Revealing the Underpinnings of Vapor-Dominated Systems in Yellowstone Thermal Areas
Abstract
We are using integrated geochemical and geophysical approaches to develop a conceptual model for groundwater flow paths in Yellowstone hydrothermal basins. These basins have a complex system of groundwaters, with sources that include dilute groundwater recharged by precipitation and deeper hydrothermal fluids. Water chemistry reflects rock leaching, subsurface boiling, and mixing between dilute groundwaters and hydrothermal fluids. Steam separation through subsurface boiling results in a vapor-dominated system at Mud Volcano, Washburn Hot Springs, Hot Springs Basin, and Crater Hills. Steam separation magnifies concentrations of volatile constituents, including H2S(g), NH3(g), and Hg0(g). The oxidation of H2S to SO42- generates H+, resulting in pH values as low as 1.7 in Sulphur Caldron. Thermal alteration of organic matter in lake sediments and carbonaceous sedimentary rocks results in elevated NH3(aq) + NH4+(aq) concentrations in Washburn Hot Springs and Hot Springs Basin. Subsurface boiling of hydrothermal fluids at Crater Hills produces waters with elevated concentrations of Hg+2(aq) and NH3(aq) + NH4+(aq), with Cl- as the dominant anion. A 2016 helicopter-borne electromagnetic survey (HEM) reveals a subsurface structural perspective of thermal alteration and groundwater flow paths. Water significantly lowers the resistivity of porous volcanic rocks, highlighting boundaries between and within volcanic flows. Hydrothermal alteration that marks present and past fluid flow paths lowers both resistivity and magnetization. All four thermal areas are characterized by low magnetic anomalies and resistivities (<30 ohm-m), reflecting water saturated hydrothermal alteration, especially Mud Volcano, where resistivities can be <3 ohm-m. Higher resistivities (~100 ohm-m) near Sulphur Caldron correspond to a vapor zone encountered in well Y-11 and in a previous electrical survey. Steeply dipping boundaries visible in all the resistivity cross sections are interpreted to represent regional fracture fabric, suggesting pathways for hydrothermal fluids at lower elevation springs associated with Crater Hills and Mud Volcano. This resolution of groundwater architecture presents an opportunity to refine our conceptual models for the evolution of thermal water in vapor-dominated systems.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V33D0213H
- Keywords:
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- 4302 Geological;
- NATURAL HAZARDS;
- 7280 Volcano seismology;
- SEISMOLOGY;
- 8424 Hydrothermal systems;
- VOLCANOLOGY;
- 8488 Volcanic hazards and risks;
- VOLCANOLOGY