Topography and Geology

The topography of a region is often strongly influenced by the underlying geology. Flat-lying sedimentary layers have a different topographic expression from folded strata, and igneous rocks can also be quite distinctive. Two good examples are the Valley and Ridge province of Pennsylvania, and the Black Hills of South Dakota.

(Click on any image to view a larger versions of the images)

Top: Digital topography of the Valley and Ridge province.
Bottom:Digital Geologic map of the Valley and Ridge province.

The Valley and Ridge formed approximately 250 million years ago when Europe and Africa collided with North America. Sediments on the edge of the North American continent were bent and deformed into a series of large folds. Because the different types of sedimentary rocks have different strengths, they erode differentially with the more resistant layers forming the ridges and the softer sediments underlying the valleys. In South Dakota an ancient igneous intrusion pokes through the continental crust, forming a large dome in a landscape that is otherwise rather flat. This large topographic feature is also a result of the erosional resistance of granite compard to the surrounding sedimentary sedimentary rocks.

Top: Digital Topography of the Black Hills.
Bottom:Digital Geologic map of the Black Hills.

Topography and Geologic History
Many events in the Earth's geologic history leave characteristic topographic imprints. Large meteorite impacts such as those at Meteor Crater in Arizona, or Manicouagan Quebec, are easily recognizable by their distinctive topography.

photo of manicouagan impact crater
topography showing manicouagan crater
Top: Manicouagan impact crater, photo taken from space courtesy of NASA.
Bottom: Digital topography of the Manicouagan impact crater.

topography of the fingerlakes and grand canyon fingerlakes and grand canyon topography The Finger Lakes region of New York state is another example of topography that provides clues to the geologic past. The long, linear shape of the Finger Lakes is due to gouging by glaciers when large continental ice sheets advanced from the Arctic to cover the area 18,000 years ago. The Grand Canyon provides evidence of more than three million years of erosion by the Colorado River.
Top: Digital topography of the Finger Lakes region of New York State.
Bottom: Digital topography of the Grand Canyon.		  

 

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