Doctoral lecture in Geography -  Theresa Bonatotzky

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Ph.D. student: Theresa Bonatotzky

Dissertation title: Weathering of volcanic tephra and its impact on soil formation south of Vatnajökull glacier

Opponents: 
Dr. Randy Dahlgren, Professor at the University of California, Davis, USA
Dr. Goran Durn, Professor at the University of Zagreb, Croatia.

Advisor:
Dr. Guðrún Gísladóttir, Professor at the of the Faculty of Life and Environmental Sciences, University of Iceland
Dr. Franz Ottner, Professor at BOKU University,  Austria
Dr. Egill Erlendsson, Professor at the of the Faculty of Life and Environmental Sciences, University of Iceland

Doctoral committee: 
Dr. Sigurður Reynir Gíslason, Research Scientist at the Institute of Earth Sciences, University of Iceland
Dr. Franz Zehetner, Associate Professor at BOKU University, Austria

Chair of Ceremony: Dr. Anna Dóra Sæþórsdóttir, Professor and the Head of the Faculty of Life and Environmental Sciences, University of Iceland

This is a joint degree between the University of Iceland and BOKU University. The defence took place at BOKU University in June 2021.

Abstract:
Frequent tephra deposition and a steady influx of aeolian material of diverse origin dominate soil formation in Iceland. Little is known about the weathering behaviour, mineral formation and alteration of tephra and Icelandic soils after tephra deposition. This thesis presents the results from extensive studies on soil mineralogy and pedogenesis in various Icelandic soil types and different soil environments.
The sampling sites were selected according to the presence of the light coloured rhyolitic tephra from the Öræfajökull eruption in 1362 CE and a dark-coloured basaltic Veiðivötn tephra from 1477 CE in the volcanically active area south of Vatnajökull, SE Iceland.
All investigated soils were acidic and dominated by sand. Indicated by Feo/Fed ratios above 0.75, they classify as being in an early stage of chemical weathering and soil development. The major portion of the clay size particles are mainly derived from amorphous and poorly crystalline constituents (allophane and ferrihydrite). However, traces of layer silicates (smectite, hydroxy interlayerd minerals and secondary chlorite) were found at all sites. The determining factor of pedogenesis in the histosols was the OM, but the aeolian transport of tephra over long distances and re-deposition as well as local site conditions, rather than the primary composition of the parent material, were the important factors in the development of all investigated soils and the alteration of minerals. Icelandic soils develop in a very dynamic environment. None of the profiles represented a well-developed-pedon, but appeared disturbed over time, showing signs of external influences.

About the doctoral candidate:

Theresa Bonatotzky was born in Vienna, Austria in 1983. She obtained her diploma degree in “Land and Water management” from the University of Natural Resources and Life Science (BOKU), Vienna in 2011. In June 2021, she completed her Joint PhD study from the University of Iceland and from BOKU, Vienna.