Conduit Processes at the Haukadalur Geyser‐Hosting Hydrothermal Field (Iceland) Revealed by In Situ Temperature and High‐Speed Camera Measurements

Abstract

Geysers fascinate scientists and visitors for several centuries. However, many driving mechanisms such as heat transfer in the conduit and in the subsurface remain poorly understood. We document for the first time transient temperature variations inside the active Strokkur's and nearby quasi‐dormant Great Geysir's conduits, Iceland. While recording temperature inside the conduit, we visually monitored Strokkur's activity at the vent with a high‐speed camera, providing a high temporal resolution of the eruptions. Our results reveal heat transfer from a bubble trap to and through the conduit. We propose a model for the eruptive cycle of Strokkur that includes vapor slug rise, eruption, and conduit refill. Each water jet of an eruption is marked by an initial pulse of liquid water and vapor, emitted at a velocity between 5 and 28 m/s and generally followed by a second pulse less than a second later. The timing of eruptions coincides with temperature maxima in the conduit. After the eruption, the conduit is refilled by water falling back in the pool and drained from neighboring groundwater‐saturated geological units. This results in a temperature drop, the amplitude of which increases with depth while its period is reduced. This reflects faster heat transfer in the deeper than shallower part of the conduit. The amplitude of temperature drop following an eruption also increases with the eruption order, implying larger heat release by higher‐order eruptions. Temperature in the conduit subsequently increases until the next eruption, starting then a new cycle.

Video camera and seismic monitoring of water bulge explosion at Strokkur Geyser, Iceland

“…In such cases, the energy released during the eruption is thus efficiently channeled into a large bulge and a large jet, while not generating much seismic ground motion. In contrast, larger jets are followed by a longer waiting time for the next one, and Collignon et al [2023] confirmed that more energy is lost during large eruptions, which must be supplied by the heat source at depth at a possibly constant rate.…”

“…number 52 in Figure 5). This indicates that some water jets are actually composed of multiple pulses, possibly caused by multiple or more complexly shaped bubbles (see work by Collignon et al [2023] for more detail on pulses).…”

“…We derive rising bubble velocities that increase from 0.9±0.5 m s −1 to 2.3±1.1 m s −1 in the frame before the bubble bursts. Collignon et al [2023] measured at Strokkur in 2018, a velocity of 1 to 4 m s −1 in the frame before the bulge bursts. They studied 14 bulges with a high speed camera.…”

“…We note (i) that the conduit is narrowing with depth and shaped rather elliptically in plane view, (ii) that rising bubbles coalesce and expand, and (iii) that the bubbles might be vertically elongated such as in slug flows so that the suggested values are highly conservative. For more discussion around slug flow, the dynamics of a wake of recirculating water following it at Strokkur, the reader is referred to Collignon et al [2023].…”

“…For example, infrasound signals compared to video cameras have been used at some Yellowstone geysers to infer the pressure field during eruptions [Quezada-Reyes 2012]. Pressure and temperature sensors have been used to study recharge and discharge processes [Hutchinson et al 1997;Collignon et al 2023]. For example, multidisciplinary studies have used tiltmeters, acoustic sensors, flow pressure sensors, and temperature sensors to infer that boiling due to pressurization drives Onikobe Geyser, Japan [Nishimura et al 2006].…”