geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...

, lithospheric flexure (also called regional isostasy) is the process by which 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 ...

(rigid, thin outer layer of the Earth) bends under the action of forces such as the weight of a growing

orogeny Orogeny () is a mountain-mountain formation, building process that takes place at a convergent boundary, convergent plate margin when plate motion compresses the margin. An or develops as the compressed plate crumples and is tectonic uplift, u ...

or changes in ice thickness related to

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 ...

. The lithosphere rests on 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 ...

, a viscous layer that in geological time scales behaves like a

fluid In physics, a fluid is a liquid, gas, or other material that may continuously motion, move and Deformation (physics), deform (''flow'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are M ...

. Thus, when loaded, the lithosphere progressively reaches an isostatic equilibrium, which represents

Archimedes' principle Archimedes' principle states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially, is equal to the weight of the fluid that the body displaces. Archimedes' principle is a law of physics fun ...

applied to geological settings. This phenomenon was first described in the late 19th century to explain the shorelines uplifted in

Scandinavia Scandinavia is a subregion#Europe, subregion of northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. ''Scandinavia'' most commonly refers to Denmark, Norway, and Sweden. It can sometimes also ...

by the removal of large ice massed during the last glaciation. American geologist G. K. Gilbert used it to explain the uplifted shorelines of Lake Bonneville.Lake Bonneville" US Geological Survey Monograph No. 1
1890. 438 p. The concept was not retaken until the 1950s by Vening Meinesz. The geometry of the lithospheric bending is often modeled adopting a pure

elastic Elastic is a word often used to describe or identify certain types of elastomer, Elastic (notion), elastic used in garments or stretch fabric, stretchable fabrics. Elastic may also refer to: Alternative name * Rubber band, ring-shaped band of rub ...

thin plate approach (sometimes by fitting the gravity anomaly produced by that bending rather than more direct data of it). The thickness of such plate that best fits the observed lithospheric bending is called the ''equivalent elastic thickness'' of the lithosphere and is related to the stiffness or rigidity of the lithosphere. These lithospheric bending calculations are typically performed following the Euler-Bernoulli bending formulation, or alternatively the Lagrange equation.

References

Geodynamics {{geophysics-stub