Velocity
Structure of Subaerial Debris Flows Transforming into
Tubidity Currents
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