This thesis investigates the behavioral dynamics of Eyjafjallajokull, 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. A total of 425 points at 256 locations were sounded on the ice cap. Of these, 186 are deemed interpretable and used to construct a basal map. The map reveals a number of features underlying the ice cap: a deep (>200 m ice thickness) N-S striking trough in the crater which constitutes the main flow line of ice towards the northern rim breach, an elongate hump in the center of the crater which could be a remnant vent cone, possible parasitic craters on the east flank, and an overdeepening at the base of Gigjokull's icefall. 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 Eyjafjallajokull 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 Gigjokull) determined the electromagnetic wave propagation velocity in ice at each site: crater = 187 +/- 23 m micro-s^-1, flank = 140 +/- 8 m micro-s^-1, Gigjokull = 138 +/- 10 m micro-s^-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 Eyjafjallajokull: thin, dense ice on the volcano flanks and at the foot of Gigjokull, and thicker ice with a lower bulk density contained within the crater. Eyjafjallajokull is spatially split into two glaciological systems based on ice thickness and structure. The area containing the summit crater and its outlet glacier, Gigjokull, is less sensitive to the influence of climate in its current topographical confines. In the event of a summit eruption, the thick, impermeable ice in the crater may confine meltwater, then suddenly release it as a jokulhlaup. Thermal and mechanical erosion from flooding meltwater could severely disrupt the ice of Gigjokull. The area outside the summit crater contains thin (<150 m) ice and a probable well-developed subglacial drainage system. This section is more sensitive glaciologically to climate change and, in the event of an eruption, will allow meltwater to drain continuously, lessening the hazard of flooding. The maximum flood volume at Gigjokull could reach 0.63 km^3. The fluctuations of Gigjokull, compared to the rest of the ice cap, are anomalous. Gigjokull and the rest of Eyjafjallajokull are separate glaciological systems during periods of deglaciation, resulting from differences in their catchment hypsometry. Consequently, it is concluded that the fluctuations of Gigjokull alone are not representative of the oscillations of the ice cap as a whole and should not be used exclusively to make inferences about the past regional climate. This last finding can be applied to glaciovolcanic systems in general. By combining evidence of topographical features from the ice-free areas of the volcano with indications of features inferred from a subglacial surface interpolated from discrete radio echo soundings, a greater understanding of the overall characteristics and dynamics of the Eyjafjallajokull glaciovolcanic system is achieved.