Between a Rock and a Hard Place

InSAR

What’s up in Bolivia?

James Hickey is a PhD student in the School of Earth Sciences at the University of Bristol. A geophysicist and volcanologist by trade, his PhD project is focussed on attempting to place constraints on volcanic unrest using integrated geodetic modelling.

To many, Bolivia is just an unassuming landlocked country in South America, perhaps most famous for its coca tea obsession and ‘gap yah’ alpaca wool sweaters. But to a number of enthused volcanologists it is a near-perfect playground. In the southwest of the country, sitting at 6008 m above sea level (ASL), Uturuncu volcano is inflating, and inflating over an unprecedented scale.

Uturuncu Volcano in the background with a gravimeter and campaign GPS setup in front. Image credit: James Hickey.

Uturuncu Volcano in the background with a gravimeter and campaign GPS setup in front. Image credit: James Hickey.

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Science Snap (9): Sentinel-1

Sentinel-1 satellite to be launched in Spring 2014. Copyright: ESA/ATG Medialab

Sentinel-1 satellite to be launched in Spring 2014. Copyright: ESA/ATG Medialab

 

This isn’t strictly a photograph but an artist’s impression of a new satellite launching soon that will hopefully change the pace and advancement of a satellite remote sensing technique I use in my PhD, InSAR. Sentinel-1 will be the first of five European Space Agency (ESA) satellites to be launched as part of Europe’s Global Monitoring for Environment and Security (GMES) ‘Copernicus’ programme. This multi-billion (euro) project “will be engaged in wide range of land and ocean surveillance tasks, such as oil-spill monitoring and earthquake hazard assessment”.

Sentinel-1 will be a polar-orbiting radar satellite that can collect data day-and-night, in any weather condition, and will be ready for launch in spring 2014. The launch of this satellite is exciting for scientists as it will see the continuation of Synthetic Aperture Radar (SAR) data collection that was, until recently, collected by the ENVISAT satellite.

Aside from InSAR, the ESA website highlights other uses of SAR imagery including “monitoring Arctic sea-ice, routine sea-ice mapping, surveillance of the marine environment, including oil-spill monitoring and ship detection for maritime security, monitoring land-surface for motion risks, mapping for forest, water and soil management and mapping to support humanitarian aid and crisis situations”.

Kenya’s rumbling volcanoes

In the Kenyan Rift, where volcanoes are numerous, satellite observations have identified ground deformation at a number of volcanic centers. Radar images reveal that shallow magma systems may be active under at least four of the volcanoes in Kenya, but whether the signals are driven by an influx of new magma remains to be determined. Here I explain  the background and basis of my PhD project, and why we’re interested in Kenyan volcanoes to start with.

Evidence for extensive magmatism is rife throughout the Rift Valley. Effusive lava flows cover the rift floor, and ashfall deposits from explosive eruptions cover great distances. Yet, in Kenya, no eruptions have been recorded in human history. Consequently, no monitoring infrastructure is in place and the fifteen Quaternary volcanoes along the rift axis remain understudied.

InSAR image of Longonot volcano showing uplift Credit: Juliet Biggs

InSAR image of Longonot volcano showing uplift Credit: Juliet Biggs

Using a satellite technique called InSAR (Interfermoetric synthetic aperture radar), scientists can use satellite imagery to precisely detect changes in the Earth’s surface. The movement of magma beneath a volcano can result in it bulging and inflating, indicating that magma may be making its way to the surface in order to erupt. Whilst not every inflating volcano may result in a eruption, it is indicative that something is churning under the Earth’s surface.

InSAR observations have recently revealed periods of ground deformation at four Kenyan volcanoes. Between 1997 and 2008, uplift of 9 cm and 21 cm occurred at Longonot and Paka (figure 1), whilst subsidence was seen at Menengai and Suswa of 3 cm and 4.6 cm (Biggs et al., 2009).

This discovery implies that the magmatic systems under these Kenyan volcanoes may be more active than previously thought. Current research now focuses on understanding the dynamics of these volcanoes, and more specifically, teasing apart the mechanisms of the observed ground deformation.

SPOT5 image of Longonot volcano, Kenya

SPOT5 image of Longonot volcano, Kenya. Credit: Elspeth Robertson

Of the four volcanoes that have shown volcanic ground displacements, Longonot poses a large risk to the Kenyan population and its economic exports, especially nearby exporting flower farms. Longonot is a small stratovolcano 70 km northwest from Nairobi and just south of Lake Naivasha. The volcanic flanks are piled high with viscous lava flows and the surrounding area is covered in an ashfall deposit, the Longonot Ash, dating back to 3200 years. The explosive eruption that produced this ashfall was likely concurrent with the formation of the circular pit caldera seen today (figures 2 and 3). Distinctive black lava flows, clearly overlying the ash deposits, mark the Longonot’s last eruptive activity. Whilst the lava flows haven’t been dated, they’re estimated be less than 1000 years old.

The Longonot Ash likely resulted from an explosive Plinian eruption (Pyle, 1999) producing a plume that distributed ash beyond the neighbouring volcano, Olkaria. Studies on Longonot so far concentrated on the geochemistry of the lavas, and very little is known about the physical emplacement processes and the physical detail of the recent eruptives, both ashfall and lavas.

Understanding the physical volcanology of ashfall and effusive deposits provides a constraint on the magmatic conditions that can lead to an eruption. To investigate this, a well established approach is to use a combination of remote sensing mapping techniques and fieldwork. The optical imagery over Kenya is spectacular, largely due to the dry climate and lack of cloud cover, and is perfect for a detailed geological study. Analysis using optical imagery is, as always, bolstered by ground-truthing and fieldwork provides the opportunity to sample the rocks for geochemical analysis in the lab.

As research continues, tying together these approaches will lead to a greater understanding of the underlying processes of these mysterious volcanic bulging and deflating events.

 

This blog post is an adapted version originally written for the Geological Remote Sensing Group newsletter.

References:

Biggs, J., Anthony, E.Y., Ebinger, C. Multiple inflation and deflation events at Kenyan volcanoes, East African Rift. Geology. 2009.

Pyle, D. 1999. Widely dispersed Quaternary tephra in Africa. Global and Planetary Change, 21, 95-112.

Science snaps (1): Africa’s Ups and Downs

Each week we’ll be featuring our favourite ‘science snaps’ on the blog. These posts will showcase images, photos, films and figures that we encounter on a day-to-day basis, as well as things which we simply think are cool and should be gawped at. All of the contributors to Between a Rock work in various veins of volcanology and so the upcoming images will be quite diverse…

Without further ado, and trying to keep to the snappy title, I’m starting off with a 3D animation flying through the East Africa Rift zooming into areas of volcano and earthquake deformation observed from satellite imagery.

The animation by the European Space Agency is titled “Africa’s ups and downs” and predominately features the work of Juliet Biggs here in the Bristol School of Earth Sciences.

Watch the video and have a look at the webpage that explains the science of the techniques used. Credits: Planetary Visions/NERC-COMET/JAXA/ESA