If a topography that was shaped in earlier geological times, and subsequently covered by later deposits such as lava flow, marine sediments (provided the relief is less) or glacial debris or alluvium, is reexcavated and exposed so extensively that its characteristics are visible as a part of the present landscape, it will be called an exhumed surface.
The vast formation of Deccan basalt covered ancient gneiss granite or schist topography. The lava cover has been removed in some of the valleys but more particularly on the margins of the lava region in Maharashtra, Western Andhra Pradesh and Karnataka where the basaltic cover was thinner. Thus the pre-lava ancient crystalline topography is an exhumed surface.
It is believed that the Canadian Shield is mostly an exhumed surface which had been developed on Precambrian crystallines. The overlying mass of Palaeozoic sedimentaries has largely been removed and the exhumed surface has not been much altered since exhumation because of the highly resistant Precambrian rocks. Pleistocene glaciations have only ‘freshened’ the exhumed surface. The drainage shows a good deal of adjustment to Precambrian structure.
The Rockies, too, particularly the mountains of the Wyoming Basin are believed to have been eroded to humble dimensions (in extent and elevation) towards the end of the Tertiary period and the lower levels had been considerably covered by the eroded sediments. Pleistocene uplift has caused the exhumation of pre-Pleistocene topography. There are examples of exhumed surfaces in most countries of the world, e.g., northwestern Australia, in Central Massif of France and in Charnwood Forest region of England. Exhumed surfaces need not always be geologically ancient erosion surfaces. Even pre-Pleistocene surfaces exposed after the removal of Pleistocene cover may qualify as exhumed surfaces.
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Unconformities represent the junction of two geological structures in such a way that after the erosion of the older series circumstances particularly submergence favored the deposition of younger rocks on the older surface. If the unconformity is not very irregular but of rather level topography, the removal of the overlying younger series will bring into existence an exhumed surface. The possibility of an unconformity forming an exhumed surface is particularly great if the overlying cover mass is soft and the underlying older structure is resistant. The preservation of the exhumed surfaces is partly due to resistant lithological cover of the unconformity like laterite or sandstone silicified and converted into quartzite.
Some emphasize the significance of exhumed surface so much in geomorphology that they would prefer to have a distinct branch as Paleogeomorphology.