2D numerical simulation of the shallow magmatic body at Krafla

The Krafla caldera, located in the Northern Volcanic Zone of Iceland has become the most studied volcano in the country since its last eruption, the Krafla Fires, happened between 1975 and 1984. From that moment, an extensive monitoring system has been developed in the caldera, focused on both geothermal exploration and production, as well as scientific research. In 2009, the IDDP-1 exploratory well aiming to 4 km depth in search of supercritical hydrothermal fluids got stuck at 2.1 km, retrieving quenched glass cuttings. It was then understood that an unexpected and undetected rhyolitic magma body had been drilled. This body stood without apparent signs of crystallization at the rooftop, opposing the most common belief that magmatic bodies at shallow depths should present a mushy region adjacent to the body’s walls.

We aim to simulate the dynamics of the magma encountered in Krafla. We perform 2D numerical simulations of the magma thermo-fluid dynamics, assuming thermodynamic equilibrium in a sill-like, disk-shaped body 1200 metres wide and 260 metres deep. We include a 100 metres thick aureola with fixed boundary temperature of 350 ºC and initial linear temperature gradient up to 900 ºC in the magmatic body.

In order to simulate the magma dynamics we use the software GALES (Garg and Papale, Frontiers in Earth Sciences 2022), which solves the 4D dynamics of multi-component fluids in geometrically complex domains. Melt-solid-gas thermodynamic are computed with rhyoliteMELTS (Gualda et al., J. Petrol. 2012) using the alphaMELTS-2 front end (Smith & Asimow, GCubed 2005). The properties density, heat capacities, single-phase and multiphase non-Newtonian viscosity, thermal conductivity, and compressibility, are locally computed as a function of pressure, temperature, phase distribution, and phase composition. The results allow a first evaluation of the conditions under which a crystal mush can form and be stable close to the roof and margins of a shallow magmatic intrusion.