At 1933 PST July 26, 2015 after descending ~1840 m beneath the oceans surface, the remotely operated vehicle ROPOS and the University of Washington Ocean Observatories Initiative Cabled Array team set first eyes on the April 24th, 2015 voluminous eruption of Axial Seamount. The vehicle landed within 10 m of the toe of the new flow, and within two minutes fresh bulbous pillow flows on top of older flows were encountered.
From the base of the most northeast lobe of the eruption, ROPOS ascended 90 m (295 ft) up the face of the flow to the summit, which reaches 670 m across. Glassy pillow flows, some more that a meter across and several meters in length cascade down the 30° slope. Cabled Array hydrophones detected acoustic signals reminiscent of explosions during the eruption. Although a few pillow fronts were highly fragmented, these were rare in occurrence on this lobe of the flow.
Upon reaching the summit, ROPOS was engulfed by a blizzard of flocculant material and cloudy water. Methane and sulfur-utilizing organisms, thriving within voids beneath the new lava flow, likely generate this material. A gridded traverse of the area was conducted, but no large snowblowers were seen similar to what was observed during the 2011 eruption. Instead it appears that the floc is from small numerous diffuse flow sites hosting bacterial growth within localized hollows between individual pillows. The highest fluid temperatures, up to 18°C, were measured in diffuse flow issuing from white filamentous bacterial mats surrounded by orange mats. Perhaps most impressive are thick orange mats of bacteria that completely coat broad expanses of this three month old flow. The mats are prevelant on the summit of the flow in areas where moderate sized collapse zones are present – one such area had significant egress of clear fluids issuing from it.
The April 24th eruption was detected in real-time by seismometers, pressure-tilt instruments, and hydrophones on the summit of the volcano as part of the OOI Cabled Array. Indeed, over an ~24 hr period, the instruments streaming live data back to shore detected ~8000 earthquakes and a drop in the seafloor of 2.4 m. In total, the flow extends for ~ 7 km along the northern rift of Axial Seamount.
This exploration dive occurred while the OOI Cabled Array team was preparing a Deep Profiler Mooring for installation at the base of Axial Seamount. The team is also performing scheduled maintenance on other instrumentation and platforms that were installed in 2014.
It was a fantastic dive and the team is very greatful to the National Science Foundation and the OOI program for this opportunity.