Springs on and in the vicinity of Mount Hood volcano, Oregon

Chemical and isotopic data are presented for nonthermal, thermal, and slightly thermal springs and drill holes and fumaroles on Mount Hood, Oregon. Temperatures of nonthermal springs on Mount Hood decrease with elevation and are similar to air temperatures from nearby weather stations. Dissolved constituents in nonthermal springs generally increase with spring temperatures and reflect weathering of volcanic rock from the action of dissolved carbon dioxide. Isotopic contents of nonthermal springs follow a local meteoric water line and generally become lighter with elevation. Some nonthermal springs at low-elevation have light values of isotopes indicating a high-elevation source for the water. Three hydrothermal systems have been identified on Mount Hood. Swim Warm Springs is interpreted to have a source water that boiled from 187?C, re-equilibrated at 96?C, and then mixed with nonthermal water to produce the range of compositions found in various springs. The Meadows Spring is interpreted to have a source water that boiled from 223?C, re-equilibrated at 94?C, and then mixed with nonthermal water to produce the range of compositions found in the spring over several years. Both systems contain water that originated as precipitation at higher elevation. The summit fumaroles have gas geothermometer temperatures generally over 300?C, indicating that they are not the steam discharge from the Swim and Meadows hydrothermal systems. Representative values of thermal discharge for the three hydrothermal systems are 10 MWt for the fumaroles, 2.2 MWt for Swim, and 1.9 MWt for the Meadows and Cascade springs.