Line 2 - Depth Section and Interpretation

Line 2 crosses the broadest part of the midslope bench, as well as an elongate landslide block in front of the slope.

The upper flank is composed of submarine erupted basalts
covered by a 1 km thick blanket of hyaloclastite slope sediments.

The midslope bench is constructed of an imbricate stack of thrust sheets
derived from stratified sediments and debris accumulated in front of flank.

The bench traps hyaloclastic sediments in a midslope basin;
these are back-rotated and uplifted by continuing growth of the bench.

A strong reflection can be followed beneath the upper flank,
midslope bench, and sediments, blocks and debris in the Hawaiian Deep.
We interpret this as the top of the Cretaceous oceanic crust and pelagic sediment cover.
Strong reflections above this deep horizon define thrust faults and base of volcanic edifice.


These data provide evidence for the process of volcanic spreading. The volcanic edifice slides seaward along pelagic sediment layer on the pre-existing volcanic plate; thrust faults break the primary volcanic edifice, and deform overlying strata and sediment cover. Strata in the volcaniclastic apron are accreted to the toe of the sliding flank, leading to growth and uplift of the midslope bench. Shortening estimates range from 10 to 20 km, consistent with the interpreted width of an intrusive core of dikes beneath the summit and rift zone.