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Tracking mineral precipitation, dissolution, and alteration below volcanic lakes using vertical temperature profiles

Zachary D. Smith 1, Matthew Hornbach2, Michael Manga1

  • Affiliations: 1University of California Berkeley, Department of Earth and Planetary Science, Berkeley, CA 94720; 2Southern Methodist University, Department of Earth Sciences, Dallas, TX 75275 

  • Presentation type: Poster

  • Presentation time: Friday 16:30 - 18:00, Room Poster Hall

  • Poster Board Number: 81

  • Programme No: 6.8.7

  • Theme 6 > Session 8

Abstract

Heat, groundwater, and CO2 flow beneath volcanic lakes is controlled by the evolution of structures and water-rock interactions. We couple new campaign lake floor heat flow measurements and long-term water column temperature monitoring to characterize variations in heat flow controlled by dissolution, precipitation, and alteration of minerals in the sediments below volcanic lakes. Our study is focused on Mono Lake in eastern California which hosts 350-700-year-old volcanic features. We collected 62 shallow (<1.5 m penetration) temperature profile measurements. Heat flow, vertical fluid velocity, and bulk thermal diffusivity are estimated by solving the advection-diffusion equation using long-term water column temperature monitoring data to constrain boundary conditions and reducing misfit between modeled and observed temperatures. On the southern shores of Mono Lake, faults connected to deeper magmatic systems transport groundwater and CO2 into the lake. Within these fault zones, we observe two different types of sublacustrine springs. One set has near surface fluid temperatures of ~30 °C and contains magmatic CO2 that lowers the pH (6-7) relative to the lake water pH (10-11). Up flow at these springs dissolves carbonate minerals resulting in thermal diffusivity of ~2.5x10-7 m2/s. Cool (~20 °C) groundwater emerging from below the lake not containing CO2 reacts with the lake water to precipitate carbonates in the shallow sediments, elevating thermal diffusivity to ~7x10-7 m2/s. These results show promise for using temperature monitoring to track fluid flow, and mineral precipitation, dissolution, and alteration associated with active hydrothermal and shallow magmatic processes below volcanic lakes.