Háskóli Íslands

On Monday, 11 March Ásta Rut Hjartardóttir is going to defend her PhD thesis: „Fissure swarms of the Northern Volcanic Rift Zone, Iceland“. The lecture will be held in room N-132 in Askja and starts at 14:00.
 
The opponents are Dr. Jeffrey A. Karson Professor at Syracuse University in New York og Dr. Roger Buck Lamont Research Profeesor at Lamont-Doherty Earth Observatory, Columbia University in New York.
 
Supervisors of the PhD were Dr. Páll Einarson, Professor at the Faculty of Earth Sciences, University of Iceland, Dr. Kristján Sæmundsson, Scientist at Ísor og Dr. Haukur Jóhannesson, Scientist.

Ásta Rut Hjartardóttir was born 17 May 1978. She finished bachelors degree in geology in 2003, and masters degree in geophysics in 2008 from the University of Iceland.  In 2009 she started her PhD studies.  The PhD project was supported by the  Eimskip University Fund, and by the Iceland Research Fund.  
 
Dr. Magnús Tumi Guðmundsson, Professor and head of the Faculty of Earth Sciences, will conduct the ceremony.

Abstract
The Northern Volcanic Rift Zone, Iceland, is a ~200 km long segment of the Mid-Atlantic plate boundary, where the North American and the Eurasian plates are diverging.  The rift zone consists of about 5-6 volcanic systems with central volcanoes and fissure swarms, in addition to the Tungnafellsjökull Volcanic System at the border of the rift zone.  The volcanic systems are the locus of eruptive activity in the Northern Volcanic Rift Zone.  The central volcanoes consist of elevated massifs, high temperature geothermal areas, calderas and silicic formations.  Fissure swarms with eruptive fissures and high density of fractures extend in opposite directions from the central volcanoes.  In the Northern Volcanic Rift Zone, the fissure swarms are between 0.5 and 15 km wide and between 30 and ~125 km long.  In this study, fractures and eruptive fissures within the fissure swarms of the Northern Volcanic Rift Zone were mapped in detail from aerial photographs.  The results of the study indicate that eruptions are less common at the distal parts of the fissure swarms than closer to the central volcanoes.  The proximal parts of the fissure swarms also generally show higher fracture density, even when the effect of the age of the lava flows has been taken into account.  Older lava flows in the Krafla and Askja Fissure Swarms have usually higher fracture densities, suggesting repeated dike intrusions into the same parts of the fissure swarms during Postglacial times.  Fractures in the fissure swarms of the Northern Volcanic Rift Zone are characteristically oriented towards north or NNE, i.e. more or less perpendicular to the spreading direction.  However, deviations from this pattern occur in certain areas.  These areas include the caldera volcanoes in the Northern Volcanic Rift Zone, Krafla and Askja, where some fractures and eruptive fissures are concentric to, or radiate from the calderas.  Second example involves east-west oriented fractures and eruptive fissures near the Vatnajökull glacier, and third example eroded WNW-oriented fractures that can be found intermittently through the Northern Volcanic Rift Zone, from the north end of the Kverkfjöll Fissure Swarm to the south end of the Krafla Fissure Swarm.  Other examples involve the previously known WNW oriented transform zones north of Iceland that connect with the Northern Volcanic Rift Zone.  The transform zones influence the fissure swarms, although surface fractures that belong to them are not visible, except in the Þeistareykir Fissure Swarm.  The number of fractures peaks and a graben widens to the north at the intersection of the Húsavík Transform Zone and the Krafla Fissure Swarm, indicating a buried continuation of the transform zone beneath the fissure swarm.  Several fractures at the intersection of the Grímsey Oblique Rift and the Fremrinámar Fissure Swarm are WNW-oriented, as opposed to the general N to NNE oriented fissure swarms, suggesting an onshore continuation of the transform zone.

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