Geoscience Reference
In-Depth Information
Growing mountains
Continental crust
40 km
8 km
Magma
Ocean
Magma
Oceanic crust
Moho level
Lithosphere
Asthenosphere
Increased mass moves uppermost
mantle down, asthenosphere sinks
(a)
Continental mass
decreases due
to erosion
ecreas
to erosi
a
ecreas
o eros
s
creas
to ero i
Sediments deposit on
continental margin
sion
sio
sio
Ocean
Oceanic crust
Continental crust
Moho level
Lithosphere
Asthenosphere
Asthenosphere rebounds
under eroding mountains
phe
odin
phe
odi
(b)
Ocean
Continental crust
Oceanic crust
Moho level
Asthenosphere
subsides under
continental margins
due to weight
of sediments
Lithosphere
Asthenosphere
Asthenosphere almost level
under eroded mountains
(c)
Figure 12.3 Isostatic adjustment. (a) Continental crust is thickest where mountain ranges occur. Given the extreme weight of these
locations, the underlying asthenosphere subsides relative to the area beneath the oceanic crust. (b) As mountains weather, the weight of
the landmass decreases, allowing isostatic rebound of the asthenosphere. At the same time, the asthenosphere beneath the continental
margin begins to depress due to the increased weight of the freshly deposited sediments eroded from the continental interior. (c) As the
continent weathers further, the isostatic rebound of the underlying asthenosphere continues. At the same time, the asthenosphere is further
depressed due to the increased weight of margin sediments.
peoples' lives. The asthenosphere is the lowermost of
these layers and extends to a depth of 250 km (155 mi).
The upper part of the asthenosphere forms the litho-
sphere, which contains the Earth's crust.
4.
The Earth's crust is divided into oceanic and continental
crusts. The oceanic crust is composed mostly of dense,
fine-grained basalt, whereas continental crust consists
mostly of coarse-grained granite.
 
Search WWH ::




Custom Search