Hayes reported activity

Event Name : Hayes Unit II

Stop: 4450 (± 30 Years)

Years BP C-14 (raw)

Debris-avalanche, volcanic avalanche, or landslide:

Description: From Wallace and others (2014): "Immediately overlying the Hayes River ignimbrite of Unit I is a thick sequence of complex mass-flowage deposits that are variable in thickness along the 600 m wide outcrop (fig. 2 [in text]). The relation between Units I and II is unclear, as there is some evidence they may be coeval, but for the sake of clarity we describe these flowage deposits as a separate unit. Immediately above the Hayes River ignimbrite in some places is a 2-4 m-thick sequence of laterally discontinuous,

coarse diamicton that includes rounded to angular boulders as much as 2 m in diameter, which are composed of mostly intrusive rocks (granite, granodiorite) and some indurated clasts of volcanic breccia (figs. 4B, C [in text]). No obviously juvenile material was observed in this part of Unit II. The contact between Unit II and the Hayes River ignimbrite below is erosional in some places but graditional in others (figs. 4B, C [in text]). Where the Hayes River ignimbrite is in direct contact with the overlying diamicton, oxidized gas-escape pipes at the contact and upward into the basal boulder diamicton suggest that the ignimbrite may have been hot when the diamicton was emplaced (fig. 4C [in text]). The upper several meters of Unit II are a poorly sorted, vaguely bedded, matrix-supported, angular-pebble gravel with an oxidized silt-rich upper 25 cm (fig. 4D [in text]). The dominant clast type in this upper portion of Unit II is rounded dense rhyodacite with prominent quartz and feldspar phenocrysts in a light gray (N7) matrix."