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Plate boundary Mountains
> O-O convergent - one plate slides under the other
andesitic and basaltic magmas rise to form island arcs such as
Japan and Indonesia
- a deep trench that forms is eventually thrust up and folded into a
mountain chain
- O-C convergence - ring of fire
- C-C convergence - Himalayas
- O-O divergent - Mid Atlantic
Ridge > rising magma pressures up the central
rift due to its temperature and decreased density > cooling causes the
older crust to settle and crack
Isostasy - when one mass of a particular geologic structure
floats upon the mass of another due to differences in density that result
in buoyancy
> therefore a mountain must have a large root upon which it floats
in the mantle
> there is usually 5/6 root to 1/6 mountain above
ground (similar top icebergs)
Densities H2O = 1
> continental crust 2.8
> ocean crust basalt = 2.9
> upper mantle = 3.3
An interesting aspect of
isostasy is that erosion can wear away massive overburden and a resulting
rebound will occur
After the last Glacial Ice Sheet melted away the
subtending land mass began to gradually rise and in many places are still
rising (rebound) such as the Holland Marsh area.
More Technical Details>>>>>
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