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Underneath the Mountains
These lecture notes discuss the role of buoyancy, flexure, and erosion in the earth's topography and the lifetime of mountain ranges. It recalls Pascal's law that pressure of a material overlying a fluid is equal everywhere at a given depth and Archimedes' principle that a body in a fluid is buoyed up with a force equal to the weight (mass x volume) of the displaced fluid. Continents are buoyant crust floating on denser mantle, so a 4 km high mountain range must have a 20 km deep root. According to Archimedes' principle, when mountain ranges erode, pressure is released from the surface and the mountain root is bouyed up to equalize the pressure. Continental crust is about 40 km thick, so it is strong enough to support smaller topographic loads, like small volcanoes, without the aid of a buoyant root.
Intended for grade levels:
  • High (9-12)
  • College (13-14)
  • College (15-16)
Type of resource:
  • Visual:
    • Illustration - scientific
  • Text:
    • Ref. material
  • Geological Sciences:
    • Geology
Technical requirements:
No specific technical requirements, just a browser required
Cost / Copyright:
No cost
Copyright 2005 Board of Regents of the University of Wisconsin System
DLESE Catalog ID: SERC-NAGT-000-000-000-814
Resource contact / Creator / Publisher:
Contact: University of Wisconson, Madison, Department of Geology and Geophysics