Abstract: Large Sediment Slump Reopens Unknown Scripps Submarine Canyon Tributary

Neil F. Marshall

A recent slump which developed during a storm introduced approximately 10⁵ cu m of sediment into the axis of Scripps Canyon, La Jolla, California. Slumps such as this are an important mechanism for the progressive downslope movement of sediment into the deeper ocean basins. This slump formed another head for the canyon approximately 400 m long, which cuts into unconsolidated shelf sediments to a depth of about 16 m. Exposed bedrock indicates that a canyon head existed there previously but had been filled and covered by recent deposits. Unique features were formed, such as secondary slumps perpendicular to the main slump trend with interspersed sharply peaked ridges.

After the event, the sediments within the slump valley were supersaturated and had little cohesion. They remained in this state for some time, finally approaching their previous state of stability after 6 months. The stability of the sediments on the shelf, even within 0.5 m of the scarps, remained unchanged from their preslump stability. A series of basin depressions along the valley floor suggests progressive slumping. Hydraulic "hammering," caused by large storm waves, is suggested as a mechanism for the initiation and headward advance on relatively low-grade slopes of shallow-water marine slumps.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA