Plate Tectonics: A Unifying Theory - The Changing Earth: Exploring Geology and Evolution - page 44

◗

Figure 2.16 History of a Divergent Plate Boundary

Rising magma beneath a continent pushes
the crust up, producing numerous fractures,
faults, rift valleys, and volcanic activity.

Volcanic activity a

Magma

Continental crust

As the crust is stretched and thinned, rift valleys develop and lava
fl ows onto the valley fl oors, such as seen today in the East African
Rift Valley.

Rift valley b

Coastal mountain
range

Continued spreading further separates the continent until
it splits apart and a narrow seaway develops. The Red Sea,
which separates the Arabian Peninsula from Africa, is a good
example of this stage of development.

Narrow fault-bounded sea c

As spreading continues, an oceanic ridge system
forms, and an ocean basin develops and grows.
The Mid-Atlantic Ridge illustrates this stage in a
divergent plate boundary's history.

d

Continental “seaboard”
(coastal mountains gone)

Wide ocean