An Experimental Approach to Understanding the Nature and Origin of Calderas

Michigan Technological University, Houghton MI

Investigators

Abstract

Abstract EAR-0125631 Vallance and Stix Michigan Technological University This proposal aims to advance the accuracy and application of scaled analogue models of caldera formation. Until recently, experimental models have struggled to accurately reproduce the caldera forming process. While new models illustrate that the collapse process is starting to be understood, they do not address the complexities that are inherent in real calderas. We have already developed a basic experimental setup which investigated the effects of varying the magma chamber depth, pre-existing topography, magma chamber pressure, and cross-sectional symmetry. The crust is scaled as sand in these and earlier experiments. Due to compaction effects, the sand appears to deform in a time-dependent fashion. Therefore, our improvements to this basic model will include: (1) scaling the rheological variability of the wallrocks and the magma chamber by using a sill-like, water-filled chamber contained within a silicone jacket; (2) measuring the pressure fluctuations within the chamber; (3) varying the timescales of eruption (chamber evacuation) relative to tectonic and intrusion processes; and (4) gradually adding material to the surface of the collapsing block so as to model emplacement of intracaldera ignimbrites. Experimental calderas that are produced purely from the collapse of a homogeneous subsiding block may have limited application to the complex structural relationships observed at actual calderas. This proposal will model four structural elements that are critical to the caldera-forming process but are poorly understood: 1) precursory tumescence; 2) pre-existing faults; 3) extension and transtension; 4) resurgence.