OVERVIEW

tephra2 (VERSION 2.0) is a tephra dispersion simulation tool, written in C, used to estimate the mass of tephra that will accumulate at a site or over a region, given explosive eruption conditions. 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.

Two executables can be compiled, tephra2_2020 (the forward model) and tephra2-inversion_2020 (the inversion model). The inversion model requires MPI (Message Passing Interface) libraries and should be run on a compute cluster with multiple compute nodes.

COMPILING

tephra2 is written in C, a compiled language, and must be compiled before it can be executed. See README for some quickstart instructions. Specifically, to compile the linux executables, in the top level directory, on the command line type:

make

This will compile both the forward model and the inversion model. If you do not have openmpi installed the inversion model will fail to compile, but the forward model will still be compiled. This is OK if you only want the forward model.

INSTALL THESE DEPENDENCIES BEFORE COMPILING

• gcc
• openmpi
• gc, gc-devel, libatomic_ops (for opensuse linux) or libgc-dev, libgc1c2 (for ubuntu linux) or bdw-gc (mac - homebrew)

WIND DATA

How to download NOAA REANALYSIS data to create wind files for tephra2

USAGE

Both the forward model and the inversion model require a configuration file. The configuration file is arranged as a list of keywords followed by their corresponding value(s). The program user can change any of the values; the keywords must not be changed.

To run the forward model, at the command line, type:

tephra2_2020 tephra2.conf grid_file wind_file > tephra2.out

where,

• tephra2_2020 is the name of the executable
• tephra2.conf is the name of the file of configuration parameters (an example)
• grid_file is is a text file of 3 columns separated by spaces (an example) following the format:

  Easting(m)  Northing(m)  Grid-Elevation(m)

• wind_file is a 3-column text file of wind data (an example) following the format:

  Height(masl)  Wind-Speed(m/s)  Wind-Direction(wind vector azimuth in degrees)

• tephra2.out is the output file name where the tephra accumulation values will be written, following the format:

  Easting(m)  Northing(m)  Grid-Elevation(m)  Mass(kg/m^2) [weight percent of modeled phi fractions]

  To run the inversion model, at the command line, type:

  mpirun -np nodes -hostfile machines tephra2-inversion_2020 tepha2-inversion.conf data_file wind_file

  where,

• mpirun is the wrapper script for gcc when using mpi libraries
• nodes is the number of cluster compute nodes to use
• machines is a text file listing the name of each compute node and the number of cpu cores useable on that node (an example)
• tephra2-inversion_2020 is the executable name
• tephra2-inversion.conf is the file of parameters (an example)
• data_file is a text file of tephra accumulation data from chosen area (an example) following the format:

  Easting(m)  Northing(m)  Grid-elevation(m)  Mass(kg/m^2)

• wind_file is a text file of wind data to use for the inversion (same format as above)

ADDITIONAL DEPENDENCIES

• perl
• gmt5
• ncdump

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versions --

01-27-2018 Formally versioning this version of tephra2 as Version 2.0, to distinguish it from other, earlier versions.

03-12-2014 Initial upload of the tephra2 probability scripts (perl scripts) which use the tephra2 model of ash dispersion to create survivor curves for specific locations around a volcano.

07-09-2013 Initial upload to GitHub. tephra2 is a tephra dispersion model based on an analytical (closed-form) solution of the advection-diffusion equation. This initial version uses a plume model based on the beta function and incorporates a 2-D wind model that varies in speed and direction with changes in elevation.