Department of Geography, Environment and Earth Sciences

Rebecca Williams

Rebecca Williams

Lecturer in Volcanology

Department of Geography, Environment and Earth Sciences

  • Profile
  • Research
  • Publications

Profile

Background

Dr Williams joined the Department in February 2013 from the University of Leicester.

Teaching

  • 16120 : Landforms & Ecosystems 
  • 16272 : Dynamic Planet 
  • 16438 : Volcanoes and Their Hazards

Committee Member of the Volcanic and Magmatic Studies Group.

Research

Research Interests

My main research interests are investigating and understanding explosive volcanism and hazardous volcanic phenomena, particularly pyroclastic density currents and lahars. I am also interested in understanding volcanic systems from source to eruption through interrogating volcanic stratigraphy, geochemistry and mineralogy. I currently have three main research projects:

  • Assessing the mantle plume component of the Louisville Seamount Chain, SW Pacific Ocean
  • Emplacement of radial pyroclastic density currents over irregular topography: the chemically-zoned, low aspect-ratio Green Tuff Ignimbrite, Pantelleria, Italy
  • Modelling lahars using Titan2D for the southern drainage of Volcán Cotopaxi: Impact on the city of Latacunga

Assessing the mantle plume component of the Louisville Seamount Chain, SW Pacific Ocean

Louisville MapOne of the main products from melting of the Earth's interior is basalt. Basalt underlies the ocean basins, forms the bulk of ocean islands, and is found throughout the continents and it is the closest we have to providing a window into the Earth’s mantle. The mantle convects on a range of scales, and comprises several chemical reservoirs. Basalts formed by melting of these reservoirs provide information about the evolution of the Earth's interior.

The Louisville Seamount Trial, recently drilled during IODP Expedition 330, provides an opportunity to test some new ideas on the heterogeneity of these chemical reservoirs in the mantle. Expedition 330 recovered >800 m of rock from 5 seamounts at the older end of the Trail, emplaced during the late Cretaceous. I sailed on this expedition as an igneous petrologist and collected, in collaboration with other shipboard scientists, 100 samples for bulk rock geochemical study and 40 samples for isotopic analysis.

Louisville photo courtesy of Christophe BeierI am currently analysing the samples by mass spectrometry (for Nd and Hf isotopes), and ICP-MS (for high-precision trace element data), and collaborators at the University of Edinburgh are analysing the samples by XRF (for high-precision major element and trace element data). The major and trace element data will enable us to determine (a) depth and extent of melting and, together with the isotope data, (b) the composition of the mantle components sampled by the melt regime. The data will also enable us to determine the relative contribution of distinct mantle source components in the formation of basalts recovered from the Louisville Seamount Trail.

Emplacement of radial pyroclastic density currents over irregular topography: the chemically-zoned, low aspect-ratio Green Tuff Ignimbrite, Pantelleria, Italy

The Green Tuff draping caldera wall successions under Scauri VillageLow aspect-ratio ignimbrites are thought to be emplaced by particularly hazardous, radial, high-velocity pyroclastic density currents from caldera-forming eruptions. Their circular distribution has been inferred to record simultaneous flow in all directions from source, overtopping hills, rather than passively flowing down valleys. This study aimed to understand how such currents behave and evolve during an eruption by mapping out the internal chemical-architecture of a zoned, low-aspect ratio ignimbrite sheet on the island of Pantelleria, Italy. The pristine, welded Green Tuff Formation (aspect ratio >1:1,000) was deposited during the most recent (c. 50 ka) explosive eruption on the island. The extensive flow-The Green Tuff draping near-vertical caldera wall at Bagno dell'Acquaunit is zoned from pantellerite to trachyte, recording changes in the composition of the erupting magma with time. Detailed logging with very close-spaced sampling for chemical (LA ICP-MS, e-probe, SEM and XRF) and petrographic analysis has distinguished an internal chemical stratigraphy that allows the brief history of the sustained current to be divided into successive time-periods. The compositional zones have been mapped around the island enabling the reconstruction of how the footprint of the sustained current shifted during the eruption as the current waxed and then waned. Furthermore, the mapped compositional zones can be used to assess how the current and its resultant deposit encountered and overtopped barriers, such as cone-shaped hills and transverse ridges. This study has revealed that the ignimbrite was not emplaced entirely radially: rather, it flowed into certain sectors before others, and that the leading edge of the current advanced and then retreated, and shifted laterally with time. Deposition was diachronous, and previously proposed lithofacies correlations within the ignimbrite are demonstrated to be incorrect. As the pyroclastic density current encroached upon topographic barriers, it was initially blocked, reflected, or deflected around the lower flanks of the barrier. As the mass-flux of the eruption increased, the current waxed and was progressively able to overtop topographic barriers.

