Recent data from Archer et al. This style of hydrothermal activity is likely to be common in systems where the magma chamber has recently solidified allowing cooling and spreading to control the rate of downward crack propagation. Salty Dawg Field Located about 2 km north of the HRF near the center of the axial valley, Salty Dawg hosts more than 30 extinct or weakly venting, small sulfide structures covering an area of several hundred square meters. Chlorinities of the high-temperature fluids are the highest measured on the Endeavour Segment. Vigorous, high-temperature flow occurs mostly in the northern part of the field in which spectacularly tall and slender structures are characterized by numerous levels of large, overlapping sulfide flanges.
Fluids commonly escape through chimneys at the top of the structures and from the flange pools.
The boundary fault network that forms the western valley wall of the Endeavour Segment is the dominant structure localizing the . This vigorously active vent field is the locus of steep salinity and temperature gradients that cover an area about 400 m along strike and 150 m across strike. The field contains over 100 actively venting sulfide chimneys. All indications are that the MEF is in a period of active phase separation , and this affects all aspects of the chemistry. The fluids exiting the MEF bear the signatures of both supercritical and subcritical phase separation.