Mud Volcanoes from the Beaufort Sea to the South China Sea

Abstract:

The detailed morphology of five submarine mud volcanoes were surveyed using an Autonomous Underwater Vehicle (AUV) developed at the Monterey Bay Aquarium Research Institute. Mud volcanoes are constructional features built by extrusion of gas, subsurface fluids and fine-grained sediment. Two surveys covering four submarine mud volcanoes were conducted on the CCGS Sir Wilfred Laurier in the Beaufort Sea in the Canadian Arctic. A survey of one mud volcano was conducted on the Taiwanese Ocean Research V in the South China Sea, SE of Taiwan. The AUV carried a multibeam sonar, a 1-6 kHz chirp sub-bottom profiler, and a110 kHz sidescan, and obtained overlapping multibeam bathymetric coverage at a vertical resolution of 0.15 m with a horizontal footprint of 0.9 m and chirp seismic-reflection profiles with a vertical resolution of 0.11 m. Mud volcanoes were either flat topped or conical. The conical mud volcano off Taiwan had a diameter of ~2 km and 10° side slopes; the conical feature in the Beaufort Sea had a diameter of ~1.5 km and 4° side slopes. The sides of the conical mud volcanoes were smooth, suggesting they were formed by sediment flows that emanate from a vent on their crests. The flanks of the conical mud volcanoes characteristically had very low acoustic reflectivity, but one single high reflectivity trail from the crest of the Beaufort Sea mud volcano indicates a recent flow. Three mud volcanoes in the Beaufort Sea formed circular, flat-topped plateaus that are up to ~1.1 km in diameter and elevated up to 30 m from the surrounding seafloor. The fine scale morphology and reflectivity on these plateaus show low relief, concentric, and ovoid circles that appear to be mud boils probably associated with eruptive events of varying ages at shifting vent sites. The different mud volcano shapes are attributed to variations in the viscosity of the erupting sediment slurries and may represent a sequential morphology, which is altered by shifts in venting position over time.