Shallow-water gaseohydrothermal plume studies after massive eruption at Panarea, Aeolian Islands, Italy

Abstract

Marine water dynamics in the near field of a massive gas eruption near Panarea (Aeolian Islands volcanic arc, SE Tyrrhenian Sea) is described. ADCP current-meters were deployed during the paroxysmal phase in 2002 and 2003 a few meters from the degassing vent, recording day-long timeseries. Datasets were sorted to remove errors and select good quality ensembles over the entire water column. Standard deviation of error velocity was considered a proxy for inhomogeneous velocity fields over beams. Timeseries intervals had been selected when the basic ADCP assumptions were fulfilled and random errors minimized. Backscatter data were also processed to identify bubbles in the water column with the aim of locating bubble-free ensembles. Reliable timeseries are selected combining these data. Two possible scenarios have been described: firstly, a high dynamic situation with visible surface diverging rings of waves, entrainment on the lower part of the gas column, detrainment in the upper part and a stagnation line (SL) at mid depth where currents were close to zero and most of the gas bubbles spread laterally; secondly, a lower dynamic situation with water entraining into the gas plume at all depths and no surface rings of diverging waves. Reasons for these different dynamics may be ascribed to changes in gas fluxes (one order of magnitude higher in 2002). Description of SL is important to quantify its position in the water column and timing for entrainment-detrainment, and it can be measured by ADCP and calculated from models.

Cyclic Behavior Associated with the Degassing Process at the Shallow Submarine Volcano Tagoro, Canary Islands, Spain

“…Hydrothermal vents have been studied in terms of fluid geochemistry characterization, physical-chemical processes [3,12,13], and biological communities [14]. Fewer studies have been carried out on the water dynamics in the near field of hydrothermal vents [13,15,16]. Water dynamics can change with the intensity of the flux of fluids and with seismic activity in the area [17].…”

“…At shallow depths, vent plumes are usually small [19]. Moreover, in these areas, where hydrostatic pressure is not the major force controlling gas dilution and water boiling, vents are of the hydrothermal type, with high flow rates of free gas, principally CO 2 , and many diffusive and sparse columns of gas bubbles are frequent [15,16,20,21].…”

Intense but variable autotrophic activity in a rapidly flushed shallow‐water hydrothermal plume (Kueishantao Islet, Taiwan)

“…In contrast, the background seawater is far away from the influence of the vents. The ambient water indeed is a mixture of background seawater with previously formed plume water (“former plume water” hereafter) due to turbulent mixing in the surface ocean and the plume entrainment‐detrainment processes (e.g., Tudino et al., 2014). Due to dilution, the Si(OH) 4 concentrations used to calculate the vent‐fluid component in the background seawater and ambient water were indistinguishable.…”

Submarine vortices derived from natural gas hydrate conversion: a mechanism for ocean mixing

“…Undirected hydrostatic pressures decrease during bubble ascent resulting in gas exsolution and bubble expansion and fragmentation, which in turn results in increased buoyancy, possible expansion of the bubble plume, and changes in the interfacial tension of hydrate-shelled bubbles. Vortex tube generation could explain the consistent relatively slender morphologies associated with plumes seen in multibeam data (Solomon et al, 2009;Colbo et al, 2014;Skarke et al, 2014;Smith et al, 2014;Tudino et al, 2014;Weber et al, 2014;Garcia-Pineda et al, 2015;Wilson et al, 2015) and recent observations indicate that vertical rise of buoyant plumes may be augmented by spiral flow geometries (von Deimling et al, 2015). Because the reflection and scattering from a bubble plume is a bulk effect, rotation has not been observed in seismic reflection data.…”