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Isostatic depression is the sinking of large parts of the Earth's crust into the
Isostatic depression is the sinking of large parts of the Earth's crust into the asthenosphere
The asthenosphere () is the mechanically weak and ductile region of the upper mantle of Earth. It lies below the lithosphere, at a depth between ~ below the surface, and extends as deep as . However, the lower boundary of the asthenosphere is not ...
caused by a heavy weight placed on the Earth's surface, often glacial ice
A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as ...
during continent
A continent is any of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven ...
al glaciation
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...
. Isostatic depression and isostatic rebound
Post-glacial rebound (also called isostatic rebound or crustal rebound) is the rise of land masses after the removal of the huge weight of ice sheets during the last glacial period, which had caused isostatic depression. Post-glacial rebound ...
occur at rates of centimeters per year. Greenland is an example of an isostatically depressed region.
Glacial isostatic depression
Isostatic depression is a phase of glacialisostasy
Isostasy (Greek ''ísos'' "equal", ''stásis'' "standstill") or isostatic equilibrium is the state of gravitational equilibrium between Earth's crust (or lithosphere) and mantle such that the crust "floats" at an elevation that depends on its ...
, along with isostatic rebound
Post-glacial rebound (also called isostatic rebound or crustal rebound) is the rise of land masses after the removal of the huge weight of ice sheets during the last glacial period, which had caused isostatic depression. Post-glacial rebound ...
. Glacial isostasy is the Earth's response to changing surface loads of ice and water during the expansion and contraction of large ice sheets. The Earth's asthenosphere acts elastically, flowing when exposed to loads and non-hydrostatic stress, such as ice sheets, for an extended period of time. The Earth's crust is depressed by the product of thickness of ice and the ratio of ice and mantle densities. This large ice load results in elastic deformation of the entire lithospheric mantle over the span of 10,000-100,000 years, with the load eventually supported by the lithosphere after the limit of local isostatic depression has been attained. Historically, isostatic depression has been used to estimate global ice volume by relating the magnitude of depression to the density of ice and upper mantle material.
Glacial megalakes can form in regional depressions under the influence of glacial load.
Isostatic depression in Greenland
Greenland is isostatically depressed by theGreenland ice sheet
The Greenland ice sheet ( da, Grønlands indlandsis, kl, Sermersuaq) is a vast body of ice covering , roughly near 80% of the surface of Greenland. It is sometimes referred to as an ice cap, or under the term ''inland ice'', or its Danish equi ...
. However, due to deglaciation Deglaciation is the transition from full glacial conditions during ice ages, to warm interglacials, characterized by global warming and sea level rise due to change in continental ice volume. Thus, it refers to the retreat of a glacier, an ice she ...
induced by climate change, the regions near the shrinking ice sheet have begun to uplift, a process known as post-glacial rebound
Post-glacial rebound (also called isostatic rebound or crustal rebound) is the rise of land masses after the removal of the huge weight of ice sheets during the last glacial period, which had caused isostatic depression. Post-glacial rebound a ...
. Modeling these glacial isostatic adjustments has been an area of interest for some time now as the entire topography of Greenland is affected by these movements. These movements are unique in that they can be observed on a human time scale unlike other geological processes. Models have been created to assess what future equilibrium states of the Greenland ice sheet will look like.
See also
*Proglacial lake
In geology, a proglacial lake is a lake formed either by the damming action of a moraine during the retreat of a melting glacier, a glacial ice dam, or by meltwater trapped against an ice sheet due to isostatic depression of the crust around th ...
*Subsidence
Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope move ...
*Isostatic rebound
Post-glacial rebound (also called isostatic rebound or crustal rebound) is the rise of land masses after the removal of the huge weight of ice sheets during the last glacial period, which had caused isostatic depression. Post-glacial rebound ...
*Greenland ice sheet
The Greenland ice sheet ( da, Grønlands indlandsis, kl, Sermersuaq) is a vast body of ice covering , roughly near 80% of the surface of Greenland. It is sometimes referred to as an ice cap, or under the term ''inland ice'', or its Danish equi ...
*Forebulge
In geology, a forebulge is a flexural bulge in front as a result of a load on the lithosphere, often caused by tectonic interactions and glaciations. An example of forebulge can be seen in the Himalayan foreland basin, a result of the Indian-Eura ...
*Deglaciation Deglaciation is the transition from full glacial conditions during ice ages, to warm interglacials, characterized by global warming and sea level rise due to change in continental ice volume. Thus, it refers to the retreat of a glacier, an ice she ...
*Asthenosphere
The asthenosphere () is the mechanically weak and ductile region of the upper mantle of Earth. It lies below the lithosphere, at a depth between ~ below the surface, and extends as deep as . However, the lower boundary of the asthenosphere is not ...
References