isostatic rebound - definition - English
Isostatic rebound (also called continental rebound, post-glacial rebound or isostatic adjustment) is the rise of land masses that were depressed by the huge . Rapid isostatic rebound during deglaciation caused the sea to fall relative to the land along the southern British Columbia coast. .. date commonly accepted for the last glacial maximum . The ''relaxation time'' (deﬁned by. The regional isostatic uplift of southern Alaska is on a scale large enough to conclusion that the regional uplift is dominated by isostatic rebound associated with the Occupation dates are listed for the temporary tide gauge sites. . The combination of well-defined raised shorelines and robust stands of.
The ice sheets at the last glacial maximum were so massive that global sea level fell by about metres. Thus continental shelves were exposed and many islands became connected with the continents through dry land.
A sub-continent also existed between Siberia and Alaska that allowed the migration of people and animals during the last glacial maximum. During deglaciation, the melted ice water returns to the oceans, thus sea level in the ocean increases again.
However, geological records of sea level changes show that the redistribution of the melted ice water is not the same everywhere in the oceans.
In other words, depending upon the location, the rise in sea level at a certain site may be more than that at another site.
This is due to the gravitational attraction between the mass of the melted water and the other masses, such as remaining ice sheets, glaciers, water masses and mantle rocks  and the changes in centrifugal potential due to Earth's variable rotation.
The situation in North America is less certain; this is due to the sparse distribution of GPS stations in northern Canada, which is rather inaccessible.
That is, locations farther north rise faster, an effect that becomes apparent in lakes. The bottoms of the lakes gradually tilt away from the direction of the former ice maximum, such that lake shores on the side of the maximum typically north recede and the opposite southern shores sink.
Tilting of land will also affect the flow of water in lakes and rivers in the future, and thus important for water resource management planning. Gravity field[ edit ] Ice, water and mantle rocks have massand as they move around, they exert a gravitational pull on other masses towards them.
This change in the topography of Earth's surface affects the long-wavelength components of the gravity field. Since postglacial rebound continuously deforms the crustal surface and the gravitational field, the vertical datum needs to be redefined repeatedly through time.
State of stress, intraplate earthquakes and volcanism[ edit ] According to the theory of plate tectonicsplate-plate interaction results in earthquakes near plate boundaries. However, large earthquakes are found in intraplate environment like eastern Canada up to M7 and northern Europe up to M5 which are far away from present-day plate boundaries. An important intraplate earthquake was the magnitude 8 New Madrid earthquake that occurred in mid-continental US in the year Glacial loads provided more than 30 MPa of vertical stress in northern Canada and more than 20 MPa in northern Europe during glacial maximum.
This vertical stress is supported by the mantle and the flexure of the lithosphere. Since the mantle and the lithosphere continuously respond to the changing ice and water loads, the state of stress at any location continuously changes in time.
The changes in the orientation of the state of stress is recorded in the postglacial faults in southeastern Canada.
Post-glacial rebound - Wikipedia
This shows that the stress due to postglacial rebound had played an important role at deglacial time, but has gradually relaxed so that tectonic stress has become more dominant today. According to the Mohr—Coulomb theory of rock failure, large glacial loads generally suppress earthquakes, but rapid deglaciation promotes earthquakes.
Thus, both postglacial rebound and past tectonics play important roles in today's intraplate earthquakes in eastern Canada and southeast US. Generally postglacial rebound stress could have triggered the intraplate earthquakes in eastern Canada and may have played some role in triggering earthquakes in the eastern US including the New Madrid earthquakes of Increasing pressure due to the weight of the ice during glaciation may have suppressed melt generation and volcanic activities below Iceland and Greenland.
On the other hand, decreasing pressure due to deglaciation can increase the melt production and volcanic activities by times. Recent rise in sea levels has been monitored by tide gauges and satellite altimetry e.
The rate of rebound or subsidence has to be added to or subtracted from the raw observations made by, for example, tide gauges see the Permanent Service for Mean Sea Level website for more information. Sea-level measurements will be affected by rebound or subsidence of the solid Earth. But the rebound of the Earth is not the only complicating factor when we try to measure how much sea level is rising.
The reason for this variation is gravity. Gravity is the force which pulls two masses towards each other; the larger the mass, the greater the attraction. This is why the ocean stays stuck to the Earth — because the Earth is a very large mass.
Melting Glaciers Are Wreaking Havoc on Earth’s Crust
Now, the distribution of mass throughout the Earth is not uniform, so the pull of gravity is not the same everywhere. Courtesy of the European Space Agency. See here for a video Solid Earth Shape Figure 5: Cartoon showing how the change in the shape of the geoid and the rebound of the solid Earth following the melting of an ice sheet results in non-uniform sea-level change.Interaction between Climate, Volcanoes, and Isostatic Rebound
From Tamisiea et al. The reason that this complicates our measurements of sea-level change is because when an ice sheet melts it alters the distribution of mass on the surface of the Earth, and this alters the shape of the geoid. In addition, the rebound of the solid Earth beneath the former ice sheet alters the distribution of mass within the Earth, also altering the shape of the geoid. As the meltwater enters the ocean, it follows the new geoid shape, and since this shape differs from the shape before the ice sheet melted, the sea-level rise is not uniform .
When the sea level observations from tide gauges and raised shorelines are considered together with the GPS data, the total combined data set provides an exceptional record of the regional uplift. Each data set is examined separately within the context of a simple two-layer viscoelastic earth model subjected to a model of ice load changes that are independently constrained by airborne laser altimetry Arendt et al.
The regional isostatic uplift of southern Alaska is on a scale large enough to allow determinations of upper mantle asthenosphere viscosity and lithosphere elastic thickness. The ultimate goal of the present study is to test various earth models against all of the uplift observations. Specifically, we restrict this effort to a single load model that is built upon observations of glacial change, rather than iteratively constrained by the uplift data themselves.
Given the rheological simplicity of a linear Maxwell solid, the results provide robust constraints of lithospheric and asthenospheric structure, as well as the statistically significant conclusion that the regional uplift is dominated by isostatic rebound associated with the post-LIA deglaciation of southern Alaska.
Tide Gauge Data and Error Analysis We have augmented sea level rates found at four permanent tide gauges Larsen et al.
Temporary tide gauges typically record sea level over the course of one or more monthly tidal cycles, and the elevation of the gauge is then surveyed relative to a local network of benchmarks.
Mean sea level at the site is calculated and referenced to the benchmarks. When this procedure is repeated some years later, sea level change can be found relative to the benchmarks. Temporary tide gauges are primarily installed to assist in the charting of waterways for navigational purposes by the NOS. Of the data presented here, all of the initial occupations and half of the repeat occupations were performed by NOS field crews.