SHALLOW MAGMATISM & VOLCANIC LAKES
Mono Lake in eastern California is an endorheic hypersaline lake where fluid and heat flow are influenced by coupled tectonic, volcanic, biological, and hydrothermal processes. To further constrain how these coupled processes influence fluid and heat flow, we use a lightweight Lister probe that can be deployed from small watercraft to measure temperature gradients and thermal conductivity for estimating shallow conductive and advective heat flow around lava domes and fault zones in Mono Lake. In general, temperature fluctuations in the shallow sediments induced by annual lake temperature fluctuations dominate the shallow temperature gradients. Nonetheless, of 62 campaign temperature gradient measurements collected in 2021-2022, 3 locations exceeded background levels (<3 °C/m) with the highest thermal gradient reaching 8 °C/m. Two of these locations are at Hot Springs Cove southeast of Paoha Island where a lava dome formed approximately 300-350 years BP and the third location is at South Tufa along a fault mapped onshore and identified offshore through seismic reflection data. If the observed temperature gradients are associated with conductive heat transport then estimates of shallow heat flow values at these 3 sites range from 3.5-8.0 ± 3 W/m2. It is more likely that these elevated temperature gradients are associated with combined advective and conductive heat transport around the lava dome and fault, hence these values are minima for the total heat flux. To test this hypothesis, we model multiphase groundwater flow and heat transport in the shallow sediments of Mono Lake using the iTOUGH2 software. We find that heat emanating from conduits transporting multiphase fluids at the temperature measured in fumaroles at Hot Springs Cove and in hot springs along faults near the southern edge of the lake can produce the elevated temperature gradients observed. Significantly, the locations with elevated temperature gradients are aligned with the north-south trend of the Mono-Inyo Craters and Mono Lake volcanic field. Our results provide a guide for a broader survey, measurements over a longer period of time to assess lake temperature effects, and the use of longer probes to better characterize recent volcanic and ongoing hydrothermal activity in the Mono Basin.
Mono Lake Volcanic Field