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Site of recent
multichannel seismic survey, over the submarine south flank
of Kilauea Volcano, Hawaii. Major geographic features are
labelled, and the tracks of the seismic lines marked. The
morphology of the south flank has many features suggestive
of a landslide: the Hilina fault zone, just seaward of
Kilauea's summit, is thought to define the headwall of a
slump. A midslope bench at about 2500 mbsl may represent
the uplifted toe of the slump. The southwestern margin is
defined by a lineament upon which Papa'u seamount sits. New
interpretations of the flank's substructure based on the
seismic data, however, suggest that some of these features
may result from lateral displacement of the entire flank,
rather than surficial collapse.
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Abstract
A multichannel seismic survey onboard the R/V Maurice
Ewing in 1998 provided a first look at the subsurface
structure of the mobile south flank of Kilauea volcano. An
example of an oceanic volcano built upon older, sedimented
oceanic crust, Kilauea volcano responds to magmatic
intrusion and upward growth through a combination of lateral
volcanic spreading and landsliding; reflection data over the
submarine flank reveal structures indicative of both
processes. A prominent basal reflection occurs on all
lines, ranging in depth from 6 km at the seaward edge of the
flank, to ~8 km near the shoreline; its depth and regional
extent identify this reflection as the top of the Cretaceous
oceanic crust upon which the volcano was built. Landward
dipping reflections rise from the oceanic crust reflection,
folding overlying strata and building a 4 km high bench
behind which ponded sediments are back-rotated. Composed of
volcaniclastic sands and breccias, possibly landslide
debris, the bench reflects overthrusting and accretion of
strata due to seaward sliding of the mobile flank; the slip
surface is interpreted at or near the top of the oceanic
crust. The southwest boundary of the submarine flank shows
a step down to the southwest attributed to strike slip
displacement of the flank. Papa'u seamount , an elongate
ridge built upon this boundary, is constructed of a 1 km
thick package of folded slope sediments. Although Papa'u
may result from deeply rooted overthrusting as observed
lower on the flank, its oblique vergence and proximity to
the on-land extensional Hilina fault system suggest
alternatively that it may be the submarine manifestation of
an active slump. Well-bedded sediments that drape the
submarine flanks are also locally folded and truncated;
small translational slide blocks and accumulations of
chaotic debris point to shallow slope failures. The
subsurface geology of Kilauea's submarine flank suggests
primary deformation by seaward sliding and distal
overthrusting due to volcanic spreading, subsequently
overprinted by slope failure and landsliding. These
processes are driven by volcanic processes, providing an
important record of the volcano's activity and growth.
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