Search USGS⌕ Search

Geology topics

Andre Revil

Publications and source records attributed to Andre Revil.

4 recordsLinked to original sources
USGS2019

3D electrical conductivity imaging of Halema‘uma‘u lava lake (Kīlauea volcano)

Before the 2018 collapse of the summit of Kīlauea volcano, a ca. 200 m in diameter lava lake inside of Halema‘uma‘u crater was embedded in a very active hydrothermal system. In 2015, we carried out an electrical conductivity survey and the data were inverted in 3D. The lack of conductivity contrast precludes distinguishing the lava column from the surrounding hydrothermal zones. Laboratory measurements on samples from the lava lake show that the conductivity of magma is significantly lower than that of hydrothermal zones but the high vesicularity of the upper part of the lava lake may decrease its macroscopic conductivity. Based on the 3D conductivity model, we distinguish at least two types of hydrothermal circulations: 1) one guided by the collapse faults of Halema‘uma‘u crater and by the magmatic column of the lava lake, and 2) another guided by previous caldera faults and fractures related to intrusions. We observe that the location of the faults formed during the 2018 collapse of the summit was greatly influenced by the hydrothermally altered zones.

Hawaii↗
USGS2015

Sensitivity of airborne geophysical data to sublacustrine and near-surface permafrost thaw

A coupled hydrogeophysical forward and inverse modeling approach is developed to illustrate the ability of frequency-domain airborne electromagnetic (AEM) data to characterize subsurface physical properties associated with sublacustrine permafrost thaw during lake-talik formation. Numerical modeling scenarios are evaluated that consider non-isothermal hydrologic responses to variable forcing from different lake depths and for different hydrologic gradients. A novel physical property relationship connects the dynamic distribution of electrical resistivity to ice saturation and temperature outputs from the SUTRA groundwater simulator with freeze–thaw physics. The influence of lithology on electrical resistivity is controlled by a surface conduction term in the physical property relationship. Resistivity models, which reflect changes in subsurface conditions, are used as inputs to simulate AEM data in order to explore the sensitivity of geophysical observations to permafrost thaw. Simulations of sublacustrine talik formation over a 1000-year period are modeled after conditions found in the Yukon Flats, Alaska. Synthetic AEM data are analyzed with a Bayesian Markov chain Monte Carlo algorithm that quantifies geophysical parameter uncertainty and resolution. Major lithological and permafrost features are well resolved by AEM data in the examples considered. The subtle geometry of partial ice saturation beneath lakes during talik formation cannot be resolved using AEM data, but the gross characteristics of sub-lake resistivity models reflect bulk changes in ice content and can identify the presence of a talik. A final synthetic example compares AEM and ground-based electromagnetic responses for their ability to resolve shallow permafrost and thaw features in the upper 1–2 m below ground outside the lake margin.

The Cryosphere↗
USGS2014

Modeling the hydrogeophysical response of lake talik evolution

Geophysical methods provide valuable information about subsurface permafrost and its relation to dynamic hydrologic systems. Airborne electromagnetic data from interior Alaska are used to map the distribution of permafrost, geological features, surface water, and groundwater. To validate and gain further insight into these field datasets, we also explore the geophysical response to hydrologic simulations of permafrost evolution by implementing a physical property relationship that connects geology, temperature, and ice saturation to changes in electrical properties.

Conference Paper↗