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Abstract

Geometric analysis was used to define seven morphometric parameters for the description of the shape of scoria cones, including volume, orientation and five shape parameters (flat-topped-ness, steep-sided-ness, relative crater depth, crater slope and elongation). The measurement and analysis of these shape factors for five distinct scoria cone populations facilitated an exploration of the overlapping effects of growth and erosion processes on shape. Flat-topped-ness seemed to be insensitive to either growth or erosion, suggesting a dependence on eruption energetics. Most of the variation in steep-sided-ness originated from eruptions ending during variable (early to mature) stages of development (growth) and from erosional processes, although steep-sided-ness was also sensitive to eruption energetics (through fragmentation and its impact on the angle of repose). Steep-sided-ness was therefore a poor indicator of geomorphic age. Distinct types of scoria cone shape (ideal, gully, horseshoe, tilted, crater row, parasitic and amorphous) captured a variety of deviations in shape from the purely conical, yet the conical shape parameters differed little in average value between the shape types. The conical shape parameters captured the growth and erosion processes (e.g. ballistic delivery, tephra redistribution via avalanching and erosional transport) common to all scoria cones rather than the particular processes that made the shape types unique (e.g. breaching, rafting and wind effects).

Supplementary material: Locations of examples of the shape types are available at https://doi.org/10.6084/m9.figshare.c.3661907

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