Institute of Geophysics of the CAS, v. v. i.

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Volcanic extrusions

Aim of our work is the understanding of internal structure of volcanic bodies in terms of lava/magma flow rheological properties and emplacement conditions. This also requires reconstruction of the original shapes of the volcanic bodies that represent remnants of various subaerial or shallow intrusive volcanic bodies. Field work comprises the Tertiary phonolites and trachytes in Eger-graben rift in Bohemian massif (Czech Republic), phonolite bodies in Black Hills in Wyoming (USA) and dacite lava flows on slopes of Three Sisters volcanoes in Oregon (USA). We combine techniques of structural geology, microstructural analysis and analogue modeling to address the physical processes that control the style and dynamics of lava extrusion. Magmatic fabrics and fracture patterns in the solidified lavas are correlated in terms of the lava emplacement level and dynamics, its original dimensions and cooling boundary conditions. Such information can be used for refining the geohazard mitigation models of volcanic dome growth, where volcanic domes or lava flows collapse with catastrophic consequences (Blong, 1984).

Detailed field investigation of the lavas of interest are supplemented by detailed microstructural investigation of the oriented thin-sections including AMS (anisotropy of magnetic susceptibility), EBSD (Electron Back Scattered Diffraction) and image analysis. Indirect lava rheology quantification from morphometric analysis was also applied on selected lava flows on Mars.

 Dome

Schematic illustration of internal pulse-like structure of Hradiště trachyte cupola (7km E from Teplice town) and associated vertical section of an analogue model prepared with colored plaster (Závada et al., 2009).

USA

Dacite lava flow on the western slopes of the Three Sisters volcanoes (Oregon,USA). The outcrop is carved by glacial erosion.

Research team: Prokop Závada, Matěj Machek, Petr Brož and Aleš Špičák.

Co-workers: František Hrouda (IPSG, Agico, Int.), Karel Schulmann (CGS), Ondrej Lexa (IPSG), Jakub Haloda (CGS) and Patricie Týcová (CGS).

Referenes:

* Blong, R.J., (1984), Volcanic hazards: Sydney, Australia, Academic Press, 424 p.

* Závada, P., Schulmann, K., Hrouda, F., Lexa, O., Haloda, J., and Týcová, P., (2009), The mechanism of flow and fabric development in mechanically anisotropic trachyte lava, Journal of Structural Geology, 31, 11, 1295–1307, DOI: 10.1016/j.jsg.2009.04.002.