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. 2018 Mar 14;4(3):eaar3748.
doi: 10.1126/sciadv.aar3748. eCollection 2018 Mar.

Earthquakes drive large-scale submarine canyon development and sediment supply to deep-ocean basins

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Earthquakes drive large-scale submarine canyon development and sediment supply to deep-ocean basins

Joshu J Mountjoy et al. Sci Adv. .

Abstract

Although the global flux of sediment and carbon from land to the coastal ocean is well known, the volume of material that reaches the deep ocean-the ultimate sink-and the mechanisms by which it is transferred are poorly documented. Using a globally unique data set of repeat seafloor measurements and samples, we show that the moment magnitude (Mw) 7.8 November 2016 Kaikōura earthquake (New Zealand) triggered widespread landslides in a submarine canyon, causing a powerful "canyon flushing" event and turbidity current that traveled >680 km along one of the world's longest deep-sea channels. These observations provide the first quantification of seafloor landscape change and large-scale sediment transport associated with an earthquake-triggered full canyon flushing event. The calculated interevent time of ~140 years indicates a canyon incision rate of 40 mm year-1, substantially higher than that of most terrestrial rivers, while synchronously transferring large volumes of sediment [850 metric megatons (Mt)] and organic carbon (7 Mt) to the deep ocean. These observations demonstrate that earthquake-triggered canyon flushing is a primary driver of submarine canyon development and material transfer from active continental margins to the deep ocean.

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Figures

Fig. 1
Fig. 1. Central New Zealand land and seafloor showing the 1500-km-long Hikurangi Channel that traverses the incoming plate of the subduction margin and feeds the Hikurangi fan drift in the Pacific Ocean east of the North Island.
The channel is fed by >10 major submarine canyons along the 370-km length of the shelf break, including the Kaikōura Canyon in the south. The Kaikōura earthquake surface fault ruptures are shown in red (14). Blue lines show the major active tectonic structures. Yellow circles show locations where the coseismic turbidite has been sampled, scaled to deposit thickness (T). The bottom right inset shows the detailed morphology of the entrenched Hikurangi Channel with coseismic turbidite sample sites indicated by stars.
Fig. 2
Fig. 2. Sedimentary evidence for a large-scale sediment gravity flow triggered by the Kaikōura earthquake that originated in the Kaikōura Canyon and traversed the deep-sea Hikurangi Channel.
(A) Photographic image, x-ray computed tomography (CT), sedimentology (c, clay; z, silt; fs, fine sand; ms, medium sand), and excess 234Th chronology (234Thex) for representative cores from the Hikurangi Channel floor and levee demonstrating very recent turbidite emplacement. The dimensions of the flow are demonstrated by bathymetric (Bathy) profiles showing the height of the Hikurangi Channel levee and core locations that contain the recent flow deposit, which indicate a minimum local flow thickness of 220 m, ~300 km along the channel (B), and 180 m, ~680 km along the channel (C). See Fig. 1 for transect locations.
Fig. 3
Fig. 3. Coseismic change in the Kaikōura Canyon.
(A) Digital elevation model (DEM) of the Kaikōura Canyon bathymetry (in grayscale) with overlaid magnitude of erosion and deposition within the canyon, measured by differencing the pre- and post-earthquake bathymetry data sets. Inset panels (top right) show (B) pre-earthquake and (C) post-earthquake bathymetry where coseismic landslides have occurred at the canyon rim (location on the canyon rim indicated by a rectangle). (D) Coarse sediment wave displacement vectors in the lower canyon. Black arrows denote bedform migration vectors. Red arrows show mean vectors for different sections of the sediment wave field (Supplementary Materials). (E) Zoom and long profile of the post-earthquake bathymetry of the sediment waves to illustrate the scale and profile form of these features.
Fig. 4
Fig. 4. Pre- and post-earthquake seafloor photographs from towed camera transects in the head of the Kaikōura Canyon (locations in the Supplementary Materials).
(A) Image of the pre-earthquake seafloor in November 2006 showing high densities of benthic foraminifera and sediment bioturbation by infaunal organisms. (B) Image from the same location as (A), captured in January 2017, 10 weeks post-earthquake, showing uniform fine sediments with no signs of benthic invertebrate life. (C) January 2017, rock fall and fine sediments. (D) January 2017, bacterial mat (gray patch on the top right) on sediment surface. Scale bars, 20 cm.

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