Tephra2 - Forward Modeling Tool

Tephra2 Forward Modeling Tool - At a Glance

Tephra2, as a forward modeling tool, calculates the expected accumulation of tephra at locations around an erupting volcano. The code simplifies the eruption conditions, calculating the expected tephra accumulation for a given total eruption mass, eruption column height, and particle size distribution For terrestrial analogs, wind velocity varies as a function of height. Wind velocity is constant within a given stratum. Wind velocities as a function of height are sampled from the NOAA REANALYSIS database for the volcano Tephra2 creates a isomass map, the expected accumulation over a region.

Inputs

An explanation of the forward modeling tool inputs:

• vent location: included are a selection of terrestrial analog volcanoes. Choose a volcano of interest from the pull down menu.
• eruption mass: the total mass of pyroclastic ejecta in kg. Use the slider to select a value; the default value is 10kg.
• plume height: maximum height of the eruption plume expressed as meters above the vent. Use the slider to select a value; the default value is 15m.
• alpha and beta: these parameters identify the Beta distribution which controls the eruption column shape. The shape is strongly dependent on the initial volatile content of the magma. Use the sliders to select values; the default values specify a uniform random distribution, where alpha = beta = 1.
• minimum phi, maximum phi, mean phi, standard deviation (phi units): a log-normal distribution is assumed for the total particle size distribution of pyroclastic ejecta. Use the sliders to select values.
• diffusion coefficient: accounts for coarse-grained particle-particle interaction and turbulence (both in the eruption plume and in the atmosphere for analogous eruptions). Use the slider to select a value between 1 and 1e9 m^2 per s.
• eddy diffusion constant: accounts for fine-grained particle-particle interaction in the atmosphere. Use the slider to select a value between 0 and 1 m^2 per s; the default value is 0.4.
• fall-time threshhold: sets a time (in seconds) indicating when to switch from coarse-grained diffusion to fine-grained diffusion. Use the slider to select a value between 1 and 1e9 s.
• lithic and pumice densities (kg per m^3): Use the sliders to set density values for lithic and pumice particles.
• column steps, particles steps: the plume is divided into equal-size sections and particles are binned into discrete-size ranges to calculate volume using a double integration. Use the sliders to select the number of plume divisions and the number of particle bins; the default values are 200 plume sections and 100 particle bins. Higher values increase runtime of the model; lower values reduce runtime.

After setting input values, press the Run tephra2 button. The code will run on a compute server and send back a message when execution has completed. Execution time varies based on grid size and number of integration steps. Please be patient.

Outputs

• isomass map: mass loading as a function of location given as a PNG image of the deposit contours on topography
• wind rose diagram: visual map (PNG file) of the wind field used by the model. The wind is diagrammed on a circular grid with length of arrow representing wind speed, colors indicating km above sea level, and wind direction drawn as the angular position of the arrow (degrees from North). The wind model is randomly chosen from a database of wind models (4 per day X 360 days) downloaded from NOAA REANALYSIS data (1 year of data) for a location centered on the chosen volcano.
• One way to save a PNG image is to right click on the image and choose an appropriate option.
• Or, use the button, "Choose an output file to download", to select and download any of the available input, output, image, log, or configuration files.