Logbook: September 2, 2006

Position: 45°56.0’N, 129°59.0’W
Axial Volcano

Taking a measurement with the pressure sensor (yellow cylinder) on a benchmark (triangular platform) on the 1998 lava flow. The pressure data gives us the depth of the benchmark to within 1 cm. (click image for larger view)

During ROPOS dive R1010 a few days ago we repeated precise pressure measurements at an array of points on the seafloor in order to monitor inflation of Axial volcano. The last measurements we made were two years ago and this year’s data show that the center of the caldera has uplifted by 21 cm (~8 inches) since 2004. This continues a trend we have documented since the 1998 eruption, although the rate of uplift appears to be slowing. We estimate the caldera has now risen a total of 1.7 meters (~5.5 feet) since the 1998 eruption. The uplift is caused by magma accumulating in a reservoir located beneath the caldera. Eventually, this refilling will lead to Axial’s next eruption and we hope these measurements may help forecast when that will occur. During dive R1010, ROPOS also recovered and replaced long-term temperature recorders at hydrothermal vents distributed throughout the caldera, another part of our long-term monitoring effort at Axial.

Today, ROPOS dive R1012 made several geologic traverses across the 1998 lava flow to document the distribution of lava pillars. These unusual-looking spires are hollow pipes that connect the upper and lower crusts of the lava flow when the interior of the flow is still molten. The pillars are visible at the edges of collapse areas that form when the molten interior drains and the upper crust caves in. ROPOS collected several samples of the pillars for chemical analysis. We also discovered for the first time that small hydrothermal clams have now colonized some vents on the 1998 lava flow. During our traverses, we also discovered some new vent areas, like Zen Garden, that we had not run across before.

At the end of dive R1012, ROPOS recovered a monitoring instrument that had been deployed right after the 1998 eruption (a “rumbleometer”, like the one that got stuck in the 1998 lava flow). The batteries in the acoustic release were dead, so the only way to get it back was to physically haul it up to the surface, but since it still had its anchor attached it weighed 500 pounds in water and 1600 pounds in air! That’s a heavy load - and before this year - too heavy for any ROV to manage. But ROPOS’s new configuration allows it to lift loads up to 4000 pounds, so we decided to try out this new capability. ROPOS clipped a hook into the instrument and gently lifted it off the seafloor, suspended by a line below the vehicle. The whole operation went incredibly smoothly and was very impressive!