Tayo van Boeckel flytur fyrirlestur um verkefni sitt til meistaraprófs í jarðeðlisfræði. Heiti verkefnisins er Relating Subglacial Hydrology to Surface Velocity Variation of Breiðamerkurjökull, Iceland.
Ágrip
How the subglacial hydrology relates to velocity variations has been a topic discussed for many decades. Studies have revealed how changes in sliding, water pressure and water storage do not correlate in phase. The most reliable conclusions are that the overwhelming of the drainage systems results in glacier velocity variations. A dynamically evolving subglacial drainage system can take this into account. Moreover, surface velocity measurements are also affected by longitudinal stress gradients. The combination of both hypotheses is tested against GPS velocity data from Breiðamerkurjökull, Iceland, during 2010, 2012 and 2013. Rain-induced speed-up events show that indeed the overwhelming of the drainage systems causes rapid acceleration, both on time scales of single events as seasons. Ice creep velocities were measured during typical winter weather conditions where sliding is assumed to be negligible. A Full Stokes flowline model agrees with the estimated winter velocities. Sliding velocities are derived after the ice deformation velocities were subtracted. Basal motion generally peaked in spring and decreased during melt season, further indicating that the drainage systems evolves to greater efficiency also on seasonal time scales. However, one anomalous year underlines that the relation could be more complicated. Because no rover measured velocities for an entire year, a relation between average annual temperature and sliding could not be established. In an attempt to address the temporal offset of basal motion, water pressure and water storage, a new conceptual model on the drainage system is presented that combines channels, cavities and sheets. The sliding directly relates to the sheet area rather than to water pressure or water storage. The sheet is created by overwhelming of the drainage system with water, but decreases in size with increasing channel and cavity sizes. Cavities promote a certain amount of sliding, but their expansion leads to the sucking up of water from the sheet, storing it more localized. All in all they serve as a negative feedback on the sliding peak, but prolong the event through slow drainage.
Aðalleiðbeinandi er Alexander H. Jarosch, fræðimaður við Jarðvísindastofnun Háskólans og umsjónarkennari er Guðfinna Aðalgeirsdóttir, dósent við Jarðvísindadeild Háskóla Íslands.
Prófdómari: Tómas Jóhannesson, Veðurstofu Íslands.