Deformation of volcanic materials by pore pressurization: analog experiments with simplified geometry
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The pressurization of pore fluids plays a significant role in deforming volcanic materials; however, understanding of this process remains incomplete, especially scenarios accompanying phreatic eruptions. Analog experiments presented here use a simple geometry to study the mechanics of this type of deformation. Syrup was injected into the base of a sand medium, simulating the permeable flow of fluids through shallow volcanic systems. The experiments examined surface deformation over many source depths and pressures. Surface deformation was recorded using a Microsoft® Kinect™ sensor, generating high-spatiotemporal resolution lab-scale digital elevation models (DEMs). The behavior of the system is controlled by the ratio of pore pressure to lithostatic loading \((\lambda =p/\rho g D)\). For \(\lambda <10\), deformation was accommodated by high-angle, reversed-mechanism shearing along which fluid preferentially flowed, leading to a continuous feedback between deformation and pressurization wherein higher pressure ratios yielded larger deformations. For \(\lambda >10\), fluid expulsion from the layer was much faster, vertically fracturing to the surface with larger pressure ratios yielding less deformation. The temporal behavior of deformation followed a characteristic evolution that produced an approximately exponential increase in deformation with time until complete layer penetration. This process is distinguished from magmatic sources in continuous geodetic data by its rapidity and characteristic time evolution. The time evolution of the experiments compares well with tilt records from Mt. Ontake, Japan, in the lead-up to the deadly 2014 phreatic eruption. Improved understanding of this process may guide the evolution of magmatic intrusions such as dikes, cone sheets, and cryptodomes and contribute to caldera resurgence or deformation that destabilizes volcanic flanks.
KeywordsAnalog experiments Volcanic pore pressurization Deformation Mechanical failure Flank destabilization Microsoft Kinect sensor
We thank Associate Editor Acocella, Dr. O. Galland, and two anonymous reviewers for their help in improving the manuscript.
The present work was funded by private donations to the University at Buffalo Foundation to study volcanism in the Southern Cascades, and by NASA grant number NNX12AQ10G. The views expressed in the present contribution are those of the authors alone.
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