Investigating Pulses of Ground Deformation at Volcanoes in the Main Ethiopian Rift
Hutchison, William1; Biggs, Juliet2; Mather, Tamsin1; Pyle, David1; Yirgu, Gezahegn3
1University of Oxford, UNITED KINGDOM; 2University of Bristol, UNITED KINGDOM; 3University of Addis Ababa, ETHIOPIA

The Main Ethiopian Rift is lined by a series of regularly spaced silicic volcanic complexes, typically 10-20km in diameter. While most of these complexes show signs of large caldera forming eruptions in the recent past, little is known of how active these volcanoes are currently and what the frequency and magnitude of past eruptions has been. In a recent report by the Global Facility for Disaster Risk Reduction (GFDRR) of the World Bank they outlined the importance of developing our understanding of these volcanoes and identified several of these complexes as "high-risk", based on quantifying hazard potential and population exposure.

In the absence of detailed historical records we use satellite-based interferometric synthetic aperture radar (InSAR) observations to investigate both past and present volcanic activity. InSAR observations (ENVISAT) demonstrate that significant deformation has been occurring at four volcanic edifices in the Main Ethiopian Rift (Alutu, Corbetti, Bora and Haledebi) from 1993-2010 [Biggs et al., 2011]. The largest displacements are at Alutu volcano, which has undergone large pulses of uplift in 2004 (15cm) and 2008 (10cm) separated by gradual subsidence.

While the deformation pulses are almost certainly due to fluid movement beneath these volcanoes it is unclear whether the source is magmatic or hydrothermal in origin and at present our best-fitting source depth models are consistent with the boundary between these two systems. Our current work focuses on better constraining the exact source of the deformation and to develop our understanding of its dynamics and timescale response. To do this we are combining new ALOS and ENVISAT Wide Swath data with current InSAR observations to increase the temporal resolution of our deformation time-series. In addition, we are comparing the InSAR results with a variety of geophysical and geochemical techniques including seismicity, magnetotellurics and diffuse CO2 degassing, which we began collecting in January 2012, to begin probing the deeper structure of the volcano.

This detailed multi-parameter field and remote sensing based approach will offer some of the first detailed constraints on the current activity of volcanoes in Main Ethiopian Rift. Through these new data we hope to contribute to the assessment of volcanic hazard at Alutu, and more generally, to expand our knowledge of the role these silicic volcanic centres play in continental rifting processes.