Determining the relative potential of future igneous activity in Germany – a multi-criteria approach

Future volcanic activity within or around distributed volcanic fields is difficult to determine, as many processes affect the melt formation in the mantle and the ascent of melt through the lithosphere. Depending on the external and internal forces and mechanisms, the igneous activity (i.e., shallow intrusive along with extrusive magmatism) can be long lasting or be interrupted by several phases of dormancy. To determine the long-term (i.e., next 1 Myr) relative potential of igneous activity in Germany we therefore suggest to consider the characteristics of various parameters including, among others, seismic anomalies in the mantle, earthquakes, degassing of mantle fluids, ground motion, depth of Moho and LAB, tectonic activity, modelled melt potential based on numerical simulations, and past volcanic eruptions. Thereby, numerical simulations can be used to quantify uncertainties of various parameters describing the structural and thermal state of the lithosphere and the upper mantle. Melt potential calculations including these uncertainties as well as compositional variations of mantle rocks can be used to identify areas of actual critical state with regard to possible future volcanic eruptions below Central Europe.

Based on all 20 parameters investigated, a semi-quantitative multi-criteria method was developed and finally applied to differentiate regions of relative potential for future igneous activity in Germany. Although, most parameters are not uniquely related to magmatic processes, the presence of values exceeding the defined thresholds of any single parameter enhances the potential of future igneous activity at specific locations. Parameter properties are scaled between 0 and 10 within their range of significance (above/below a defined threshold value) to allow their comparison and combination. Weighting factors for individual parameters are used based on the results of expert surveys. However, an index map with statistically determined weighting factors shows the insensitivity of the proposed method in terms of chosen weighting factors.

The results of the multi-criteria method can be used to identify suitable regions for a safe repository for high-level radioactive waste, where areas have to be excluded, which might be directly affected by future magmatic processes. In this context, we computed Germany-wide index (“hazard”) maps, where the index values represent a combination of all 20 parameters. The resulting index maps show that a higher relative potential of future igneous activity occurs not only in regions affected by Quaternary volcanism, but also in and around older Cenozoic volcanic fields or even in regions that have not been affected previously by Cenozoic volcanism. These observations indicate the possible longevity of a geodynamic framework that facilitates magmatic activity over large time scales (millions to tens of millions of years).