 

Modelling lahars using Titan2D for the southern drainage of Volcán Cotopaxi: Impact on the city of Latacunga

Williams et al., 2008Lahars triggered by mobilization of deposits from volcanic explosions have occurred at Volcán Cotopaxi, Ecuador on the average of once every century over the last two millennia. Lahars from Cotopaxi may flow down three main drainages, impacting a present day population of around 3 million inhabitants. Río Cutuchi, the main drainage to the south of Cotopaxi, headwaters on the flanks of Rumiñahui and Cotopaxi Volcanoes. This river flows southwards through several communities, including the city of Latacunga (population 52,000). Its path is generally parallel to the Pan American highway. Many small scale lahars have followed this drainage, as well as some large scale historical flows, such as the great 1877 debris flow that severely impacted the population along the Río Cutuchi. This study used the Titan2D modelling code to simulate lahars of various volumes that correspond to actual deposits along the Río Cutuchi in the vicinity of Latacunga. The purpose was to investigate the hazard that lahars might present to the current population should Cotopaxi become active again and produce debris flows. The study area is restricted to the region adjacent to Latacunga, where detailed field data are compared with the model results. Simulations used topographic, stratigraphic, and Williams et al., 2008historical inundation data collected in the field in the summer of 2005 to determine probabilistic lahar inundation zones for the debris flows of various sizes. These inundation zones have been analyzed in conjunction with infrastructure data for Latacunga, so that the impact of various scale lahars on the city can be assessed.

This study also involved evaluating Titan2D. This geophysical mass flow model was evaluated by comparing simulated flows with an actual event that occurred in February, 2005 in the Vazcun Valley at Volcán Tungurahua, Ecuador.

Publications

Publications

Williams, R; Branney, M.J.; Barry, T.L.; (In prep). Waxing and waning geophysical density currents: temporal changes in run-out distance revealed by chemical mapping. Intended for submission to Nature.

Williams, R.; Branney, M.J.; Barry, T.L.; Norry, M.; (In prep). Emplacement of radial pyroclastic density currents over irregular topography: the chemically-zoned, low aspect-ratio Green Tuff ignimbrite, Pantelleria, Italy. Intended for submission to (e.g.) Philisophical Transations of the Royal Society of London

Williams, R.; Branney, M.J.; (In prep). The physical volcanology of the Green Tuff Formation: an integrated lithofacies and geochemical stratigraphy approach. Intended for submission to the Bulletin of Volcanology.

Koppers,A.P. ; Yamazaki, T.; Geldmacher, J.; Gee, J.S.; Pressling, N.; Hoshi, H.; Anderson, L.; Beier, C.; Buchs, D. M.; Chen, L-H.; Cohen, B. E.; Deschamps, F.; Dorais, M. J.; Ebuna, D.; Ehmann, S.; Fitton, J. G.; Fulton, P. M.; Ganbat, E.; Hamelin, C.; Hanyu, T.; Kalnins, L.; Kell, J.; Machida, S.; Mahoney, J. J.; Moriya, K.; Nichols, A. R. L.; Rausch, S.; Sano, S-i.; Sylvan, J. B.; & Williams, R. 2013. Limited latitudinal mantle plume motion for the Louisville hotspot. Nature Geoscience 6, 76 doi:10.1038/ngeo1677

Koppers, A.A.P., Yamazaki, T., Geldmacher, J., and the Expedition 330 Scientists; 2012. Volume 330 Expedition Reports – Louisville Seamount Trail. Proc. IODP, 330: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.330.2012

Fitton, J.G.; Williams, R.; Anderson, L.; Kalnins, L.; Pressling, N.; 2011. Expedition 330: The Louisville Seamount Chain. UKIODP Newsletter 36, August 2011.

Expedition 330 Scientists, (2011). Louisville Seamount Trail: implications for geodynamic mantle flow models and the geochemical evolution of primary hotspots. IODP Preliminary Report 330. doi:10.2204/iodp.pr.330.2011.

Williams, R., Stinton, A.J., Sheridan, M.F., 2008. Evaluation of the Titan2D Two-Phase Flow Model Using an Actual Event: Case study of the 2005 Vazcún Valley Lahar. Journal of Volcanology and Geothermal Research. 177(4): 760-766.

 

Conference Presentations

Fitton G., Williams R., & Expedition 330 Scientists, 2012. Temporal variation in basalt composition in the Louisville seamount trail: some preliminary results from IODP Expedition 330. VMSG Meeting, Durham, 4th-6th January 2012.

Williams R., Branney M.J., Barry T.L., Norry, M., 2010 Emplacement of energetic density currents over topographic barriers: constraints from a chemically-zoned, topography-draping, low aspect-ratio ignimbrite on Pantelleria, Italy. Geophysical Research Abstracts, Vol. 12, EGU2010-10170, 2010, EGU General Assembly, Vienna, May 2010.

Williams R., Branney M.J., Barry T.L., 2010. Emplacement of energetic density currents over topographic barriers: constraints from a chemically-zoned, topography-draping, low aspect-ratio ignimbrite on Pantelleria, Italy. VMSG Meeting, Glasgow, 4th-6th January 2010

Jordan, N.J., Williams R., Branney M.J., Norry M., 2010. Evolution of an emergent explosive peralkaline volcano: caldera-collapse eruptions of Pantelleria, Straits of Sicily. VMSG Meeting, Glasgow, 4th-6th January 2010.

Williams R., Branney M.J., Norry M., 2009. Emplacement of radial density currents: evidence for shifting flow-paths from chemical mapping of a low-aspect ratio ignimbrite. VMSG Meeting, Bournemouth, 4-6th January 2009.

Williams R., Branney M.J., Barry T.L., 2008. Behaviour of energetic density currents at topographic barriers: evidence from chemical time-lines in a zoned, low-aspect ratio ignimbrite. IAVCEI General Assembley, Iceland, 17-22nd August 2008

Williams R., Branney M.J., 2008. Sustained density currents: how do they change with time? VMSG Meeting, Dublin, 4-5th January 2008.

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