Glacial rebound

From GeoClasses

Below, is an image taken from the website: http://ilrs.gsfc.nasa.gov/science_analysis/atmos.html

Glacial rebound (sometimes called continental rebound, isostatic rebound or isostatic adjustment) is the rise of land masses that were depressed by the huge weight of ice sheets during the last ice age, through a process known as isostatic depression.

Post-glacial rebound has caused numerous significant changes to coastlines and landscapes over the last several thousand years, and the effects continue to be significant.

By the end of the last ice age about 11,000 years ago, much of northern Europe and North America was covered by ice sheets up to 3 km thick. The enormous weight of this ice caused the crust to sink into the fluid mantle. At the end of the ice age when the glaciers retreated, the removal of the weight from the depressed land led to a rapid uplift due to the buoyancy of crustal material relative to the mantle. Due to the extreme viscosity of the mantle, it will take many thousands of years for the land to reach an equilibrium level.

Studies have shown that the uplift has taken place in two distinct stages. The initial uplift was rapid, proceeding at about 7.5 cm/year. This phase lasted for about 2000 years, and took place as the ice was being unloaded. Once de-glaciation was complete, uplift slowed to about 2.5 cm/year, and decreased exponentially after that. Today, typical uplift rates are of the order of 1 cm/year or less, and studies suggest that rebound will continue for about another 10,000 years. The total uplift from the end of deglaciation will be about 400 m.

Post-glacial rebound has caused numerous significant changes to coastlines and landscapes over the last several thousand years, and the effects continue to be significant. In Sweden, Lake Mälaren was formerly an arm of the Baltic Sea, but uplift eventually cut it off and led to it becoming a freshwater lake in about the 15th century. Marine seashells found in Lake Ontario sediments imply a similar event in prehistoric times. In several Nordic ports, like Tornio, the harbour had to be relocated several times in the past centuries.

In Great Britain, glaciation affected Scotland but not Southern England, and the post-glacial rebound of northern Great Britain is causing a corresponding downward movement of the southern half of the island. This is leading to an increased risk of floods, particularly in the areas surrounding the lower River Thames. Along with rising sea levels caused by global warming, the post-glacial sinking of southern England is likely to seriously compromise the effectiveness of the Thames Barrier, London's most important flood defence, after about 2030.

The Great Lakes of North America lie approximately on the 'pivot' line between rising and sinking land. Lake Superior was formerly part of a much larger lake together with Lake Michigan and Lake Huron, but post-glacial rebound raised land dividing the three lakes about 2,100 years ago. Today, southern shorelines of the lakes continue to experience rising water levels while northern shorelines see falling levels.

Globally, post-glacial rebound was tending to make the earth more spherical over time. However, this effect has been reversed by other factors such as large scale movements of ocean water caused by El Niño and related effects.

In order to measure the ongoing deformation in wMBL, there are three continuously recording, autonomous GPS stations (Global Positioing System) (Similar to the satellite positioning system found in many newer model automobiles today) on outcrops in wMBL with baselines of ~100-200 km. The stations will gather data for at least four years, and are being installed in concert with a series of autonomous stations in the Transantarctic Mountains, resulting in an unprecedented long baseline array across the Ross Embayment.

Nunatak east of Mount Carbone, Phillips Mountains, western Marie Byrd Land

http://en.wikipedia.org/wiki/Hailuoto

Hailuoto, an island and a municipality in the province of Oulu, Finland is located on an island of the same name opposite the city of Oulu in the Gulf of Bothnia. A ferry operates regularly between Hailuoto and Oulunsalo. In winter an official ice road connects the island to the mainland.

Land in the region is constantly rising due to post-glacial rebound. It is estimated that the first parts of Hailuoto appeared from the Baltic Sea about 1700 years ago. Current island of Hailuoto was formed from the merge of many smaller islands. Two large sections, Santonen and Hanhinen merged into the main island (Luoto) only about two centuries ago. The island is continuously expanding and eventually it will join with the continent. Kirkkosalmi, a wetland region between Hanhinen and Luoto is renowned being a very important bird refuge where plenty of rare bird species are observed.

This is an image of the Aletsch glacier, in Switzerland. This image was taken from: http://en.wikipedia.org/wiki/Glacier

Exam Question

The initial uplift was rapid, proceeding about 7.5 cm/year. This phase lasted about 2,000 years, and took place as the ice was being unloaded. Once de-glaciation was complete, uplift slowed to about how many cm/year?

References

Most of the information/images/material on this page, was gathered from http://en.wikipedia.org/