Geology Reference
In-Depth Information
4
LARGE-SCALE TECTONIC AND
STRUCTURAL LANDFORMS
Deep-seated geological processes and structures stamp their mark on many large landforms. This chapter looks at:
Plate tectonic, diastrophic, and volcanic and plutonic processes
How tectonic plates bear characteristic large-scale landforms at their active and passive margins and in their
interiors
The connections between tectonic geomorphology and large-scale landforms
Splitting a continent
On 14 September 2005, a 4.7-magnitude earthquake in Dabbahu, 400 km north-east of Addis Ababa, Ethiopia, was
followed by moderate tremors. Between 14 September and 4 October 2005, 163 earthquakes greater than magnitude
3.9 and a small volcanic eruption (on 26 September) occurred along the 60-km Dabbahu segment of the Afar rift
(Figure 4.1). This volcano-seismic event marked a sudden sundering of the African and Arabian tectonic plates
(Wright
et al
. 2006). It created an 8-m rift in just three weeks (Plate 4.1), a thin column of which filled up with
magma forming a dyke between 2 and 9 km deep, with 2.5 km
3
of magma injection. The sudden rifting added to
the long-term split that is currently tearing the north-east of Ethiopia and Eritrea from the rest of Africa and could
eventually create a huge new sea. The earth movements of September 2005 are a small step in the creation of a new
whole ocean that will take million of years to complete. However, this event is unparalleled in geological investigation
and it has given geologists a rare opportunity to monitor the rupture process first-hand.
