Abstract
AbstractThis study describes the geomorphometries of archipelagic aprons on the southern flanks of the French Frigate Shoals and Necker Island edifices on the central Northwest Hawaiian Ridge that are hotspot volcanoes that have been dormant for 10–11 m.y. The archipelagic aprons are related to erosional headwall scarps and gullies on landslide surfaces but also include downslope gravitational features that include slides, debris avalanches, bedform fields, and outrunners. Some outrunners are located 85 km out onto the deep seafloor in water depths of 4900 m. The bedforms are interpreted to be the result of slow downslope sediment creep rather than products of turbidity currents. The archipelagic aprons appear to differ in origin from those off the Hawaiian Islands. The landslides off the Hawaiian Islands occurred because of oversteepening and loading during the constructive phase of the islands whereas the landslides off the French Frigate Shoals and Necker Island edifices may have resulted from vertical tectonics due to the uplift and relaxation of a peripheral bulge or isolated earthquakes long after the edifices passed beyond the hotspot. The lack of pelagic drape in water depths above the 4600 m depth of the local carbonate compensation depth suggests that the archipelagic apron off the French Frigate Shoals edifice is much younger, perhaps Quaternary in age, than that off the Necker Island edifice, which has a 50 m pelagic drape. The pelagic drape off the Necker Island edifice suggests that the landslides may be as old as 9 Ma. The lack of pelagic drape off the French Frigate Shoals edifice suggests that the most recent landslides are more recent, perhaps even Quaternary in age. The presence of a chute-like feature on the mid-flank of the French Frigate Shoals edifice appears to be the result of rejuvenated volcanism that occurred long after the initial volcanism ceased to build the edifice.
Highlights
Archipelagic aprons are submarine landslide complexes composed of erosion and depositional gravity flows that involve both sediment and blocks of the insular flanks
This study describes the surface geomorphometries of archipelagic aprons off the southern flanks of the French Frigate Shoals and Necker Island edifices in the central Northwest Hawaiian Ridge
The archipelagic aprons are composed of a sequence of landslide features that include (1) headwall scarps on the upper flanks of the two edifices, (2) downslope-directed gullies on the upper slide surfaces, (3) intact slides on the upper and mid flanks, (4) debris avalanches that spread out downslope from the mid and lower flanks, (5) fields of sediment creep that blanket large areas on the lower flanks out onto the deep seafloor, and (6) outrunner blocks that are scattered on the lower flanks and deep seafloor that have traveled as much as 85 km from the base of the edifice
Summary
Archipelagic aprons are submarine landslide complexes composed of erosion and depositional gravity flows that involve both sediment and blocks of the insular flanks. Landslides, turbidity flows, etc., that are composed of volcaniclastic debris that creates gravity-driven downslope processes that themselves further erode the flanks of islands, seamounts, and guyots and deposit material at the base of the edifices. Key discoveries since Menard’s studies conclude that (1) seamounts repeatedly build and collapse so that a greater volume of masswasted volcaniclastic material can accumulate as compared to the volume of a single complete seamount (e.g., Hunt and Jarvis, 2020); (2) the process of slope failure begins early in the history of a seamount, such that landslide debris is a component of the internal structure of the seamount itself (e.g., Keating and McGuire, 2004); and (3) archipelagic aprons form around guyots and seamounts that have never been near or above sea level (e.g., Schmincke et al, 1995; Fig. 2). The massive submarine landslides off the Hawaiian Islands described by Lipman et al (1988) and Moore et al (1989) are an extreme class of archipelagic aprons (Fig. 5)
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