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How do magmatic mush zones deform?

Dr Susanna Ebmeier (SEE), Dr Dan Morgan (SEE) and Prof Andy Hooper (SEE)

Contact email: s.k.ebmeier@leeds.ac.uk

Magma spends the majority of its time stored in the Earth’s crust in mush zones  - complex regions of non-eruptible crystal-rich magma thought to be interspersed with lenses of melt and volatiles [1].  Evidence for such mush zones comes from the crystal cargo of erupted rocks, laboratory experiments and modelling.  We know that melt and volatile phases separate out from, and move through, crystal-rich mushes [2].   Both thermal modelling [3] and diffusion chronometry [4] have also demonstrated that reservoirs of eruptible magma assemble relatively rapidly.  Detecting this happening in real time would have great and immediate benefit for volcanic monitoring and assessment of volcanic hazard. 

Changes within a mush zone are challenging to detect while they are happening, i.e. with geophysical methods. It is generally assumed that many processes, including melt migration and phase changes, can take place in a mush zone without causing any deformation at the Earth’s surface.  However, volcanic deformation signals are prevalent [5], including at mature volcanoes and calderas where we would explain magma storage to involve mush zones.  This studentship will address the question of why these deformation signals occur, using a range of observational and modelling approaches. 

This will involve several strands of investigation:

  • Assessing the volcano geodesy archive (predominantly from Interferometric Synthetic Aperture Radar, InSAR, measurements) for examples of deformation signals that are likely to have originated in mush zones.   Data for interesting cases will be reprocessed at full resolution and using the latest approaches to atmospheric corrections to best characterise the deformation signal.  The student will identify a case study volcano with deformation that can be confidently associated to a mush zone, and where melt and crystal mush texture and composition have been well constrained, and which is therefore suitable for modelling experiments. 
  • Using modelling for the identified test case to establish under which circumstances processes expected in a mush zone, (e.g., melt segregation due to compaction or melt migration in response to a pressure gradient) will cause deformation.  This will be achieved using a combination of thermodynamic modelling to predict the physical properties of melt and mush at different temperatures, and analytical solutions for elastic and viscoelastic deformation.
  • Evaluation of whether the deformation identified is consistent with a localised body of melt or with a more distributed change within a mush. Establish what impact the presence of a mush zone makes to estimations of melt (and ultimately eruptible magma) volume.

Objectives

The student will work with scientists in Leeds to: 

  • Build a comprehensive dataset of geodetic signals that at a best guess from setting and past eruptive products should be interpreted in terms of a mush zone.
  • For a particular test case, make an assessment of the probability of various mechanisms of melt segregation and migration causing deformation and ascertain the range of volume changes that deformation could represent. 

Potential for high impact outcome

Detecting the accumulation of magma at active volcanoes requires models that can connect processes in a mush zone to observables at the Earth’s surface.  This is a challenging problem, and by testing and assessing models for a range of processes at a particular system, this project will make an advance to the way that widely used geodetic data are interpreted that will potentially be useful to any scientists interpreting volcanic monitoring data.   

Training

The student will work under the supervision of Dr Susanna Ebmeier in the Institute of Geophysics and Tectonics volcanology group.   The student will be trained in processing and analysing SAR deformation data, as well as modelling deformation using elastic and viscoelastic analytical solutions.   The student will be encouraged to expand their scientific horizons by participating in training programmes supported by international volcanological and geophysics networks such as IAVCEI and UNAVCO. The successful PhD student will have access to a broad spectrum of training workshops put on by the Faculty of the Environment at Leeds (http://www.emeskillstraining.leeds.ac.uk/).

Student profile

The student should have an interest volcanology and be enthusiastic about understanding and using analytical and numerical modelling approaches.  The student should have a background in a quantitative science with some experience and interest in scientific computing. 

References

  1. Cashman et al., (2017). Science, 355(6331)
  2. Hartung et al., (2017). J. Petrology, 58(4), 763-788.
  3. Annen et al., (2005). J. Petrology., 47(3), 505-539.
  4. Cooper et al., (2017). Ear. Plan. Sci. Lett., 473,1-13.
  5. Biggs, Ebmeier, et al., (2014). Nat. Comm., 5.

Related undergraduate subjects:

  • Applied mathematics
  • Chemistry
  • Computer science
  • Computing
  • Earth science
  • Earth system science
  • Geological science
  • Geology
  • Geophysical science
  • Geophysics
  • Geoscience
  • Mathematics
  • Natural sciences
  • Physical geography
  • Physical science
  • Physics
  • Remote sensing