Post-glacial rebound

Postglacial land uplift or isostatic land uplift is the rise of those land masses called that were covered during the last Ice Age to the Holocene of ice. The effect occurs mainly in Scotland, northern Europe ( Fennoscandian land uplift ) and Eastern Siberia, Canada and Alaska.

Causes and expiration

Northern Europe, Eastern Siberia (Western Siberia was only slightly glaciated ) and North America more than 11,000 years ago for centuries of up to 3 km thick ice sheets covered. The mass of the ice allowed the affected Earth's crust sink into the mantle. The liquid components of the viscous mantle flowed then from the side and arched so the crust outside the ice cap on.

When the glaciers melted away by the end of the Pleistocene and early Holocene and began thus to reduce the ice pad it came to reverse processes: The jacket materials flowed back toward the center of the former ice sheet and it established a uplift of the earth's crust. Outside the expansion territories of the former ice, however, began lowering operations. Due to the enormous strength of the shell of this compensation process will continue for several thousand years until isostatic equilibrium is reached. The extent of postglacial land uplift is dependent on the viscosity of the mantle and the vertical extent of the former ice sheet.

Studies have shown that this uplift proceeded in two temporal 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 elevation decreased to 25 mm per year and is continuing on. Today's elevation varies by region and is about 10 mm per year.

From the uplift history of isostatically rising land masses, the strength of the mantle can be estimated. Corresponding elevation models provide a mean dynamic viscosity of 1021 Pa · s

Effects

The effects of postglacial land uplift consist of vertical and horizontal crustal movements. In combination, there is thus changes the inclination of the earth's surface. There are other effects that result from the vertical and horizontal crustal movements. Their registration is a problem of theoretical physical geodesy. The following table is intended to provide an overview of impacts and applicable measurement procedures:

Overview

• GNSS ( absolute and relative)
• Leveling (relatively)
• Level measurements ( relative)

• GNSS ( absolute and relative)

• Level measurements ( relative)
• Satellite altimetry

• Terrestrial gravity measurements ( Gravimeters)
• Satellite missions, such as "Grace"

• VLBI

• Seismograph

Examples

The postglacial land uplift affected the topography of the abovementioned regions. Instance, the Swedish Lake Mälaren was a bay of the Baltic Sea, which was cut off by the uplift. In Denmark there is a north central tilt axis ( Ringkøbing - Fyn - threshold ) to a land uplift, while the southern part and northern Germany subside. The same applies to the north and south of the UK. Together with the expected rise in sea level due to the greenhouse effect, this reduction could result in the area of the Thames estuary to threatening floods.

In North America, the postglacial land uplift had a decisive influence on the development of the Great Lakes. The upper lake was formerly with the Lake Michigan and Lake Huron part of a huge lake. The land uplift led to the separation in three waters.