Preliminary Chemical Studies of Thermal Waters in Lassen Volcanic National Park and Vicinity

Abstract

Most thermal waters in Lassen Volcanic National Park (LVNP) issue as acidic, low C1 hot springs, which are characteristic of vapor dominated hydrothermal systems and cannot be used for liquid chemical geothermometry. Waters from the neutral pH, low C1 hot springs at Drakesbad and in Little Hot Springs Valley may have equilibrated in shallow aquifers, and so both Na-K-Ca and Na-Li geothermometers approach the measured spring temperatures. The high C1 waters at Growler Hot Spring and Morgan Hot Springs, situated south of LVNP, are the most appropriate for liquid chemical geothermometry and indicate subsurface temperatures between 230°C and 240°C. These springs may arise either from boiling at depth and subsequent mixing with meteoric water or from conductive cooling during lateral flow. In either case, the -230°C to 240°C thermal water probably originated inside the park and flowed southward to Morgan Hot Springs.