OVERVIEW of NeMO 2000 - Bob Embley

NeMO 2000 is the third expedition to the site of the 1998 eruption at Axial Volcano. This expedition has also been the most productive in terms of bottom time and efficiency. The lava flow area is still very active, but we have seen evidence at several sites on the '98 lava flow for a continued cooling off of the vents. However, since the caldera of Axial Volcano sits over a supply of magma delivered from deep within the earth, so it's likely that there will remain extensive active venting. Dives with the submersibles PISCES IV and ALVIN and the ROV ROPOS during the decade before the eruption revealed venting on the East Side and the ASHES vent field has been going on for at least 16 years (since its discovery). Although some of the biological communities were covered over with '98 lavas, their offspring continue to thrive in the new vents (how they colonize the new vents has been a focus of several studies on NeMO2000 (including a new study of larval dispersion by Anna Metaxas). It is clear from this years dives that the system has cooled down from the high level of activity in 1998 and the volcano may be returning to some baseline of activity. The temperature record obtained at the Cloud vent shows this particularly well. The suite of samples and measurements collected during the past three NeMO expeditions tell us much about the effects of the eruptions on the chemical and biologic systems but we also need to understand the state of the system between eruptions. The microbial community has been shown to be highly diverse during the past two years. Is this normal or was this diversity stimulated by the 1998 event? Do changes in the microbial and macrofaunal (e.g., tubeworms) communities correlate with changes in the chemistry of the hydrothermal system? How long will it be to the next eruption? Will there be signs of activity building before the eruption? For example, Hawaiian volcanoes gradually inflate (as in balloon) for a period of time preceding an eruption and then deflate when magma rises to the surface and is discharged. The deflation of Axial was measured by a pressure meter during the 1998 eruption and was about 10 feet. This year we've deployed a series of benchmarks and begun an annual program of precision depth measurements. These measurements, the bottom pressure meter placed in the center of the caldera, maintenance of the array of temperature sensors (MTRs and Hobo probes), and the annual suite of chemical an biological samples will continue to monitor the state of the volcano into the next cycle.

We have accomplished much on the three NeMO expeditions since 1998 but one of the key questions still remains. What happens during the first few hours to day of the event? Certainly, large quantities of heat and hot fluid are expelled from the seafloor during that period, but a response team has not yet arrived at a site on the Juan de Fuca Ridge soon enough to capture any of the initial fluids. The NeMO Net technology is a first step towards placement of an autonomous event response system on Axial. In 2001, we will place a chemical sampling and sensing system (probably at Cloud vent) that will send realtime chemical data back to shore. If there is an unusual event, the sampler can also be activated to recover samples for later analysis. In succeeding years, we plan to add a remote-controlled water column sampling system and dock an autonomous vehicle within the caldera.

The scientific party is grateful to the ROPOS group and the personnel of the Ronald H. Brown that has made this expedition a great success.