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In some
hydrothermal vent areas and under certain temperature and pressure conditions
the vent fluid actually boils beneath or at the seafloor. When this happens,
the vent fluid may separate into two distinct phases, a vapor phase and
a brine phase. Dissolved gases are concentrated in the vapor phase, whereas
the dissolved metals are concentrated in the brine phase. Such phase separation
is on-going in the ASHES vent field at Axial. At ASHES, the vapor and
brine phases come out in different areas of the vent field and they produce
very different chimneys. Vapor phase chimneys, like Virgin mound, are
composed almost entirely of anhydrite and are very fragile. On the other
hand, brine-phase chimneys, like Inferno vent, are larger and stronger
because they are composed of metallic sulfides. The flame-like flickering
at Inferno vent is caused by light reflecting off bubbles forming and
collapsing in the vent fluid - more evidence of phase separation. At the
base of Castle vent there is also an active anhydrite chimney.
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