USGS - science for a changing world

St. Petersburg Coastal and Marine Science Center

St. Petersburg Coastal and Marine Science Center > Subsidence and Fault Activation Project > Presentation

Recent Reductions of Subsidence Rates in the Mississippi River Delta Plain

by Robert A. Morton1, Julie C. Bernier2

Abstract

PowerPoint Presentation: download the presentation in PowerPoint format

PowerPoint Presentation - 7.5 MB PPT

Download the PowerPoint version of the slide show.

The Mississippi River delta plain has long been characterized as an area with high rates of relative sea-level rise. This concept was tested by integrating National Ocean Service tide gauge records with National Geodetic Survey benchmark releveling data and GPS elevations at Continuously Operating Reference Stations, providing a basis for understanding historical subsidence trends and most recent rates for southeastern coastal Louisiana. Tide gauge records indicate that rates of relative sea-level rise at Grand Isle accelerated from about -2.2 mm/yr between 1947 and 1964 to about -11.5 mm/yr between 1964 and 1991 and then decelerated to about -3.4 mm/yr between 1991 and 2006. These trends and rates are independently verified by repeat leveling surveys that yielded an average subsidence rate of -9.6 mm/yr from 1965 to 1993 at benchmarks between Leeville and Grand Isle and GPS-derived elevation changes at Cocodrie that yielded an average subsidence rate of -4.4 mm/yr from 2003 to 2005. The most recent slow rates of subsidence are similar to those averaged over geological time scales (e.g., radiocarbon-dated peats) that are attributed to natural sediment compaction and crustal loading.

The historical pattern of slow, then rapid, then slow subsidence may be caused by natural deep-basin processes (e.g., faulting, salt migration) but is more likely related to regional hydrocarbon production that followed the same general temporal trends. If accelerated subsidence was induced by reservoir compaction and fault reactivation associated with fluid withdrawal that also accelerated in the 1960s and 1970s, then the most recent reductions in subsidence rates likely reflect a balancing of subsurface stresses and a return to near-equilibrium conditions. Understanding historical and current trends in subsidence rates and their causes is critical for designing and successfully implementing coastal-restoration activities and for modeling and predicting expected impacts of relative sea-level rise on the delta plain.

1U.S. Geological Survey, FISC, Austin, TX
2U.S. Geological Survey, FISC, St. Petersburg, FL

Additional information and supporting documents can be found at http://coastal.er.usgs.gov/gc-subsidence/.

Note: you will need Microsoft PowerPoint to view the PowerPoint version.

Can't view the PowerPoint version of the presentaion? Read the plain text version (9.3 KB).


Related Research Project:

Subsidence and Fault Activation Related to Fluid Energy Production, Gulf Coast Basin Project
USGS Coastal & Marine Geology Program


St. Petersburg Coastal and Marine Science Center > Subsidence and Fault Activation Project > Presentation

Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL:
Page Contact Information:
Page Last Modified: