Geoscience Reference
In-Depth Information
Figure 18.6. Main Ethiopian Rift, showing Quaternary lakes and volcanoes. (After
Williams et al.,
2004
.)
sometimes termed the Afar Triple Junction because it is located at the intersection of
the Red Sea, the Gulf of Aden and the Main Ethiopian Rift, is widening at a mean
rate of about 0.5 cm/year and is also subsiding but at a much slower rate (Adamson
et al.,
1993
). Miocene lake sediments and somewhat enigmaticMiocene granites occur
within the Afar (Tiercelin,
1981
; Adamson andWilliams,
1987
), but the most abundant
rocks are basalts and occasional volcanoes, including the spectacular Erta'Ale volcano
with its live lava lake. Pliocene and younger river and lake sediments contain a wealth
of vertebrate fossils, including those of the hominids described in
Chapter 17
.
Rifting began in the Main Ethiopian Rift (MER) around 10 Ma ago, preceded by
initial downwarping at around 15 Ma. Opening up of the 10-20 km wide Wonji Fault
Belt, a zone of closely spaced, normal faults and fissures arranged
en echelon
within
the 80 km wide MER (
Figure 18.6
), probably began about 1.6 Ma ago, and a major
impulse of tectonic and volcanic activity has taken place within the last 0.25 Ma, after
which the present MER lakes came into being. The current rate of widening of the
MER determined from plate tectonic modelling amounts to about 0.5 cm/year, but
