A geophysical investigation of the Eyjafjallajökull glaciovolcanic system, South Iceland, using radio echo sounding

• Main Author: Strachan, Sara M.
• Published: University of Edinburgh 2001
• Subjects: 550
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.662542

This thesis investigates the behavioural dynamics of Eyjafjallajökull, a glaciovolcanic system in South Iceland. The past and present eruptive environment of the volcano and its ice cap are determined by a combination of geophysical and geomorphological methods. The properties and subglacial topography of the ice cap are surveyed by radio echo sounding. Previously identified volcanic landforms on the deglaciated sections of the volcano, integrated with knowledge of subglacial volcanic processes, are used to infer the evolutionary dynamics of the system. Results indicate that Eyjafjallajökull is a special type of system which is highly susceptible to volcanigenic ice disruption. The repeated catastrophic disruption of the ice cap in the past and likely disruption in the future indicates that the marginal fluctuations of the ice cap cannot be solely attributed to climate change. Radio echo sounding experiments conducted at representative sites on the ice cap (crater, flank, toe of Gigjökull) determined the electromagnetic wave propagation velocity in ice at each site: <i>v_crater</i> = 187 ± 23 m <i>ms</i>^-1_,<i>v_flank</i> = 140 ± 8 m <i>ms</i>^-1_,<i>v_Gigjökull</i> = 138 ± 10 m <i>ms</i>^-1. Electromagnetic wave velocity is based on the dielectric properties of the materials through which it propagates. Therefore, the ice in the crater has significantly different dielectric properties than the ice outside the crater. The derived velocities indicate that there are two discrete spatial zones of ice at Eyjafjallajökull: thin, dense ice on the volcanic flanks and at the foot of Gigökull, and thicker ice with a lower bulk density contained within the crater. A well-documented difficulty with the radio echo sounding method is the subjective identification of the ground wave. This obstacle is surmounted by establishing a quantifiable level of uncertainty in waveform interpretation by repeating measurements at each point. Picking uncertainty equals approximately 3 m in ice depth. Ice depths are validated by the experiments, which establish that similar depths can be produced by multiple frequencies. Point data from low frequency radio echo soundings are interpolated to produce maps of the surface and subglacial topography of Eyjafjallajökull.