DOES THE MORPHOMETRY OF SCORIA CONES RELATE TO THEIR AGE? RESULTS FROM THE CAMEROON VOLCANIC LINE

For risk assessment and for understanding the spatio-temporal patterns of active phases of a specific volcanic field, it is important to establish an eruption chronology. However, conventional radiometric dating techniques such as the ⁴⁰Ar/³⁹Ar, ¹⁴C or luminescence methods can often not be reliably applied to Holocene and Late Pleistocene volcanoes because the concentration of radiogenic Ar is too low for accurate measurement, organic material is absent, or associated heated country rock for luminescence is lacking. Therefore, alternative approaches are needed. Previously, it was shown that scoria cones – the most frequent type of volcanic edifice on Earth – are characterized by a specific, universal geometry (e.g., Wood, 1980). For a particular climatic zone, it might thus be expected that the morphometry of scoria cones changes as a function of their age, driven by erosion. Specifically, it has been proposed that the ratio of height to basal diameter of the cone is a function of its age, provided that erosional processes acted uniformly since its formation (e.g., Hooper and Sheridan, 1998; Inbar et al., 2011).

The Quaternary scoria cones along the Cameroon Volcanic Line (CVL) represent an example where this approach of relative age assignment might reveal important information on the origin and time-progression of active volcanism. While pre-Quaternary volcanoes of the CVL are comparatively well-dated by ⁴⁰Ar/³⁹Ar, no age information is available for the youngest volcanic manifestations. Not only due to the risk posed to the local population in case of new eruptions, age data is critically required to test hypotheses for the origin of the CVL. We therefore investigated the morpho­metry of a series of scoria cones in the Tombel, Mt. Cameroon and Manengouba volcanic fields as well as the scoria cones of the island Bioko. Based on SRTM data with a horizontal resolution of 12.5 m, slope inclination as well as basal diameter and height were determined using the software ArcGIS. Categorizing geometric parameters allowed us to assign scoria cones to age groups, yielding for the first time a relative chronology for these Quaternary volcanic fields. In the future, we intend to apply luminescence methods to those scoria cones hosting crustal xenoliths to 'calibrate' the determined relationship of geometric parameters and age.