Distribution of monogenetic volcanism along the Cameroon Line

Volcanic eruptions may constitute a severe threat for local communities and their infrastructure. Important information as to the prediction of future eruption sites and the likelihood of activity can be obtained by analysis of spatio-temporal eruption pattern in an area of interest. The fact that monogenetic volcanoes, unlike polygenetic ones, erupt only once (within a geologically short period) at a certain spot and then volcanic activity jumps to another spot, renders a quantitative, probabilistic assessment of eruptive cycles challenging. In other words, the purely temporal risk assessment relevant for polygenetic volcanism has to be supplemented by a spatial dimension in case of monogenetic volcanic fields to allow for a combined spatio-temporal forecast.

While the eruption history of many stratovolcanoes along the Cameroon Line (CL) in Central Africa is comparatively well studied, only fragmentary data exists on the distribution and timing of monogenetic volcanism (mainly scoria cones and maars), presumably associated with Quaternary timescales. Here, we undertake an initial step in closing this gap and present for the first time a map of monogenetic volcanic features for most parts of the CL. Scoria cones and maars were identified by their characteristic morphologies using a combination of field knowledge, digital elevation models and satellite imagery. More than ~1300 scoria cones and 41 maars were detected and divided into eight monogenetic volcanic fields (MVF), as defined by the convex hull of the outermost vents: Bioko, Mt. Cameroon, Kumba, Tombel Graben (including Mt. Manengouba), Noun, Oku, Adamawa, and Biu (Nigeria). However, due to the rugged topography in the Oku volcanic field and the difficulty of identifying volcanic features remotely, the number of mapped scoria cones appears rather incomplete.

While the delineation of individual MVF bears an inherent subjective moment, statistical analyses of the primary dataset clearly shows that the mean nearest neighbour distance increases from <1 km to ~2 km from the oceanic sector (Bioko, Mt. Cameroon) in the southwest towards the continental part in the northeast (Adamawa, Biu). Correspondingly, the areal density of monogenetic features decreases along this gradient by about one order of magnitude from >0.2 km^-2 (southwest) to 0.02 km^-2 (northeast). This finding is in general agreement with prior geochronological results, indicating increased Quaternary activity towards the central and oceanic part of the CL (e.g., Njome and de Wit, 2014). Tests for the spatial organization of monogenetic volcanoes using the Geological Image Analysis Software (GIAS, v2; Beggan and Hamilton, 2010) revealed that the vents in all MVF are clustered (98% credible interval), thus allowing inferences to be drawn on the tectonic control of (future) eruption locations.

 

References

Beggan, C., Hamilton, C.W., 2010. New image processing software for analyzing object size-frequency distributions, geometry, orientation, and spatial distribution. Computers & Geosciences 36, 539-549.

Njome, M.S., de Wit, M.J., 2014. The Cameroon Line: Analysis of an intraplate magmatic province transecting both oceanic and continental lithospheres: Constraints, controversies and models. Earth-Science Reviews 139, 168-194.