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May 18th, 2003; Leg 6, Day #4 Addendum

(Click images for larger view.)

The datalogger from the thermocouple array has been downloaded to reveal the temperatures found within the growing chimney at Busted Mushroom. An example time series here, recorded from March 7 to March 27, shows the growth of the chimney wall over 20 days. All but one of the thermocouples became embedded in the chimney wall within a few hours. All but three of the thermocouples remained within the central channel. Of the other three, one was outside the chimney wall (blue line), while two became embedded within the wall (green and light blue lines). The temperatures within the wall dropped slowly (as shown by the green line) as the wall thickened and became less permeable. 

0518_wall1.jpg (37381 bytes)

The thermocouple outside the wall (dark blue line) did not reach such high temperatures. The red line shows the temperature recorded back within the thermocouple casing, located a few feet from the chimney. The periodic variability shown in the records from the outer thermocouple and from one the thermocouples located within the wall (light blue line) may be related to pressure changes caused by tidal currents in the vent area. The pressure changes could cause periodic changes in advection rates of cold fluid into the wall, resulting in the records shown. Similar temperature variability within growing chimneys has been attributed to this at other vent sites, and provides evidence for walls being very permeable. In the lower figure, we have expanded the record for the first few days after the thermocouple was inserted into the broken chimney on March 7, 2003.

0518_wall2.jpg (33496 bytes)

Meg Tivey and Debra Stakes

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