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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 c. below the surface, and extends as deep as . However, the lower boundary of the asthenosphere i ...
caused by a heavy weight placed on the Earth's surface, often glacial ice during continent
A continent is any of several large geographical regions. Continents are generally identified by convention (norm), convention rather than any strict criteria. A continent could be a single large landmass, a part of a very large landmass, as ...
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 be ...
. 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 wikt:ἴσος, ''ísos'' 'equal', wikt:στάσις, ''stásis'' 'standstill') or isostatic equilibrium is the state of gravity, gravitational mechanical equilibrium, equilibrium between Earth's crust (geology), crust (or lithosph ...
, 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 sheet
In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacier, glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice s ...
s. The Earth's 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 c. below the surface, and extends as deep as . However, the lower boundary of the asthenosphere i ...
acts viscoelastically, flowing when exposed to loads and non-hydrostatic stress, such as ice sheets, for an extended period of time. The Earth's crust
Earth's crust is its thick outer shell of rock, referring to less than one percent of the planet's radius and volume. It is the top component of the lithosphere, a solidified division of Earth's layers that includes the crust and the upper ...
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
A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...
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 the Greenland ice sheet. However, due to deglaciation induced by climate change, the regions near the shrinking ice sheet have begun to uplift, a process known aspost-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 an ...
. 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 *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 mov ...
*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
* Forebulge
* Deglaciation
*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 c. below the surface, and extends as deep as . However, the lower boundary of the asthenosphere i ...
References