University of Oregon
The Volcano is active! Large plumes continuously billow up from Brimstone Pit. Plumes carry CO2 bubbles and ash particles. (click image for full size)
As the time approached for our first Jason dive, the anticipation in the air became palpable. We had been preparing for this dive for two years, and during this time had been monitoring the volcano’s activity through glimpses provided by other cruises in the area. In February 2008, a hydrophone and plume sensor were deployed on a mooring at the summit of NW Rota-1 volcano, with the help of the US Coast Guard ship Sequoia. The mooring stayed down for a year and was retrieved in February 2009. The data from both the hydrophone and plume sensor clearly showed that the volcano had been very active from February through August 2008 and less active from August through February 2009.
Ash from plume after a large burst of activity, covers the basket of instruments in front of ROV Jason.
Our first Jason dive confirmed the previous day’s evidence from the CTD survey that Brimstone Pit, the active eruptive vent, is still active and well named. It sits southwest of, and slightly below, the volcano’s summit and is currently at a depth of 522 m below sea level, almost 40 m higher than it was when we last visited it three years ago. The vent is about 2 m across and formed by a loose pile of lava blocks. It appears to be continuously active, emitting billowing ‘clouds’, large bubbles of gas, and an episodic rain of small lava fragments. Unlike volcanic plumes on land, however, the ‘clouds’ are not formed of steam but instead are composed of tiny dispersed droplets of molten sulfur, or brimstone, an ancient name for sulfur. The bubbles are filled with CO2, all that remains of the magmatic gas after the original water and sulfur have condensed to liquid (water) or solid (sulfur) phases. The lava fragments provide hints of what is happening in the vent, behind the curtain of sulfur clouds.
My personal reaction to my first glimpse of Brimstone Pit was not only excitement but also amazement and awe. I am a volcanologist who has spent my career traveling the world to study active volcanoes. But this was my first experience with a volcano erupting under the ocean – an ocean that on the surface, looks unremarkable, with no hint of what is happening below. My reaction was to try to understand the activity that I was seeing on the video monitors by comparing it with volcanoes that I have studied on land, particularly the volcano Stromboli in Italy, which is also perpetually active.
'Within the 'smoke', many gas bubbles of CO2 can be seen. Typically after bubbles appear, activity at Brimstone would increase, actually shaking the ROV. (click image for full size)
Thus, our first glimpse of Brimstone Pit on this trip shows a volcano in continuous activity, with a vent that has built to a height almost equal to the volcano’s summit and producing a eruption plume composed primarily of particulate sulfur, CO2 bubbles and lava fragments. How representative is this snapshot of the volcano’s normal range of eruptive activity? We’ll find out over the next few weeks!
Volcano Observation Videos:
All video copyright by Advanced Imaging and Visualization Lab WHOI
White billowing eruptive plume full of sulfur and ash coming out of Brimstone vent (no audio).
Clear bubbles rising from the eruptive vent are mainly CO2, while the white cloud is dominated by sulfur from SO2 (no audio).