Recharge and Flow in the Medicine Lake Volcano-Fall River Springs Groundwater Basin, California

Isotopic measurements of the 34m(3)/s discharge from the Fall River Springs of northern California indicate recharge from 50km upgradient in high elevation regions of Medicine Lake Volcano. Age determinations suggest less than 20-year travel time. Data demonstrate Klamath Basin further north cannot be a recharge source. Mass balance calculations support that annual precipitation on the volcano supplies observed spring discharge, requiring 50%-75% recharge rates. Radiocarbon and delta C-13 of dissolved inorganic carbon indicate 30%-40% is derived from magmatic CO2. Measured excess He-3 is also consistent with the presence of magmatic gas derived from the Quaternary Age Medicine Lake Volcano.