Our goal in New Zealand, and for the GNG programme, is to find supercritical hydrothermal fluids, NOT magma.
A major challenge common to both deep geothermal exploration and volcanic hazard monitoring is constraining the location of magma at depth. Unfortunately, seeing through kilometres of rock and extensive hydrothermal systems to the underlying magma is a difficult task, and the geophysical methods used to detect and image magma struggle to resolve magma bodies smaller than about a cubic kilometre in size.
Recent unexpected encounters with shallow magma bodies during geothermal drilling campaigns at three volcanoes highlight this problem; in each case, geophysical surveys prior to drilling had failed to detect or warn about the presence of shallow magma. A new paper published in Geology, lead-authored by GNG team member Shane Rooyakkers, discusses possible eruption hazards associated with these shallow pockets of “covert”magma.
Rooyakkers,S. M., Stix, J., Berlo, K., Petrelli, M. & Sigmundsson, F. (2021) Eruption risks from covert silicic magma bodies. Geology.
The paper focuses on the Icelandic volcano Krafla, where exploratory drilling for supercritical fluids as part of the Iceland Deep Drilling Project accidentally, and unexpectedly, encountered rhyolite magma at just 2.1 kilometres depth, abruptly halting drilling. The authors compared the composition of quenched magma recovered from the base of the well with other rhyolite magmas erupted at Krafla, finding a match between the drill-hole magma and rhyolite erupted in 1724 from the nearby Víti crater. This compositional match implies that the shallow magma body encountered during drilling has been present beneath Krafla at least since this time and has previously fed an eruption, yet was small enough to go undetected by the extensive geophysical studies carried out at Krafla since the 1970s.
Krafla is one of the most intensely monitored and studied volcanoes in the world. Yet, if not for accidental drilling encounters, its active shallow silicic magma body would have gone unnoticed. This example serves as a warning to volcanologists that magma bodies capable of erupting can evade detection even at shallow depth, and highlights the need to improve magma detection and imaging capabilities. Knowing where shallow magma resides is also critical for deep geothermal exploration, hence improving the resolution of magma imaging is a core goal of GNG.