Probabilistic modeling of tephra dispersal: Hazard assessment of a multiphase rhyolitic eruption at Tarawera, New Zealand

Abstract

[1] The Tarawera Volcanic Complex comprises 11 rhyolite domes formed during five major eruptions between 17,000 B.C. and A.D. 1886, the first four of which were predominantly rhyolitic. The only historical event erupted about 2 km 3 of basaltic tephra fall (A.D. 1886). The youngest rhyolitic event erupted a tephra fall volume more than 2 times larger and covered a wider area northwest and southeast of the volcano ($A.D. 1315 Kaharoa eruption). We have used the Kaharoa scenario to assess the tephra fall hazard from a future rhyolitic eruption at Tarawera of a similar scale. The Plinian phase of this eruption consisted of 11 discrete episodes of VEI 4. We have developed an advection-diffusion model (TEPHRA) that allows for grain size-dependent diffusion and particle density, a stratified atmosphere, particle diffusion time within the rising plume, and settling velocities that include Reynolds number variations along the particle fall. Simulations are run in parallel on multiple processors to allow a significant implementation of the physical model and a fully probabilistic analysis of inputs and outputs. TEPHRA is an example of a class of numerical models that take advantage of new computational tools to forecast hazards as conditional probabilities far in advance of future eruptions. Three different scenarios were investigated for a comprehensive tephra fall hazard assessment: upper limit scenario, eruption range scenario, and multiple eruption scenario. Hazard curves and probability maps show that the area east and northeast of Tarawera would be the most affected by a Kaharoa-type eruption.

A review of volcanic ash aggregation

“…These models include analytical solutions, used widely for investigations of particle sedimentation and for hazard assessments (e.g., Armienti et al, 1988;Bonadonna et al, 2005a;Bursik et al, 1992a and b;Connor et al, 2001;Connor and Connor, 2006;Glaze and Self, 1991;Hurst and Turner, 1999;Koyaguchi and Ohno, 2001a;Macedonio et al, 2005;Suzuki, 1983), and numerical models for real-time forecast of plume evolution and sedimentation (e.g., Costa et al, 2006;Searcy et al 1998). Both types have been validated with field data and are now used regularly for both these purposes.…”

Tephra Fall Simulation for the Eruptions at Mt. Shinmoe-dake during 26-27 January 2011 with JMANHM

“…TEPHRA2 originally developed by Bonadonna et al (2005) gives analytical solution on the tephra loading on the ground. FALL3D is an off-lined Eulerian dispersion model developed by Costa et al (2006).…”

Theoretical background and recent progress of the pyroclastic fall simulation code Tephra2 : essence for application in Quaternary research

“…Tephra2 is a code to simulate deposit distributions caused by pyroclastic eruptions (Connor et al, 2001 ;Bonadonna et al, 2005). The code, which is based on an advectiondiffusion model, has a potential to reconstruct ancient eruptions from limited deposit data.…”