Changes in the Earth's gravitational field |
|
point-by-point measurement area measurement |
| Change in the earth's rotation (and influence on pole migration) |
||
| Tensions / earthquakes (especially intra-plate quakes) |
Examples
The postglacial land elevation influences the topography of the aforementioned regions. The Swedish lake Mälaren was a bay in the Baltic Sea that was cut off by uplift. In Denmark there is a land uplift north of a central tilting axis (Ringkøbing-Fünen-Schwelle) ( living spaces on the Nivåbugt ), while the southern part and northern Germany are sinking . The same applies to the north and south of Great Britain . Together with the expected rise in sea level due to the greenhouse effect , this lowering could lead to threatening floods in the Thames estuary area.
Web links
- Explanations on the BIFROST project for the derivation of velocity vectors for the postglacial land uplift in Fennoscandia
- About the land uplift and the history of the Baltic Sea in "Planet Wissen"
- Information and map of the Swedish Lantmäteri (Swedish)
Individual evidence
- ↑ G. Kaufmann, K. Lambeck: Glacial isostatic adjustment and the radial viscosity profile from inverse modeling . In: Journal of Geophysical Research . 107, No. B11, 2002, p. 2280. bibcode : 2002JGRB..107.2280K . doi : 10.1029 / 2001JB000941 . PDF