Monterey Bay Aquarium Research Institute

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

April 7, 2001: Leg 2; Day 7


Mega-bioturbation (whale divot?)

Juli Morgan writes: Once again, our night transit took us to the southeast side of the Big Island of Hawaii, in anticipation of fair conditions for diving onto Loihi Seamount, the youngest volcano in the Hawaiian chain. Continuing rough seas and high winds prevented us from diving onto Loihi, but we dropped two gravity cores into the volcano's main pit, in hopes of recovering the thick mud observed there previously. One core came up empty, but the other recovered a nice selection of basalt fragments from the top of Loihi - unusual for a device designed for sampling soft sediments! 

But rather than waste time wishing for good weather on the windward side of the island, we steamed back to the leeward side, and carried out a very successful and surprising dive onto the steep face of a block off the southwest flank of Mauna Loa. This block lies seaward and downslope of yesterday's dive, but also along the southern lateral margin of the Alika debris slide. In contrast to yesterday's dive, which sampled exhumed pillow basalts defining the primary edifice of Mauna Loa, today we discovered massive deposits of volcaniclastic strata: angular breccias and cohesive talus aprons that formed low slopes, and indurated volcanic sandstones that defined steep, high cliffs incised by dramatic erosional channels. The rocks were consistently fractured and jointed, and occasionally highly sheared, suggesting a past that included major faulting and displacement relative to the volcano flank on which they originated. The discovery and recovery of deformed volcaniclastic sediments on the seaward block confirms the interpretation of a major submarine landslide in this region, and opens the possibility of determining age and depositional sequences in the submarine regions of the active volcano.



Spire of sheared, jointed, volcaniclastic sediments.

Outcrop of chaotic volcaniclastic breccia.

Balloon sponge.

 

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