Getting Gas

Collecting Bubbles Under Pressure

Capturing bubbles using an ordinary funnel placed over the gas sampler's intake.

Leigh Evans
Oregon State University

As the 'Fire and Brimstone' blog entry showed, Brimstone Pit releases streams of gas bubbles that are composed mostly of carbon dioxide. They and the fluids they rode in on, can be captured with titanium "gas tight bottles." These specially designed bottles can withstand the pressures of all currently workable ocean depths both from within and without. At the depth of NW Rota-1, gas bubbles should be at a pressure about 60 times atmospheric. The version of the gas tight bottle that catches gas bubbles is outfitted with a kitchen funnel, a rubber stopper, thin plastic tubing and some glue. One hydraulic "arm" of Jason II includes a special hydraulic ram to push the triggering button of the gastight bottle. All we need to do is position the funnel to catch bubbles and trigger the bottle at the appropriate time.

Brimstone's gas bubbles are primarily composed of CO2(90%).

The PMEL Helium Isotope Lab has gathered fluid and separate CO2 rich phases from six volcanoes; four on the Mariana Arc and two on the Kermadec/Tonga Arc. In all but one volcano, the separate phase is gas bubbles. Comparison of the measured concentrations of helium and carbon dioxide to those based on published solubilities revealed that the fluids contained far less gas than one would expect if the bubbles had been the product of the fluid degassing its dissolved contents. It appears that the “extra” gas is coming directly from magma inside these volcanoes, or in the case of NW Rota-1 directly from lava erupting at the surface. In some cases, sub-surface boiling might also be involved. We are collecting additional samples on this trip to try to figure this puzzle.

A funnel attached to a “gas-tight” sampler is used to collect gas bubbles rising from the eruptive vent. (no audio)
All video copyright by Advanced Imaging and Visualization Lab WHOI