Analysis of Past and Future Debris Flows and Turbidity Currents Generated by Slope Failures Along the Sigsbee Escarpment in the Deep Gulf of Mexico
Authors: Niedoroda Alan W. , Reed Christopher W. , Hatchett Lyle , Young Alan , Lanier Dan , Kasch Vernon , Jeanjean Philippe , Orange Dan , Bryant William 
Published: October 2008

There are many seafloor features on and near the base of the Sigsbee Escarpment that were formed as the result of mass gravity flows. Accordingly, a multidisciplinary team conducted an evaluation of these features as part of an overall study of geohazards. The goals of these evaluations were to:catalog the varieties of mass gravity flows that have occurred in the past,understand the causes of these events,characterize the kinematics (e.g., speeds, dimensions) of these flows, andportray the relative magnitudes of the spatially dependent exposures to possible future events.

To accomplish these goals, there was extensive use of previously collected seismic exploration data that included seafloor bathymetric images and shallow reflection amplitudes. Maps of mass gravity flow features, sources, and flow paths were developed. These were used to plan a comprehensive program of bottom surveying with an autonomous underwater vehicle (AUV). The fieldwork also included a program of navigated deep piston-cores and box cores, along with video observations from an ROV. One goal of the field program was to acquire adequate data to characterize seafloor mass gravity flow features and deposits. These were used as inputs and "targets" for numerical modeling to simulate the features. The approach is that properly detailed mathematical representations of the physics of mass gravity flows are used to "backcast" the behaviors and flow kinematics of the events that caused the observed features. This provides model calibration, which allows the model to be applied in a prognostic mode.

Sediments were described and analyzed for grain size, erodibility and age. Geophysical data were reduced and archived in a GIS system. Numerical models of debris flow, mudflows and turbidity currents were applied.

The results show that several types and scales of mass gravity flows (debris flows and turbidity currents) have been active all along the portion of the Sigsbee Escarpment covered by the surveys. The scale and form of these features are localized and predictable. Representative flow kinematics were determined for each of the flow types using the results of the fieldwork and modeling. Activity of these features diminished markedly over the past 10,000 years as sea level rose following the last ice age.

Introduction

One component of a multi-faceted examination of potential geohazards in the Atlantis and Mad Dog prospect areas along and below the Sigsbee Escarpment has been directed at understanding mass gravity flow activity. In principle, an understanding of past activity is a necessary step in developing the capability to forecast future activity. The goals of the evaluation were to:catalog the varieties of mass gravity flows that have occurred in the past,understand the causes of these events,characterize the kinematics (e.g., speeds, dimensions) of these flows, andportray the relative magnitudes of the spatially dependent exposures to possible future events.