Most of us already know that large scale topographic feature, like mountains, are formed by plate-tectonic activates.
If two plates of almost same density collide with each other, the intermediate parts (most likely filled by earlier sediments) compress and bulge up. This kind of phenomenon is occurred in case of continent-continent collision. The Himalayan region is an example of such continent-continent collision. If two plate diverges, then negative space is created. Results in negative topography. This is a popular phenomenon near mid-oceanic ridges, where due to extension, oceans (negative tectonic topography) are formed. . Above said topographies are compensated at a certain depth of mantle. So, they are in isostatic equilibrium. Such topography does not change quickly in geological time scale. However, these are not only way to effect the topography on surface. Mantle flow below the lithospheric plates contributes significant surface topography. This topography may change with time, depending on the mantle flow and its convective stress. That is why, this is named as Dynamic Topography. Dynamic topography is low in amplitude, but wavelength is large. Suppose a rigid plate is floating on viscous mantle. If the underlying mantle is hot and buoyant, it will up well and a divergent flow will create vertical upward force. This will create a positive topography on the surface of the earth. If a mantle plume comes up, positive dynamic topography is expected. Opposite to it, mantle underlying the crust, could be dense. This can create a convergent flow. At the boundary of the crust-mantle, it creates a vertical downward flow followed by depression. Overlying surface follows the depression and gives rise a negative dynamic topography. Dynamic topography is calculated as observed topography minus isostatic topography. That is why, it is also called as residual topography. For details: Braun 2010, Nature Geoscience
1 Comment
Geo_stu
11/30/2016 02:49:42 pm
Interesting
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