Akutan reported activity

Event Name : Akutan Broad Bight Valley Lahars

Start: 1611

Years BP Tephrochronology

Lahar, debris-flow, or mudflow:

Description: From Waythomas (1999): "Broad Bight valley is a wide glacial valley on the south side of Akutan Island, southeast of the caldera (Fig. 1 [in original text])."

"Lahar deposits in the middle part of Broad Bight valley (sections 58, 70, 71, Fig. 12 [in original text]) form a downstream thinning fan that covers the valley floor to a depth of at least 2 m. These lahar-runout deposits are distinctly finer grained (largest clasts are pebble size) and contain a greater percentage of fines (silt+clay) than their upstream counterparts. At section 87 (Fig. 12 [in original text]) lahar runout deposits overlie the Akutan tephra. Indicating that most, if not all, of the lahar deposits in Broad Bight valley are younger than the tephra."