GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 265-3
Presentation Time: 9:00 AM-6:30 PM


GRANDE, Alexandra, Department of Geology, Oberlin College, Oberlin, OH 44074 and HAMPTON, Samuel J., Department of Geological Sciences, University of Canterbury, Christchurch, 8041, New Zealand; Frontiers Abroad Aotearoa, Christchurch, 8041, New Zealand

Analyses of inactive or eroded down volcanoes, as well as their past eruptives, are crucial for understanding volcanic growth over time. The development of new methods for understanding these landscapes is crucial, specifically for inactive eroded volcanoes, as analyses and reconstructions offer insight into landscape surfaces, processes, and the volcanic history of a complex. Remnant features within volcanic landscapes such as planezes and quasi-planar surfaces are features that reflect the slope or paleo-slope of a volcanic complex, and are integral to volcanic reconstructions. Akaroa Volcanic Complex has a highly eroded volcanic landscape, and is a known “erosion” caldera. With its erosional circular crater rim, many reconstructions assume a conical “main vent” structure, yet aspects within the volcanic landscape don’t fully support this. This research looks into the initiating / early stages of Akaroa’s volcanic growth, by examining the quasi-planar surfaces evident within the inner harbour area. GoogleEarthPro provides a platform in which one can identify features, map, and gain perspectives that have not been readily available. It provides a stable platform for 3D representations, data projections and analysis. GoogleEarthPro was used as a base mapping tool, supporting field observations and photograph analysis. Quasi-planar surfaces were mapped and correlated using heights, projections, and cross valley relationships. The correlated quasi-planar surfaces were used to create topographic spot heights from which wireframe models / cone projections could be established and rendered in GoogleEarthPro. Key findings within this study: early eruptions initiated in the upper harbour; progressive over-growth occurred with subtle down harbour vent shifts; early eruptives formed a shallowly dipping (~8˚) volcanic complex. Further evidence which supports this over-growth model is from a recent borehole, which intersected stratified lava flow sequences at depths ~150m below present day sea level. Subtle changes in the landscape and their relationships have provided insights into the early stages of volcanism of the Akaroa Volcanic Complex. And highlight that periods of volcanic growth are recorded within eroded volcanic landscapes, and can be utilized in the reconstruction of volcanic complexes.