Tephra are fragments of rock that are ejected from the volcanic edifice during eruption. They play a role near the vent, but at that proximity there are several other hazards which take precedent. The prominent tephra hazard is distal from the vent, after it has traveled very long distances. They can crush infrastructure by collecting, and pose significant threats to aviation.
Methodology: Tephra dispersal from the Mt. Meager Volcanic Complex was modeled using TEPHRA2 software on VHUB. Before beginning analyses, appropriate data were found to enter into the program (Figure 1). Data from Irazu and Mt. St. Helens were used as proxy as they appear in similar tectonic environments. The wind file was created to match the NE trending wind usually felt in the area. Once the analysis was completed in the software, a .txt file needed to be converted to a shapefile for use within the GIS environment. After the shapefile had been created – a collection of points in a grid-like fashion (Figure 2) – it was converted to a TIN, where the mass of tephra accumulated was used as the ‘elevation’ (Figure 3).
Figure 1: TEPHRA2 eruption parameters. Irazu and Mt. St. Helens were used as proxies.
Figure 2: TEPHRA2 data as point data.
Figure 3: Hillshaded TIN of TEPHRA2 data after some processing in ArcMap. The same TIN is used in the final map of tephra dispersion (Fig. 4).
Results:
Figure 4: Hypothetical tephra dispersion from Mount Meager Volcanic Complex.
Based on the map created following the simulation, the largest quantity (as well as being the largest size) of tephra will collect near the vent, most of it being guided by the wind. Interestingly enough, the results of the simulation are similar to the 2360 BC eruption, as evidenced by the location of the two pumice pits. However, as mentioned in the methods section, numbers were estimated for the analyses based on the 1980 eruption of Mt. St. Helens and the 1963 eruption of Irazu, so the results contain significant uncertainty. Once again, they should be used as an educated estimate.