Seismic signatures of some Icelandic geysers

Abstract

Characteristic patterns of seismic activity have been established for the following Icelandic geysers: Strokkur, Uxahver, Reykholtshver, Sodi, and Great Geysir. Strokkur's pattern is a short series of strong, frequently audible, impulsive, one-sided bursts of seismic energy of 1- or 2-second duration, beginning about 9 seconds after the eruption and continuing for a while at 2- or 3-second intervals. Probably sloshing water during the filling of emptied underground cavities generates the pulses. Uxahver's pattern is different: immediately after each eruption the ground suddenly starts to subside and continues at a constant rate for 1–20 seconds, suggesting the collapse of subterranean cavities emptied during eruption. The pattern of Reykholtshver consists of about 40 short pulses in a 27-minute period immediately following eruption, probably caused by intermittent boiling or bumping. The ground is then exceedingly quiet until the next eruption 7 minutes later. Sodi is usually just a hot, boiling spring; when soap was added to it, eruption was preceded by a sustained high-frequency burst of energy, suggesting the liberation of many steam bubbles. The cone surrounding the now quiescent Great Geysir undulates with a periodicity of about 20 seconds.