Geophysical imaging of the hydrothermal system of the Krafla geothermal area

february-july 2022

The Krafla geothermal area is located within a large caldera crossed by a fissure zone and is characterized by intense heat flow and hydrothermal alteration associated to the presence of magma at a 2 km depth as evidenced accidentally during geothermal drilling (e.g. Arnason et al., 2020). The area has been extensively studied with various geophysical imaging methods and drilling. In this study, we will use a high resolution drone magnetic survey recently collected over a large portion of the Krafla caldera and geothermal area to infer information about the distribution of hydrothermal alteration at depth and of geophysical structures that influence the fluid flow. This survey shows strong variations of the magnetic field intensity including a magnetic low that suggests a decrease of magnetization due to the presence of weakly-magnetic intensely-altered volcanic rocks (Olivia-Urcia et al., 2011). The data will be interpreted by constructing forward and inverse models and will incorporate information from a geological model constructed from drill hole data (Mortensen et al., 2015), magnetic properties measured on drill hole samples (Olivia-Urcia et al., 2011) and other geophysical data such as a resistivity model deduced from magneto-telluric data (Lee et al., 2020). During the internship, the student will perform the analysis and interpretation of the magnetic data by writing and using existing matlab or python scripts as well as using a software specialized in the processing and modeling of magnetic surveys. The student might be involved at the end of the internship in a 15 day field work session in Krafla where new drone-borne magnetic surveys will be acquired to complement the existing dataset.

Arnason, K., New Conceptual Model for the Magma- Hydrothermal-Tectonic System of Krafla, NE Iceland, Geosciences 2020, 10, 34 ; doi:10.3390/geosciences10010034

Lee, B., Unsworth, M., Árnason, K., & Cordell, D. (2020). Imaging the magmatic system beneath the Krafla geothermal field, Iceland : A new 3-D electrical resistivity model from inversion of magnetotelluric data. Geophysical Journal International, 220(1), 541-567.

Mortensen AK, Guðmundsson Á, Steingrímsson B, Sigmundsson F, Axelsson G, Ármannsson H, Björnsson H, Ágústsson K, Sæmundsson K, Ólafsson M, Karlsdóttir R, Halldórsdóttir S, Hauksson T, The Krafla geothermal system : a review of the geothermal system and a revised conceptual model (in Icelandic). Tech. rep. Landsvirkjun, Reykjavik, Iceland ; 2009.

Oliva-Urcia, B., Kontny, A., Vahle, C., & Schleicher, A. M. (2011). Modification of the magnetic mineralogy in basalts due to fluid–rock interactions in a high-temperature geothermal system (Krafla, Iceland). Geophysical Journal International, 186(1), 155-174.