1. Department of Geography, Earth System Science; Vrije Universiteit Brussel; Brussels Belgium
2. Laboratoire Magma et Volcans; Université Blaise Pascal; Clermont-Ferrand France
3. GFZ German Research Center for Geosciences; Potsdam Germany
4. Department of Geology and Environmental Science; University of Buea; Buea Cameroon
5. Department of Geology and Soil Science; Ghent University; Gent Belgium