Tephra2

Tephra2 is a tephra dispersion model, that estimates the mass of tephra that would accumulate at a site or over a region, given explosive eruption conditions.

Tephra2 - At a Glance

PDF file (16MB) provides some background on the numerical modeling of tephra dispersion. The tephra2 model simplifies eruption conditions. The code calculates an expected tephra accumulation for a given total eruption mass, eruption column height, and particle size distribution. Wind velocity varies as a function of height but remains constant within a given stratum. Wind velocities are sampled from the NOAA REANALYSIS database at the location of the volcano. Tephra2 outputs the mass per unit area (kg per meter squared) and the weight percent of individual grain sizes at specified locations. The output is presented as a text table of data that can be used to create an isomass map, to visualize expected accumulation over a region.

Inputs

Tephra2 expects the following inputs:

  • volcanic vent location (easting, northing in UTM coordinates)
  • eruption mass (the total mass of pyroclastic ejecta in kilograms)
  • plume height (the height of the erupting column above the vent in meters)
  • alpha and beta (parameters describing a Beta distribution that controls the release height of particles from the plume -- essentially, the shape of the plume; plume shape is strongly dependent on initial volatile content)
  • minimum and maximum size of the pyroclastic ejecta (in phi units)
  • median and standard deviation of the total particle size distribution (in phi units, assuming a log-normal distribution)
  • diffusion constant and fall time threshold (parameters accounting for particle-particle interaction and turbulence, both in the eruption plume and in the atmosphere for analogous eruptions)
  • lithic and pumice particle densities

Outputs

Tephra2 produces the following outputs:

  • a text file table of mass loading as a function of location. The total mass is output and the weight percent of each phi fraction, with format:
    easting(m) northing(m) elevation(m) mass kg/m^2 [max phi size) .... [min phi size)
  • phi bins of weight percent are based on the minimum and maximum size of ejecta chosen

Run a Tephra2 Model

Forward Model »

Probability Model »

Inversion Model »

References

  • The Tephra2 source code can be downloaded from GitHub
  • Bonadonna, C., Connor, C. B., Houghton, B. F., Connor, L., Byrne, M., Laing, A., and Hincks, T. K. (2005) Probabilistic modeling of tephra dispersal: Hazard assessment of a multiphase rhyolitic eruption at Tarawera, New Zealand, Journal of Geophysical Research: Solid Earth 110(B3). DOI 10.1029/2003JB002896
  • Connor, Laura J., and Charles B. Connor (2006) Inversion is the key to dispersion: understanding eruption dynamics by inverting tephra fallout In H. M. Mader, S. G. Coles, C. B. Connor & L. J. Connor (Eds.), Statistics in Volcanology, Geological Society of London Special Publications 231. DOI 10.1144/IAVCEI001.18
  • Biass, Sebastien, Bagheri, Gholamhossein, Aeberhard, William H., and Bonadonna, Costanza (2014) TError: towards a better quantification of the uncertainty propagated during the characterization of tephra deposits, Statistics in Volcanology 1(2):1-27. DOI 10.5038/2163-338X.1.2
  • Biass, S., Bonadonna, C., Connor, L., and Connor, C. (2016) TephraProb: a Matlab package for probabilistic hazard assessments of tephra fallout, Journal of Applied Volcanology 5(1):10. DOI 10.1186/s13617-016-0050-5

The development of Tephra2 was partially funded by grants from the US National Science Foundation.