Science
Report:
We arrived at
Axial Volcano yesterday and immediately began recovering instruments on
the seafloor that we had left during last year's cruise. Since we can
only visit Axial with a ship once a year, we must depend on instruments
to provide information on changing hydrothermal conditions between cruises.
Last year we deployed nine moorings around the volcano. The moorings are
lengths of special line 200 to 500 m long, anchored at the bottom with
a heavy weight and held upright by several floats attached at the top
and bottom. Old railroad wheels are commonly used as weights, and the
floats are hollow glass balls about one-half meter in diameter. At the
bottom of each mooring is an acoustic release. When it's time to recover
the mooring we send a coded acoustic (sound) signal from the ship to the
release, which trips a lever that disengages it from the weight and allows
the entire mooring to float to the surface. We borrowed this idea from
marine mammals such as whales and dolphins, which use similar acoustic
signals to communicate with each other. Our acoustic signals sound like
a rapid series of high-pitched "pings." We can't use radio or light to
communicate because these electromagnetic signals can travel only a short
way through water, while sound waves can be heard for great distances.
On the moorings we have
three kinds of sensors. Temperature sensors monitor the changing temperature
of the seawater. Optical sensors monitor the amount of particles in the
water by shining a light into the water and measuring how much is reflected
back from the tiny particles suspended in the water. These particles are
created when the hot hydrothermal fluids mix with the cold seawater. Current
meters measure both the speed and direction of water movements. By combining
all three of these measurements we try and reconstruct the movement of
hydrothermal plumes during the time the moorings were on the seafloor.
Our first day of mooring
work has been highly successful. We sent acoustic signals to three releases
and each mooring returned safely to the surface. It then takes some delicate
ship handling to drive a 300-foot ship close enough to the floats for
us to grab them with a boat hook while not running right over them! The
crew on the bridge did a great job and we pulled all three moorings and
their instruments back on board.
Our next task is to get
the sampling gear ready for our first opportunity to sample the hydrothermal
plumes since last year. We're all wondering how the hydrothermal activity
has changed over a year.
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