Persistent multitiered magma plumbing beneath Katla volcano, Iceland

Abstract

Recent seismic unrest and a persistent Holocene eruption record at Katla volcano, Iceland indicate that a near‐future eruption is possible. Previous petrological investigations suggest that Katla is supplied by a simple plumbing system that delivers magma directly from depth, while seismic and geodetic data also point toward the existence of upper‐crustal magma storage. To characterize Katla's recent plumbing system, we established mineral‐melt equilibrium crystallization pressures from four age‐constrained Katla tephras spanning from 8 kyr BP to 1918. The results point to persistent shallow‐ (≤8 km depth) as well as deep‐crustal (ca. 10 – 25 km depth) magma storage beneath Katla throughout the last 8 kyr. The presence of multiple magma storage regions implies that mafic magma from the deeper reservoir system may become gas‐rich during ascent and storage in the shallow crust and erupt explosively. Alternatively, it might intersect evolved magma pockets in the shallow‐level storage region, and so increase the potential for explosive mixed‐magma ash eruptions.

The Katla volcanic system imaged using local earthquakes recorded with a temporary seismic network

“…It is interesting that Budd et al . [] find a clinopyroxene crystallization depth in Katla rhyolites concentrated at a similar depth to the depth of the base of the low‐velocity anomaly inside the caldera in our model. The crystallization depths for minerals in Katla basalts (cpx and plag) lie deeper and are more distributed up to about the same depth [ Budd , ].…”

“…We suggest that the core of high velocities at depth beneath the caldera corresponds to these cumulates. Fractionation in the magma lens and assimilation with its host rock will produce rhyolites [ Budd et al ., ] and accumulate above the lens. It is interesting that Budd et al .…”

“…These may derive from deeper magma reservoirs that may erupt directly to the surface or interact with the proposed shallow felsic reservoir, providing heat and potentially mobilizing its felsic melt in a similar way as appears to have occurred at Eyjafjallajökull in 2010 [ Sigmundsson et al ., ; Keiding and Sigmarsson , ; Moune et al ., ]. This process can explain the low δ 18 O values that are found around Katla [e.g., Budd et al ., ] and other Icelandic volcanoes [e.g., Gunnarsson et al ., ; Berg , ]. It does not require a persistent shallow primary (basaltic) magma reservoir [ Óladóttir et al ., ].…”

Magma storage beneath Grímsvötn volcano, Iceland, constrained by clinopyroxene‐melt thermobarometry and volatiles in melt inclusions and groundmass glass

“…The OPAM phase equilibria was already applied to estimate crystallization pressure for several Icelandic basalts [ Kelley and Barton , ], whereas Budd et al . [] and Geiger et al . [] applied the Putirka [] cpx‐liq barometer by selecting what they term as “appropriate nominal melt composition.” In the absence of measurable liquid composition adjacent to the cpx due to highly palagonized glasses and/or crystallized groundmass in the studies of Budd et al .…”

“…[] applied the Putirka [] cpx‐liq barometer by selecting what they term as “appropriate nominal melt composition.” In the absence of measurable liquid composition adjacent to the cpx due to highly palagonized glasses and/or crystallized groundmass in the studies of Budd et al . [] and Geiger et al . [], the authors suggest adoption of a “plausible whole‐rock composition.” However, Óladóttir et al .…”