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 remain
elusive. We recorded eruptions at Strokkur in June 2018 with a
multidisciplinary network of seismometers, tiltmeter, video cameras and
water pressure sensors to study the eruptive cycle, internal geyser
structure and driving mechanisms in detail. An eruptive cycle at
Strokkur always consists of 4 phases: the eruption (Phase 1),
post-eruptive conduit refilling (Phase 2), gas filling of the bubble
trap (Phase 3) and regular bubble migration and implosion at depth in
the conduit (Phase 4). For a typical single eruption Phase 1 and 2
persist for 13.1 s. Phase 3 contains a 26.1 s long eruption coda of on
average 19 seismic peaks spaced 1.5 s apart generated at 25 to 30 m
depth, 13 to 23 m west of the conduit when the bubble trap refills with
gas. Phase 4 starts on average 0.9 minutes after the beginning of the
eruption and persists for 2.3 min. In this phase on average 8 large
bubbles leave the bubble trap and implode at a spacing of 24.5 s at
about 7 m depth in the conduit. The duration of the eruption and
recharging phase linearly increases with the number of water fountains
in close succession (Phase 1), likely due to a larger water, gas and
heat loss from the bubble trap and conduit.