Volcanism in the Andes occurs in a frontal volcanic arc, but also in the back-arc region. This back-arc volcanism that Tunupa is part of has an uncertain origin; one proposed process is delamination, whereby the lowermost mafic section of the crust and lithosphere underneath separates itself from the above lying layers. This separation process then triggers volcanic activity through either decompression melting, dehydration melting, increases in temperature, or some combination of these processes. Back-arc volcanism in the region started about 25-30 million years ago.