Numerical Model of the Changes in Geothermal Activity in the Rotomahana-Waimangu System Due to the 1886 Eruption of Mt Tarawera

Abstract

We are modeling the perturbations in the pressure-temperature gradients and the fluid flow paths within the Rotomahana-Waimangu geothermal system caused by the 1886 volcanic eruption of Mt. Tarawera. This short lived eruption destroyed the Pink and White Terraces and led to the subsequent outbreak of geysers and hydrothermal eruptions in the Waimangu Valley. Our conceptual model suggests that most of the changes in surface activity came about as the water table, which lowered about 100 m due to the volcanic eruption, rose over a ~10-year period to near its pre-eruption level by 1895. Geysering and hydrothermal eruptions (1900 to 1917) ensued when hot water rising through narrow vertical conduits had pushed out cold water, which had flooded the shallow subsurface immediately following the volcanic eruption. The changes in surface activity were influenced by effects at relatively shallow depths of <1 km within the geothermal system. Preliminary results suggest that approximately 0.1 km3 of hot water was removed catastrophically during the 1886 eruption. Pressure-temperature gradients and fluid flow stabilized within ~40 years, indicating a relatively short recovery period after the 1886 eruption.