The term dynamic topography is used in
geodynamics
Geodynamics is a subfield of geophysics dealing with dynamics of the Earth. It applies physics, chemistry and mathematics to the understanding of how mantle convection leads to plate tectonics and geologic phenomena such as seafloor spreading, ...
to refer the elevation differences caused by the flow within Earth's
mantle.
Definition
In geodynamics, ''dynamic topography'' refers to
topography
Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the landforms and features themselves, or a description or depiction in maps.
Topography is a field of geoscience and planetary sci ...
generated by the motion of zones of differing degrees of
buoyancy
Buoyancy (), or upthrust, is the force exerted by a fluid opposing the weight of a partially or fully immersed object (which may be also be a parcel of fluid). In a column of fluid, pressure increases with depth as a result of the weight of t ...
(convection) in
Earth's mantle.
It is also seen as the residual topography obtained by removing the
isostatic contribution from the observed topography (i.e., the topography that cannot be explained by an isostatic equilibrium of the crust or 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 ...
resting on a fluid mantle) and all observed topography due to
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 an ...
. Elevation differences due to dynamic topography are frequently on the order of a few hundred meters to a couple of kilometers. Large scale surface features due to dynamic topography are
mid-ocean ridge
A mid-ocean ridge (MOR) is a undersea mountain range, seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading ...
s and
oceanic trench
Oceanic trenches are prominent, long, narrow topography, topographic depression (geology), depressions of the seabed, ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers ...
es.
[ Other prominent examples include areas overlying ]mantle plume
A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic ho ...
s such as the African superswell. For a recent review of observational and modelling constraints on dynamic topography, see Davies et al. (2023).
The mid-ocean ridges are high due to dynamic topography because the upwelling hot material underneath them pushes them up above the surrounding seafloor. This provides an important driving force in plate tectonics
Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...
called ridge push: the increased gravitational potential energy
Gravitational energy or gravitational potential energy is the potential energy an object with mass has due to the gravitational potential of its position in a gravitational field. Mathematically, it is the minimum Work (physics), mechanical work t ...
of the mid-ocean ridge due to its dynamic uplift causes it to extend and push the surrounding lithosphere away from the ridge axis. Dynamic topography and mantle density variations can explain 90% of the long-wavelength geoid after the hydrostatic ellipsoid is subtracted out.[
Dynamic topography is the reason why the geoid is high over regions of low-density mantle. If the mantle were static, these low-density regions would be geoid lows. However, these low-density regions move upwards in a mobile, convecting mantle, elevating density interfaces such as the core-mantle boundary, 440 and 670 kilometer discontinuities, and the Earth's surface. Since both the density and the dynamic topography provide approximately the same magnitude of change in the geoid, the resultant geoid is a relatively small value (being the difference between large but similar numbers).][
]
Examples
The geological history of the Colorado Plateau during the last 30 million years has been considerably affected by dynamic topography. At first, between 30 and 15 million years ago, the plateau was greatly uplifted. Then, in a second phase, between 15 and 5 million years ago the plateau was tilted to the east. Finally, in the last 5 million years the western part of the plateau has been tilted to the west. The plateau would have reached its high elevation of 1,400 m.a.s.l. due to dynamic topography.
In Patagonia a Miocene
The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
transgression has been attributed to a down-dragging effect of mantle convection. A subsequent regression in the Late Miocene and Pliocene and further Quaternary
The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...
uplift in the eastern coast of Patagonia may in turn have been caused a decrease in this convection.
See also
* Epeirogenic movement
*Mountain formation
Mountain formation occurs due to a variety of geological processes associated with large-scale movements of the Earth's crust ( tectonic plates). Folding, faulting, volcanic activity, igneous intrusion and metamorphism can all be parts of th ...
*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 ...
References
*
{{Refend
External links
* Discussion on th
definition of dynamic topography
Geodynamics
Oceanography