Using Satellite Imagery to Identify Active Magma Systems in East Africa’s Rift Valley
Surface deformation of four active volcanoes captured on InSAR underscore possibility for human hazard, potential of geothermal resources
A team from the University of Miami, University of El Paso and University of Rochester have employed Interferometric Synthetic Aperture Radar (InSAR) images compiled over a decade to study volcanic activity in the African Rift. The study, published in the November issue of Geology, studies the section of the rift in Kenya.
“The Kenyan Rift volcanoes are part of a larger Great Rift Valley complex that extends all the way from Mozambique to Djibouti; their presence in East Africa attests to the presence of magma reservoirs within the Earth’s crust,” said Lead Author Dr. Juliet Biggs, Rosenstiel Postdoctoral Fellow at the University of Miami. “Our study detected signs of activity in only four of the 11 volcanoes in the area — Suswa, Menengai, Longonot and Paka — all within the borders of Kenya.”
Small surface displacements, which are not visible to the naked eye, were captured using InSAR, a sophisticated satellite-based radar technique. Using images from European Space Agency satellites ERS and Envisat, the team was able to detect the smallest ((<1 cm) of surface displacements at a very high resolution. From 1997 – 2000 they discovered that the volcanoes at Suswa and Menengai subsided 2 – 5 cm, and between 2004 and 2006 the Longonot volcano experienced uplift of ~9 cm. However, the most dramatic uplift unfolded at Paka, which had uplift of ~21 cm during a nine month period in 2006-2007. This pulse of activity was preceded by transient uplift and subsidence at a second source, associated with the magma flow through the complex underground plumbing system. Overall the events were short in duration and episodic rather than continuous, which means discrete pulses of magma were arriving at the crust, similar to a stop valve that is being turned on and off intermittently.
“The fact that these areas are so close to a major metropolitan area pose a challenge in terms of a large volcanic or seismic event” says co-author Cindy Ebinger. Suswa, Menengai and Longonot are all located in densely populated areas within 100 km of Nairoibi.
The study also provides insight as to the geothermal potential of the region. Kenya was the first African country to build geothermal energy plants to generate this renewable, environmentally friendly alternative to coal and oil. The impact of harnessing such a resource could provide an important economic engine for the region.
Geothermal energy is generated by drilling deep holes into the Earth’s crust, pumping cold water through one end so by the time it resurfaces it is steam, which is then used to fuel a turbine, which in turn drives a generator, and creates power.
“This study demonstrates the potential for using InSAR to measure active magmatic and tectonic phenomena in Africa, allowing us to watch the processes by which continents break apart” says lead author Juliet Biggs, who has just begun a 2-year project at the Univeristy of Oxford, funded by the European Space Agency, to map the pattern of volcanic activity, dike intrusion and active faulting along the whole of the East African Rift.
[Source: Rosenstiel School of Marine and Atmospheric Science, University of Miami press release]