Naruse, Hajime1, Yu
Saito1, Fujio Masuda2 (1)
As an initiation mechanism for turbidity currents, the flow transformation of debris flows has been suggested to be significant. Our study aims to investigate behavior of subaerial debris-flows transiting into subaqueous environments. For that purpose, we conducted flume experiments, and observed internal velocity field of the transforming debris-flows by using particle image velocimetry (PIV) method. As a result, clear transition from laminar debris-flow into turbulent flow was identified, and our experiments implies that bipartite or tripartite turbidite exhibiting evidences of multiple surging may also be produced by flow transformation of a single debris-flow.
Experimental procedures are following: Water filled an experimental flume (60 x 200 x 8 cm) up to 30 cm in depth. Sand, clay and water was mixed, where sediment concentration was 65-75 w.%. Then, sediment/water mixture flowed as a debris-flow on the slope inclined 10-40 degree in the flume. Visual representation of the experimental flow observed by using the high-speed camera was examined by the PIV method.
On the basis of investigation of velocity field, the transforming debris-flow can be subdivided into the two parts: the turbulent head and 2-layered (turbulent and laminar) body. With contrast to the fully turbulent state of the flow head, the body is 2-layered flow where lower part is laminar and upper part is turbulent. Velocity field investigation by PIV illustrates that boundary between 2-layers in the flow body shows wavy form which is probably attributed to K-H pillows. Transition from the head to body is rapid and drastic, so that the difference in downcurrent velocity between two parts finally causes detachment of the flow head, producing discrete surges of the turbidity current from a debris-flow.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California