Will Hutchison
Uncovering the eruptive history of
volcanoes in the Main Ethiopian Rift
For geologists Ethiopia is
perhaps one of the most
spectacular places on earth.
There it is possible to witness
the slow and gradual tearing
apart of the continental crust
and the birth of a new ocean.
Over the last five years, Oxford
geologists have been part
of a large UK NERC funded
consortium project to study
rifting processes in the remote
inhospitable region of Afar.
Using the latest geophysical
Installing GPS stations
and geochemical techniques,
the researchers braved
surface temperatures in excess of 50°C. Several
field seasons and volcanic eruptions later, they have
provided a wealth of information concerning rifting
processes (uncovering, for example, the way in which
dykes are emplaced beneath these rift zones, and the
depths which magma is pooling in the Ethiopian crust).
Following the success of the Afar Consortium
project we are now turning to investigate the lesser
understood area, to the south-west of the Afar
Depression: the Main Ethiopian Rift, a narrow rift
valley 300km long and 80km wide. This area is very
different from Afar; the climate is far less extreme,
The view from inside Alutu caldera
thus a huge population has
developed around the lakes
and volcanoes of the rift
valley floor. The age and
eruptive histories of the Main
Ethiopian Rift volcanoes
are virtually unknown and
not one has any dedicated
monitoring equipment. There
is an intriguing paradox with
these volcanoes: all show
clear signs of large eruptions
in the past (thick deposits of
pumice and ash, as well as
large calderas) but there have
been few significant eruptions
noted in historical records. So are these volcanoes
simply remnants of a more ancient and active past or
are they dormant, poised for future eruption?
While we cannot yet be certain of this, recent work by
Dr. Juliet Biggs (previously Oxford, now Bristol) using
satellite radar (InSAR) to monitor surface deformation
has shown that these volcanoes are very much active.
She found that several volcanoes, located in the Main
Ethiopian Rift, are actively deforming, the most notable
being Alutu volcano. Alutu showed two large uplift
episodes in 2004 (15cm) and 2008 (10cm) which
took place over a relatively short timescale. This work
confirms that these are indeed active volcanoes and
poses several fundamental questions: how active
have these volcanoes been in the past? What causes
this deformation? Can we make any predictions as to
the future activity?
Our current work addresses these issues. We are
carrying out a detailed multi-disciplinary study of Alutu
volcano which, we hope, will form one of the first
detailed case studies of a Main Ethiopian Rift volcano.
Similarly to the groups working in Afar, we are
employing various different methods (including GPS
deployment, gas monitoring, satellite remote sensing
and traditional geological mapping) to establish the
current activity of Alutu and to build up a detailed
eruptive history of the complex. Our initial fieldwork,
conducted in January and May 2012, showed that
Alutu has been the site of numerous eruptions in
the past, of a variety of styles. These included thick
explosion deposits of pumice and pyroclastic debris,
as well as viscous, oozing lava, formed of dark glassy
obsidian. Across the volcano there are several sites
at which strong fumarolic activity takes place. This
demonstrates that the volcano is very much alive
beneath the surface.
Crucially, there are several thousand people living on
the volcano and many more in the surrounding towns
and villages. With so little previous work on Alutu,
our motivation is to understand the volcanic hazards
which are posed to this local population, and only by
establishing a detailed history of past eruptions, and
deploying a monitoring network, can we achieve this.
Credit: ESA
InSAR image of Alutu.