Science Report:
While we are collecting data along the Cleft segment we have been catching up on the data we collected several days ago at Axial Volcano. Since we will be returning there in a few days we wanted to think about what we've learned so far in order to better plan our remaining time at Axial. As an example of what we've been thinking about I've included images of two CTD tow-yos we conducted along the axis of the 1998 lava eruption at the summit of the volcano.

The top image shows the hydrothermal plume as we mapped it in 1999. The colors indicate the concentration of hydrothermal particles suspended in the water. Red colors mean more particles and blue colors less. As you can see, there was an intense plume directly over the eruption site in 1999, and this plume extended for several kilometers away from its source-the new hydrothermal field created by the eruption. Also, the plume rose almost 200 m above the seafloor. Plumes act somewhat like hot air balloons-the hotter the vent water and the greater the discharge volume, the higher a plume will rise through the cold seawater. Some plumes from very vigorous vent fields rise more than 1000 m above the seafloor!

The second image is a tow we did a few days ago along the same track line. As you can see, this year the plume is much less intense and is not as widely distributed as last year. Also, the plume rises only about 100 m above the vent field. This much smaller rise height indicates the discharge and temperature of vent fluids have decreased substantially in the past year. When we return to Axial, we will map this plume in more detail in order to create a 3-D picture of the plume over the volcano summit. From these data we will be able to more accurately estimate how much the venting has changed since the 1998 eruption.