Eruptive Cycle and Bubble Trap of Strokkur Geyser, Iceland

Abstract

The eruption frequency of geysers can be studied easily on the surface. However, details of the internal structure including possible water and gas filled chambers feeding eruptions and the driving mechanisms often remain elusive. We used a multidisciplinary network of seismometers, video cameras, water pressure sensors and one tiltmeter to study the eruptive cycle, internal structure, and mechanisms driving the eruptive cycle of Strokkur geyser in June 2018. An eruptive cycle at Strokkur always consists of four phases: (1) Eruption, (2) post‐eruptive conduit refilling, (3) gas filling of the bubble trap, and (4) regular bubble collapse at shallow depth in the conduit. For a typical single eruption 19 ± 4 bubble collapses occur in Phase 3 and 8 ± 2 collapses in Phase 4 at a mean spacing of 1.52 ± 0.29 and 24.5 ± 5.9 s, respectively. These collapses release latent heat to the fluid in the bubble trap (Phase 3) and later to the fluid in the conduit (Phase 4). The latter eventually reaches thermodynamic conditions for an eruption. Single to sextuple eruptions have similar spacings between bubble collapses and are likely fed from the same bubble trap at 23.7 ± 4.4 m depth, 13–23 m west of the conduit. However, the duration of the eruption and recharging phase linearly increases likely due to a larger water, gas and heat loss from the system. Our tremor data provides documented evidence for a bubble trap beneath a pool geyser.

Geysers, Boiling Groundwater and Tectonics: The 3D Subsurface Resistive Structure of the Haukadalur Hydrothermal Field, Iceland

“…This is observed in the Western part of the Hhf where lack of high vegetation mimics the boundaries of the highly resistive region (dashed black lines in Figure 9). The interpretation of this volume as a vapor-saturated reservoir would agree with Eibl et al (2020); Eibl et al (2021) who suggest the occurrence of a shallow bubble trap about 13-23 m West of Strokkur and at about 25-30 m depth. Figure 4 shows that the most prominent hydrothermal features of the Hhf are emplaced at the margins of highly resistive regions.…”

“…It is suggested that Strokkur and Great Geysir geysers develop along vertical fracture-like pipes reaching at least 20 m depth (Pasvanoglu et al, 1998;Torfason & Davíðsson, 1985;Walter et al, 2018). Yet, besides indirect geophysical studies [e.g., Eibl et al (2020) and Eibl et al (2021)] little is known about the plumbing system at depth. Pasvanoglu et al (1998) propose that the ground water system of Hhf is recharged by meteoric waters flowing from the Langjöokull ice-sheet to the North.…”

Eruption Forecasting of Strokkur Geyser, Iceland, Using Permutation Entropy

“…When the seismic source only releases a small amount of energy, and the distance of the source to the station is large, PE seems to reflect more the filtering of the seismic wave during its propagation to the station. This is also supported by the findings of Eibl et al (2021), who could not use these stations for the seismic source location due to low-quality particle motions. By contrast, the drop of PE prior to the 5.6 Mw earthquake at Bárðarbunga two days before the 1996 Gjálp eruption, could be detected by stations at a 100 km distance (Glynn & Konstantinou, 2016).…”

“…The epicenters of the sources were estimated from the intersection of the azimuth angles derived from all 5 stations. Eibl et al (2021) project the epicenter location vertically down and extract the source depth from the intersection point with the derived incidence angles for all stations. Note that the shallow source depths during P1 and peaks in P4 are poorly constrained since the particle motion shows an elliptical particle motion characteristic for Rayleigh waves when the seismic sources reach or approach the surface.…”

“…S1 is located about 10 m to the south of the conduit on the surface. Eibl et al (2021) estimated the source location by using the particle motion of the recorded seismic waves. The epicenters of the sources were estimated from the intersection of the azimuth angles derived from all 5 stations.…”