SHORT- AND LONG- TERM MOVEMENT OF MUDFLOWS AT SOUTHWEST PASS ON THE MISSISSIPPI RIVER DELTA FRONT: AN UPDATE

Submarine mudflows are a complex and poorly understood phenomenon that pose a threat to seabed infrastructure in the Northern Gulf of Mexico (NGoM). Historically, research was focused on understanding the causes of large-scale hurricane-related seabed failures due to their impacts on oil and gas platforms and the 1000’s of kms of pipelines across the Mississippi River Delta Front (MRDF). Recently, work investigating non-hurricane forced sediment displacement has attempted to quantify how episodic to progressive movement of smaller sediment volumes shape the MRDF region and contribute to local geohazards. To that end, this research analyses repeat bathymetric and sidescan sonar surveys of Southwest Pass (SP) on the western side of the MRDF in the years 2016, 2017, 2022, and 2023 to distinguish indicators of relatively slow, but seemingly continuous fair-weather creep of the mudflows (between 2016 – 2017 and 2022 – 2023), and potentially more punctuated movement triggered by large-scale storm activity in the Northern Gulf of Mexico (between 2017 – 2022). Time series analysis tracking the locations of discrete sedimentary blocks within SP mudflow gullies illustrate a positive correlation between periods of relatively higher storm intensity and increased annual average block motion. Our results identified average block motion of ~ 6.5 m/y during the 2016-2017 analysis period, which coincided with relatively limited NGoM storm activity (<2 hurricanes), and ~12.7 m/y during the 2017-2022 analysis period, during which four 2020 hurricanes made landfall in Louisiana.