Reconstructing Tumalo Volcanic Center (Central Oregon Cascades, USA) Eruption Volumes Using ArcGIS

The Pleistocene Tumalo Volcanic Center (TVC) in the Central Oregon Cascades is thought to be the origin of several potentially large-volume explosive eruptions. However, the location of the eruptive vent and the total volume of each eruption are not well constrained. Here we calculate estimated volumes for the Shevlin Park Tuff and the Tumalo Tuff/Bend Pumice units of the TVC and infer a potential vent location using ArcGIS.

We used the geometry of mapped exposures in order to approximate the upper and lower "surfaces" of the units. These approximated surfaces were then interpolated through the use of ArcGIS, utilizing Trend and Kriging methods. The difference between the upper and lower surfaces summed over the mapped extent allows a first-order approximation of eruption volume. This is a minimum volume as the mapped extent is limited and does not cover the full extent of the deposits.

Through the use of Kriging interpolation, within the area of study (approximately 161 km²), the Shevlin Park Tuff is estimated as a minimum of 0.80 km³ and the Tumalo Tuff/Bend Pumice as a minimum of 2.30 km³. Given that these are absolute minimum estimates these results match well with the 5-10 km³ total volume estimates from Hildreth (2007).

Any slopes in a calculated thickness raster—an image that models unit thicknesses—could point towards a vent location. With the utilization of a Trend interpolation, both units trend towards Triangle Hill (44.10°N, 121.54°W), a small previously identified basaltic andesite vent. Both units appear to thin to the southeast, suggesting a source vent to the northwest. This sloping can also be seen in the Kriging interpolation for both units, though not as clearly.

Additional modelling that incorporates local well log data could more precisely determine possible vent locations for these eruptions, while identifying distal deposits can further constrain the total volumes.