March 13, 2001 to June 2, 2001
Monterey to Hawaii and back
April 24, 2001: Leg 3; Day 4
Dave Clague writes: After leaving the Kohala plunge pools about breakfast time after a night dive, we steamed for Puna Ridge, the submarine portion of Kilauea Volcano's east rift zone. The transit is almost directly into the trade winds and swells, so we did not arrive at the dive site until several hours after lunch. The dive explored a region of the rift zone between about 2200 and 2000 m depth. This region is the inferred location where some very unusual high-temperature lavas erupted in the past. Their existence is documented only by some glass sand grains recovered in a core. These lavas erupted at temperatures of about 1325 degrees centigrade-nearly 165 degrees hotter than typical lava at Kilauea. No historic eruption has erupted such lava and we do not know what the lava flows might look like. The dive explored a series of volcanic cones in the area, but did not find any highly fluid lava, as might be expected for such hot lavas.
We found a number of exciting volcanic features including the submarine equivalent of shelly pahoehoe, a thin slabby type of flow found near eruptive vents on land. The submarine near-vent lavas are hollow pillows (some "eggshell pillows") with thin rinds and some sheet-like flows. We also found a collapse pit that had been a lava pond and had several lava tubes exiting the pit, some lava pillars, and numerous fine-scale lava pond levels recorded as "bathtub rings". Some of the volcanic cones are unusual in having nearly vertical walls of truncated pillows above extensive slopes of talus that consists of the pillow fragments. The walls are so sharply defined that they at first appear to be fault scarps, but we think they are constructional steep pillow ridges, modified by mass wasting. All the lava flows seen are relatively old, having heavy palagonite alteration of the glass rinds. Several areas were partly buried in black glassy volcanic sands, which may be from nearby younger eruptions. Although the primary objective-to find the high-temperature lavas-was apparently not accomplished, the dive observations and samples will lead to better understanding of submarine volcanic landforms.