Directional flank spreading at Mount Cameroon volcano: Evidence from analogue modeling

摘要

Mount Cameroon is characterized by an elongated summit plateau, steep flanks, and topographic terraces around its base. Although some of these features can be accounted for by intrusion-induced deformation, we here focus on the contribution of edifice-scale gravitational spreading in the structure of Mount Cameroon. We review the existing geological and geophysical data and morphostructural features of Mount Cameroon and surrounding sedimentary basins. Volcanic ridge gravitational spreading is then simulated by scaled analogue models on which fault formation is recorded using digital image correlation. Three sets of models are presented (i) models recorded in cross section (Type I), (ii) models recorded from above with a uniform (Type IIa), and (iii) nonuniform ductile layer (Type IIb). Type I models illustrate the formation of faults accommodating summit subsidence and lower flank spreading. Type IIa models favor displacement perpendicular to the long axis, with formation of a summit graben and basal folds, but fail to reproduce the steep flanks. Type IIb models investigate the effect of spatial variations in sediment thickness and/or properties consistent with geological evidence. Directional spreading of the volcano’s central part perpendicular to the long axis is accounted for by a sediment layer with restricted lateral extent and increasing thickness away from the volcano axis. The later model closely reproduces key features observed at Mount Cameroon: steep upper flanks are accounted for by enhanced lateral spreading of the lower flanks relative to the summit. The relevance of these findings for understanding flank instabilities at large oceanic volcanoes is finally highlighted.