ACTIVE GEOLOGICAL FAULTS AND LAND CHANGE IN SOUTHEASTERN LOUISIANA A Study of the Contribution of Faulting to Relative Subsidence Rates, Land Loss, and Resulting Effects on Flood Control, Navigation, Hurricane Protection and Coastal Restoration Projects Contract No. DACW 29-00-C-0034 July 2003 Cover: This diagrammatic north-south section, extending from Thibodaux, Louisiana to the Gulf of Mexico, depicts the subsurface geological processes which cause land submergence in Southeastern Louisiana. DISCLAIMER Some of the interpretations and results presented in this report may be controversial. This is to be expected, as the findings challenge a number of conventional concepts and basic assumptions. We recognize the far-reaching implications of these findings, and do not present them lightly. The authors have interpreted the data to the best of their ability, but are not infallible. It is assumed that the research community will rise to the challenge of testing new ideas that depart from convention. The maps and graphics in this report are not intended for zoning, property and insurance evaluations, engineering design, or similar purposes, but rather are intended to display scientific information. Site-specific geotechnical evaluations and risk assessments are recommended for all projects and land use evaluations within the study area ACTIVE GEOLOGICAL FAULTS AND LAND CHANGE IN SOUTHEASTERN LOUISIANA A Study of the Contribution of Faulting to Relative Subsidence Rates, Land Loss, and Resulting Effects on Flood Control, Navigation, Hurricane Protection and Coastal Restoration Projects Prepared by Sherwood M. Gagliano, Ph.D. E. Burton Kemp, III, M.S. Karen M. Wicker, Ph.D. and Kathleen S. Wiltenmuth, M.S., M.S. Coastal Environments, Inc. 1260 Main Street Baton Rouge, LA 70802 Prepared for U. S. Army Corps of Engineers, New Orleans District 7400 Leake Avenue New Orleans, LA 70118 Contract No. DACW 29-00-C-0034 July 2003 TABLE OF CONTENTS LIST OF FIGURES ...........................................................................................................vii LIST OF TABLES ............................................................................................................xix ACKNOWLEDGMENTS ................................................................................................xxi SUMMARY....................................................................................................................xxiii INTRODUCTION ...............................................................................................................1 FAULTS AND FAULT EVENTS.......................................................................................6 PREVIOUS RESEARCH..................................................................................................11 SUBSURFACE GEOLOGY .............................................................................................12 QUATERNARY DEPOSITS AND STRUCTURES ........................................................17 Displacement of the Pleistocene ....................................................................................17 Compaction of Holocene Sediments..............................................................................23 SURFACE EXPRESSIONS OF FAULTS ........................................................................24 Description, Evidence, and Mapping of Surface Faults ................................................28 Stream Alignments and Water Body Shapes .................................................................28 Case Studies of Surface Faults...........................................................................................43 SPECIAL STUDY AREAS ...............................................................................................45 Pontchartrain Basin........................................................................................................45 West Plaquemines Delta Plain (Empire and Bastian Bay Faults).............................................................................................................................54 Mudlumps ......................................................................................................................61 Delta Front Gravity Slumping ...................................................................................68 Continental Margin Gravity Slumping ......................................................................68 Middle Barataria Basin ..................................................................................................68 Terrebonne Delta Plain ..................................................................................................73 The Lake Boudreaux Fault (ET-1).............................................................................77 The Montegut Fault (ET-4)........................................................................................77 Isle de St. Jean Charles ..................................................................................................84 Fault severance of Bayou Terrebonne and opening of Lake Barré......................................................................................................................84 Correlation of apparent faults and land loss ..................................................................87 TRIGGERING MECHANISMS .......................................................................................87 Natural System Succession............................................................................................87 Stage 1. Delta Building: Prehistoric Times (Figure 59) ..............................................................................................................................91 Coastal Environments, Inc./20008 Page iii Stage 2. Poised: 1800 A.D. – 1850 A.D. (Figure 60) ..............................................................................................................................93 Stage 3. Early Deterioration: 1850 A.D. – 1900 A.D. (Figure 61).........................................................................................................94 Stage 4. Intermediate Deterioration: 1900 A.D. – 1950 A.D. (Figure 62)................................................................................................96 Stage 5. Advanced Deterioration: 1950 A.D. – 2000 A.D. (Figure 63)..............................................................................................98 Stage 6. Future: 2000 A.D. – 2050 A.D. (Figure 64). .............................................................................................................................99 Summary of Development Sequence.......................................................................101 Earthquakes and Seiches..............................................................................................103 Earthquakes..............................................................................................................103 Vacherie Fault Event (WM – 1)...............................................................................106 Other Reported Earthquakes ....................................................................................108 Seiches and Tsunamis ..............................................................................................109 Salt Water and Gas Migration along Fault Planes .......................................................110 Fluid Withdrawal.........................................................................................................112 VERTICAL AND LATERAL MOVEMENT.................................................................113 Relative Sea Level Rise ...............................................................................................113 Tide Gauge Data ......................................................................................................114 Sequential Land Leveling ........................................................................................120 NASA-Michoud Benchmarks..................................................................................120 Mississippi River Line - Chalmette to Venice.........................................................123 Bayou Lafourche Line .............................................................................................126 Bayou Petite Caillou Line........................................................................................129 Comparison of Mississippi River, Bayou Lafourche and Bayou Petite Caillou Lines................................................................................131 Vertical Movement and Rates of Subsidence and Relative Sea Level Rise for Epoch 2 .......................................................................131 Summary..................................................................................................................131 Other Processes Contributing to Land Loss and Coastal Erosion........................................................................................................138 Reduction of Overbank Flow and Sediment Supply................................................138 Reduction of Organic Matter Build-up and Deterioration of Floating Marshes ...........................................................................139 EFFECTS OF FAULTS...................................................................................................141 Effects on Wetlands .....................................................................................................141