Understanding heat and groundwater flow through continental flood basalt provinces: insights gained from alternative models of permeability/depth relationships for the Columbia Plateau, USA

Abstract

Heat-flow mapping of the western USA has identified an apparent low-heat-flow anomaly coincident with the Columbia Plateau Regional Aquifer System, a thick sequence of basalt aquifers within the Columbia River Basalt Group (CRBG). A heat and mass transport model (SUTRA) was used to evaluate the potential impact of groundwater flow on heat flow along two different regional groundwater flow paths. Limited in situ permeability (k) data from the CRBG are compatible with a steep permeability decrease (approximately 3.5 orders of magnitude) at 600-900 m depth and approximately 40°C. Numerical simulations incorporating this permeability decrease demonstrate that regional groundwater flow can explain lower-than-expected heat flow in these highly anisotropic (k x /k z~1 0 4 ) continental flood basalts. Simulation results indicate that the abrupt reduction in permeability at approximately 600 m depth results in an equivalently abrupt transition from a shallow region where heat flow is affected by groundwater flow to a deeper region of conduction-dominated heat flow. Most existing heat-flow measurements within the CRBG are from shallower than 600 m depth or near regional groundwater discharge zones, so that heat-flow maps generated using these data are likely influenced by groundwater flow. Substantial k decreases at similar temperatures have also been observed in the volcanic rocks of the adjacent Cascade Range volcanic arc and at Kilauea Volcano, Hawaii, where they result from low-temperature hydrothermal alteration.

Thermal effect of climate change on groundwater‐fed ecosystems

“…Both eastern and western models assumed a uniform vadose zone thickness of 30 m. Vadose zone thermal conductivity varies as a function of air and water content, but a uniform value of 1.6 W/m/°K is assumed for all flow paths, consistent with estimates for other volcanic terrains in the northwestern U.S. [e.g., Lachenbruch and Sass , ; Brott et al ., ; Burns et al ., ]. Land‐surface temperatures were estimated by averaging the DayMet gridded daily minimum and maximum temperatures for the period 1980–2013 [ Thornton et al ., ], and to account for the influence of increasing mean air temperature (in the DayMet data) along the length of Giant Crater Lava (∼0.1°C/km); the temperatures of groundwater contributions from the east and west were increased at the same rate.…”

Crustal permeability

“…The permeability structure of the uppermost crust is highly heterogeneous and, whereas a wide variety of k-z relations have been suggested, it is risky to extrapolate crustalscale k-z relations to the uppermost crust, or perhaps even to define such relations (e.g. Ranjram et al 2016;Burns et al 2016). The permeability of clastic sediments in the cool Fig.…”

“…Luijendijk and Gleeson 2016;Daigle and Screaton 2016). However, this predictability diminishes at depths where diagenetic processes become important; similarly, hydrothermal alteration of volcanic rocks tends to cause significant reduction of permeability at temperatures in excess of approximately 40-50°C (Burns et al 2016). …”

DigitalCrust – a 4D data system of material properties for transforming research on crustal fluid flow

“…Hydrogeologists, geologists, and geophysicists have begun to actively explore the role of groundwater and other subsurface fluids in fundamental geologic processes, such as crustal heat transfer, ore deposition, hydrocarbon migration, seismicity, tectonic deformation, and diagenesis and metamorphism (e.g., Burns et al 2015;Connolly & Podladchikov 2015;Howald et al 2015;Micklethwaite et al 2015;Miller 2015;Okada et al 2015;Weis 2015). The permeability of the Earth's crust is of particular interest because it largely determines the feasibility of important physiochemical processes, such as advective solute/heat transport (Burns et al 2015;Saffer 2015) and the generation of elevated fluid pressures by processes such as physical compaction, heating, mineral dehydration, and fluid injection (Connolly & Podladchikov 2015;Miller 2015;Weis 2015).…”

“…The permeability of the Earth's crust is of particular interest because it largely determines the feasibility of important physiochemical processes, such as advective solute/heat transport (Burns et al 2015;Saffer 2015) and the generation of elevated fluid pressures by processes such as physical compaction, heating, mineral dehydration, and fluid injection (Connolly & Podladchikov 2015;Miller 2015;Weis 2015).…”