Several highly successful dives on the submerged reefs on Mahukona
Volcano in the past several days opened up the opportunity to revisit our
second refuge from the vigorous trade winds, the South Kona area. We
steamed southward overnight to carry out the longest dive (15 hrs) with
the highest climb (1250 meters) of the leg. We also collected the
heaviest, and the most rocks, a total of 35 samples; problem is, now we
have to describe them! Starting at 3250-meter water depth, we traversed a
series of slump blocks along the northern seaward edge of the South Kona
Landslide, just south of the margin of the Alika debris slide that we
explored previously. Not surprisingly, we found massive cliffs of broken,
volcaniclastic sandstones and breccias. To our surprise, many of the
sediments were very fine-grained, unlike fragmental basalts one usually
sees in volcanic settings. We now have to explain why. Much of the outcrop
was highly sheared and fractured. We now think we can pick several major
fault zones, formed when the blocks tore loose during catastrophic
collapse of the southeastern flank of Mauna Loa. Fractures on the broken
rock surfaces sometimes defined a "jig-saw puzzle" texture.
Elsewhere, submarine erosion left dramatically sculpted chutes and
gullies.
A "family" of tripod fish provided us with relief from the
massive cliffs of broken rock that made up much of this dive. They stand
out, because they prop themselves up on 3 long fins, standing nearly a
meter high. We ran into these unusual fish at least 4 times during the
dive!! Sometimes they were found in pairs, other times towering above
their close relative, the spiderfish, perched on slightly shorter fins. A
colorful sea urchin proved to be the owner of a furrowed terrace we
crossed along the way. We also encountered several sea cucumbers, and a
bizarre, unidentified animal with a big "tongue" and long
"mustache".
-Juli