Composite Volcanoes II. Morphology of Composite Volcanoes A. Introduction Morphology is one of the most fundamental properties of a volcano, and yet surprisingly little work has been done since the seminal work of Cotton in the 1940s. One of the reasons for this may be the general perception that the morphological evolution of a composite volcano is simple; they are positive (constructional) topographic features, with steep flanks and a general conical shape, and they result from local accumulation of erupted products. However, this simple view ignores the fact that while many composite volcanoes are simple cones with a single summit vent and radial symmetry, many are more complex, compound volcanoes with convoluted histories involving cone collapses, rebuilding, and changing vent locations through time (Table II). Nevertheless, they still display a conical profile normal to the length axis, suggesting a consistency to the "normal" conical shape of a single composite cone. TABLE II Summary of Morphological Types among Composite Volcanoes Another fact that is ignored is that the simple conical shape is the result of a complex evolution that is controlled by the interplay of aggradation and degradation. Short-term aggradation by constructive processes of eruption and emplacement of volcanic materials is opposed by degradation as the longer period destructive processes of erosion, punctuated by catastrophic events such as gravity-driven avalanching (cf. "Debris Avalanches") and posteruption mass wasting. The fact that active composite volcanoes maintain a simple conical shape suggests that the average rate of aggradation must exceed the "punctuated equilibrium" of degradation. Back to Contents