Englacial indicators of surge dynamics: monitoring the evolution of surge-type glaciers with seismic email@example.com
Understanding the stability of glacierised regions in a warming climate is a key research focus, given the serious implications for global sea-level rise and water resources. Predictive models suggest that runaway ice sheet collapse can occur under certain hydrological conditions, if water enters the subglacial system on a retrograde basal slope (e.g. Siegert et al., 2016). Models then predict that the resulting set of feedbacks quickly promotes the rapid mass-loss from the ice stream. This switch from a stable to an unstable ice sheet, and the interplay between stability and basal hydrology, parallels the onset of ‘surge’ behaviour in small outlet glaciers. As such, ‘surge-type’ glaciers can provide a useful analogue for investigating the controls on the stability of more significant ice streams (Ingólffson et al., 2016).
A surge-type glacier undergoes dramatic, cyclical, fluctuations in its flow speed and geometry (Figure 1). A surging glacier can undergo several years of rapid frontal advance (e.g., Quincey et al., 2015), but then abruptly enter a quiescent phase of stagnation that may last for hundreds of years. Very few (1%) glaciers appear to surge (Jiskoot et al., 1998), but their uneven distribution around the world suggests that local – rather than global – environmental mechanisms trigger the onset of the surge phase. However, such triggers and their role in initiating and terminating surges are poorly understood (Rea and Evans, 2011) and numerous non-exclusive mechanisms have been proposed – e.g., switches in the distribution of subglacial hydrology (Bjornsson, 1998) and an evolving englacial thermal regime (Fowler et al., 2001).
Figure 1. Schematic evolution of a surge-type glacier, through phases of quiescence (upper), surge (middle) and termination (lower), based on the surge model of Murray et al. (2000). Mass accumulates up-glacier during the quiescent phase, above water-saturated (‘warm’) basal ice, and advances rapidly during the surge. The surge terminates as basal water encounters, and is evacuated through, permeable basal sediment.
Geophysical methods have been usefully applied to characterise the physical properties of glaciers and their subglacial environment. The seismic reflectivity of the glacier bed has been used to diagnose the presence of subglacial water (Booth et al., 2012), whereas the energy loss of a seismic wavelet can be used as a proxy for englacial temperature (Peters et al., 2012). By monitoring the spatial and/or temporal distribution of the properties of a surge-type glacier, geophysics can help constrain the specific triggers of a surge initiation and termination. Comparing these properties to those from ice streams (e.g., Harrington et al., 2015) will provide insight into the suitability of the surge-type glacier as a proxy for a larger ice mass, as well as shedding light on the controls of glacier dynamic instability, one of the major outstanding questions in glaciological research.
In this project, you will work with leading scientists at the University of Leeds to quantify the physical properties and surge characteristics of accessible surge-type glaciers in Europe. Campaigns of geophysical acquisition, primarily (but not limited to) seismic, will be performed, on the surge-type outlet glaciers of Iceland’s Vatnajökull ice cap. At least 10 Vatnajökull outlets are classified as surge-type, with surge events recorded for at least the last 100 years (Ingólffson et al., 2016; Figure 2). Suitable sites will be determined using InSAR measurements of surface deformation, to diagnose the state of quiescence and identify the onset of surging. Specific objectives include, but are not limited to:
The development of novel geophysical acquisition and processing methods for quantitative analysis of ice properties.
The quantification of glacier surge dynamics using glacier surface feature-tracking algorithms and radar interferometry (InSAR).
Development of a visco-elastic model of surge dynamics, incorporating observed data.
Figure 2. Surge glaciers, and dates of identified surges, of the Vatnajökull ice cap, southeast Iceland. Modified after Ingólffson et al. (2016).
Potential for high impact outcomes
Insight into the controls on glacier stability is applicable to cryospheric regions the world over. The use of small-scale proxy sites to understand controls on ice-sheet stability is truly novel, and will provide a template for many future studies. The geophysical developments made in this project are not only relevant to glaciological analyses, but have applicability in all many branches of seismic investigation. Methods will be reported in the geophysical press, to maximise the visibility of the research outcomes. Research undertaken in this studentship will feed directly into further applications for funding from (e.g.) NERC, where it aligns well with Climate & Climate Change and Terrestrial & Freshwater Environments research areas.
The student will work under the supervision of Dr Adam Booth, Dr Duncan Quincey and Prof Andrew Hooper, within the Institute of Applied Geosciences in the University of Leeds School of Earth and Environment. The project provides high-level specific training in:
appreciation of the significant research themes in the discipline of cryosphere science,
use of state-of-the-art remote sensing approaches,
design, acquisition and quantitative interpretation of geophysical surveys, and
fieldwork in a challenging glacier environment.
Co-supervision will involve regular meetings between all partners. The student can undertake an MSc-level foundation course in Arctic Glaciology during a one-month study programme at the University Centre on Svalbard, in which participants are trained in theoretical and practical glaciological techniques. The successful candidate will have access to a broad spectrum of training workshops facilitated by the DTP, and can access MSc-level modules in both Earth and Environment and Geography to hone skills in geophysical or geographical analysis.
The student should have a keen interest in the quantitative analysis of seismic data, and ideally a background in the application of geophysics in environmental settings. Experience with remotely-sensed data is desirable, and a commitment to undertaking geophysical fieldwork in a challenging environment is essential. Familiarity with programming languages (e.g., Matlab, Python, etc) is also desirable.
Booth AD and 6 others (2012); Thin-layer effects in glaciological seismic amplitude-versus-angle (AVA) analysis: implications for characterising a subglacial till unit. The Cryosphere, 6, 909-922. http://www.the-cryosphere.net/6/909/2012/
Björnsson H and 3 others (2003). Surges of glaciers in Iceland. Annals of Glaciology, 36, 82-90.
Fowler AC and 2 others (2001); Thermally controlled glacier surging. Journal of Glaciology, 47(159), 527-538.
Harrington JA and 2 others (2015); Temperature distribution and thermal anomalies along a flowline of the Greenland ice sheet. Annals of Glaciology, 56(70), 98-104. DOI: 10.3189/2015AoG70A945
Ingólffson O and 7 others (2016); Glacial geological studies of surge-type glaciers in Iceland – Research status and future challenges. Earth-Science Reviews, 152, 37-69. http://dx.doi.org/10.1016/j.earscirev.2015.11.008
Jiskoot H and 2 others (1998); The incidence of glacier surging in Svalbard: evidence from multi-variate statistics. Computers and Geosciences, 24, 387-399. http://dx.doi.org/10.1016/S0098-3004(98)00033-8
Murray T and 6 others (2000); Glacier surge propagation by thermal evolution at the bed. Journal of Geophysical Research, 105(B6), 13491-13507.
Peters LE and 4 others (2012); Seismic attenuation in glacial ice: A proxy for englacial temperature. Journal of Geophysics Research – Earth Surface, 117, F2. DOI: 10.1029/2011JF002201
Quincey DJ and 3 others (2015); Heterogeneity in Karakoram glacier surges. Journal of Geophysics Research – Earth Surface, 120(7), 1288-1300.
Rea BR and Evans DJA (2011); An assessment of surge-induced crevassing and the formation of crevasse squeeze ridges. Journal of Geophysical Research – Earth Surface, 116. DOI: 10.1029/2011JF001970
Siegert MJ and 7 others (2016); Subglacial controls on the flow of Institute Ice Stream, West Antarctica. Annals of Glaciology, 2016, 1-6. http://dx.doi.org/10.1017/aog.2016.17
Related undergraduate subjects:
- Geophysical science