Planet Earth and Earth systems - Physical Processes in Earth and Environmental Sciences - page 6

Fig. 1.7 Grand Canyon, Arizona: “Mother of all canyons.”

Fig. 1.9 San Andreas Fault, California.

California, cuts the landscape (Fig. 1.9). Its eroded and
gullied scarp is witness to periodic catastrophic ruptures of
the Earth's lithosphere in response to long-term stress
build up as the North American plate (right) slides relent-
lessly past a subportion of the Pacific plate (left). The
surface displacement, fault trace length, and orientation of
the fault provide information concerning the tectonic
stresses responsible, while the energy release as seismic
waves during earthquakes gives insight into the Earth's
interior structure.

1.3.5 Volcanic eruption in island arc

Fig. 1.8 Flash flood showing upstream-migrating waves typical of
supercritical flow. Arizona, August 1982. Flow top to bottom.

Molten magma at 600-1,200 C is produced as lithos-

pheric plates separate at mid-ocean ridges or at island arcs
inboard of subduction zones where plate is returned to
middle Earth. The magma reaches Earth's surface and
interacts with the hydrosphere and atmosphere at 20

flow. Downstream coalescence of overland flow into newly
eroded rill channels and then into larger tributary channels
concentrated the runoff as a flash flood. The flood built up
far from the source of the rainfall and took a community
of campers by surprise, though fortunately there was no
lasting damage in this case.

C.
Outgassing, quiescent lava extrusion, local explosive fire
fountains, upward-directed explosions of tephra, growth
and collapse of rock lava domes, and lateral flow of gas
mixed with incandescent scoriae (pyroclastic flows,
Fig. 1.10) are all alternative eruption scenarios: the exact
outcome is dependent upon the type of magma and its
near-surface interaction. Aerosols and fine ash from Plinian
explosive eruptions may enter the top atmospheric boundary
layer where they reflect shortwave solar energy back into
space, causing temporary global cooling over a year or so.

1.3.4 Earthquake fault along plate boundary

The linear surface trace of perhaps the world's most
famous active fault, the San Andreas fault of southern