Holocene Evolution of the Galveston Bay Punctuated by Rapid, Episodic Changes: Implications for Future Change

Using seismic data and sediment cores collected within Galveston, we have been able to reconstruct the bay's evolution with considerable detail. These data show that Galveston Bay has had a history of rapid and dramatic change, in response to sea level rise across the irregular topography of the old river valleys and changes in climate that regulated sediment supply to the bay. In general, the valley morphology consists of a deep incision near the center and broad, terraced flanks. As sea level rose during the Holocene the bay changed from a narrow, deep bay to a wide, rounded bay as the valley was flooded. As sea level rose to the elevation of relatively flat fluvial terraces these areas were flooded rapidly, resulting in expansions in bay area of up to 30% and dramatic re-organization of bay environments. The most notably changes were up-valley shifts in the bayhead delta of tens of kilometers. These events took place within a century or two. The most dramatic flooding events took place at approximately 9,600, 8,900, 8,500 to 8,200, and 7,300 to 7,100 cal. Yrs BP. These events were caused by a combination of rapid sea level rise, flooding of low antecedent topography and decreases in sediment supply. Changes in sediment supply were caused by climate change and changes in the area of the bay, which resulted in increased sediment accommodation and associated decreases in sedimentation rates. Anthropogenic changes is sediment supply, by construction of dams, and accelerated subsidence due to groundwater and hydrocarbon extraction, are occurring at rates that equal those that caused past rapid flooding events. It is possible that the response of these recent changes have yet to take place.