This figure compares hydrothermal plumes overlying the 1998 eruption zone as mapped in July 2000 and July 2001. The heavy red line marks the approximate extent of the main 1998 lava flow. "NTU" is a measure of the relative concentration of particles suspended in the plume; higher values indicate a higher concentration of hydrothermal material. The figure shows that relative to 2000, the plumes this year are less extensive, of lower concentration, and have a lower height of rise above the seafloor. All these signs point to a lessening of hydrothermal activity.

R/V Wecoma - CTD Cruise
Science News

Science Report - Tuesday, July 24, 2001
Position - 45 54.659' N /130 12.053' W
Chief Scientist Ed Baker

We are finding some time now to think about the data we're collecting and compare it to previous year's results. The accompanying figure shows results from two CTD tow-yos along the trend of the 1998 volcanic eruption on the east side of the caldera. Compared to last summer, this year's tow shows that hydrothermal plumes extend over less of the eruption site, have weaker concentrations of hydrothermal particles, and a lower height of rise above the seafloor. We interpret these observations to indicate that there are fewer active sites of fluid discharge because the lava below the seafloor continues to cool and provide less energy for hydrothermal circulation in the crustal rocks. In addition, the lower rise height suggests that the temperture of the fluids still being discharged is cooler than before, just like a smouldering fire generates a shorter plume of smoke than a blazing campfire. Very hot hydrothermal fluids, with temperatures around 350C, typically rise some 200-300 m above the seafloor. The present rise height of the plumes here is about 100-150 m, and has been decreasing each year since 1998.

We will be finishing up our work here in next day or two and will try and summarize what we have learned on our visit to Axial Volcano this year. Then we will be steaming southward to the Cleft segment of the Juan de Fuca Ridge, where we have been observing hydrothermal plumes every year since an eruption there in 1986.