Short-period deformation at a lava dome volcano

Lead Research Organisation: University of Reading
Department Name: Meteorology


At erupting volcanoes, just before magma, or molten rock, arrives at the surface to produce lava and ash, it can become much more viscous and reluctant to flow. This change in character of the magma in turn affects a number of other processes - high pressures build, gas flows change and the rate of flow of the magma itself becomes variable. Sometimes these changes vary systematically every few hours to produce a periodic behaviour. Being able to measure such periodic behaviour is very useful to scientists in volcano observatories for two reasons. Firstly, certain times in the period are much more prone to explosions and hazardous flows, and so being able to forecast their occurrences is useful. Secondly, by observing how a variety of phenomena change during each cycle allows the conditions that give rise to the periodic flow to be understood. This in turn allows the longer-term behaviour of the volcano to be better anticipated, with benefits to people affected. In this project we will improve our understanding such behaviour at Soufriere Hills Volcano, Montserrat. This type of periodic behaviour is probably common at the more dangerous type of volcano with magma rich in silica. However, it is very difficult to observe and as a consequence not well understood. This is because some of the signals associated with it are restricted to near the vent of volcano and are difficult to measure. One place where such periodic signals were measured is Soufriere Hills. Over an interval of a few months in early 1997, tiltmeters that measure the inclination of the ground surface, recorded a remarkable series of cycles of ground motion up and down with a period of about 9 hours. Unfortunately, the tiltmeters were destroyed by the volcano and the location was subsequently too dangerous to re-install new ones. We plan to bring a new technology to bear on this problem in a 2-year project based at the University of Reading and applied at the Montserrat Volcano Observatory. Rather than measure the ground movement using an instrument buried in the ground we will do so from a safe distance using radar interferometry. From a few kilometres away we will measure the outward and inward movement of the ground around the lava dome growing within the crater at Soufriere Hill. We expect the cycle to be measured over a few hours and to an accuracy of a few millimetres for a signal ten times as large. A portable, ground-based radar interferometer has been developed for this type of task, and we will be the first to use it on a volcano like this. Because the instrument gives an image of the ground displacement rather than a point reading it will be able to measure the spatial pattern of motion, by making measurements from different viewpoints. This will enable the new measurements to test a hypothesis that the conduit feeding the magma to the surface below Soufriere Hills Volcano has a shape like a vertical cylinder joined onto a fissure below depths of about one kilometre. The technology of the measurements of earthquakes, gas and wider deformation of the whole island routinely made by the Montserrat Volcano Observatory has advanced greatly since 1997, particularly the frequency of measurements. We will use these frequent (very hour and less) measurements of the cycle to compare with a computer simulation of the magma-filled conduit. This will help us to understand better how the conduit behaves and how it might behave in the future.


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Costa A (2012) Cyclic extrusion of a lava dome based on a stick-slip mechanism in Earth and Planetary Science Letters

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Odbert H (2014) Chapter 2 Cyclic phenomena at the Soufrière Hills Volcano, Montserrat in Geological Society, London, Memoirs

Description The way in which the top of a volcano deforms over periods of hours to days can potentially provide us with information on the forces within the rising magma column and help determine whether the volcano is likely to erupt explosively. We have developed and tested analytical models of the magma movement and shown how the forces operating there combine to produces cycles of magma flow and deformation
Exploitation Route Whilst the lack of a deformation signal prevented us from testing the magma flow models, the instrument we used - a ground based radar interferometer was an excellent detector of water vapour in the atmosphere. So we have used the data collected to better understand the water vapour profile around the volcano. This can help mitigate this effect in the technique of satellite-based radar interferometry.
Sectors Aerospace, Defence and Marine,Environment

Description Our magma conduit modelling is being used by the wider volcano logical community. The radar measurements are only just being worked up for publication and so it is still too early to judge how influential they will be.
First Year Of Impact 2012
Sector Environment
Impact Types Societal

Description Risk Assessment for volcanic activity at Montserrat
Geographic Reach National 
Policy Influence Type Participation in a guidance/advisory committee
Impact As chairman of the FCO's Scientific Advisory Committee for volcanic activity on Montserrat during the second half (2003-2014) of the 1995-2010 eruption of Soufriere Hills Montserrat I help create and deliver a consistent praxis of risk assessment to the governments of Montserrat and the UK (via the FCO) (see doi: 10.1144/M39.24).
Description Working with Montserrat Volcano observatory scientists 
Organisation Montserrat Volcano Observatory
Country Montserrat 
Sector Academic/University 
PI Contribution In October 2012 and August 2013 we visited Montserrat Volcano Observatory to liaise with staff on GPS data and to make joint measurements with the GPRI2 radar interferometer. Successful outcome, but unfortunately the volcano was not erupting at the time. We have shown our colleagues the potential of ground-based radar interferometry
Collaborator Contribution Our joint work on the use of the interferometry data for water vapour analysis is helped by the processing of signals from the observatory's GPS network.
Impact We are currently working on the first collaborative paper with MVO scientists.
Start Year 2012