Monterey Bay Aquarium Research Institute

Hawaii Cruise
March 13, 2001 to June 2, 2001
Monterey to Hawaii and back

April 24, 2001: Leg 3; Day 4

These elongate pillow lavas flowed down a steep slope.

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.

These gorgonians are presumably taking advantage of this lava mound to get higher in the water column for more food.

The density of animals was greater at Puna Ridge than anywhere else we have dived in Hawaii so far. This forest of gorgonians was remarkable.

This is a lava pillow that drained and cracked open. The rinds of these pillows have weathered somewhat, but still display the original texture from when they squeezed out and chilled.

This interesting sponge is growing on a lava sheet flow. High temperature lavas would be less viscous than lower temperature ones, so might be expected to erupt as sheet flows rather than as pillows. Glassy volcanic sand, like which makes up black sand beaches on land, fills the hollows.

This is a skylight, a break in the roof of a lava tube. Once a lava flow tubes over, it can travel long distances because it stays hot, insulated within the tube. On land, you can stand next to a skylight, peer in, and see the molten lava flowing like a red torrent below.

This is the submarine equivalent of "shelly pahoehoe". On land, the crusts of thin sheet flows break easily under foot. The surface is crunchy to walk on, and if it is hollow underneath you risk breaking through and tearing up your shins. Gorgonians have found the surface here quite to their liking.

These elongate pillows formed "pillow toes": as the lava lobe chills, it might briefly remain hotter where it contacts rock underneath, which causes it to curl upward before stopping. We saw this happen a week ago on Kilauea.


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