HR: 1340h
AN: OS33B-1474    [Abstracts]
TI: Erosion of Uplifted Ridges at the Top of Gas Hydrate Stability and its Implications: Evidence from the Hikurangi Margin, New Zealand
AU: * Pecher, I A
EM: i.pecher@gns.cri.nz
AF: Insitute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6009 New Zealand
AU: Ellis, S
EM: s.ellis@gns.cri.nz
AF: Insitute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6009 New Zealand
AU: Faure, K
EM: k.faure@gns.cri.nz
AF: Insitute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6009 New Zealand
AU: Massoth, G
EM: g.massoth@gns.cri.nz
AF: Insitute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6009 New Zealand
AU: Graham, I
EM: i.graham@gns.cri.nz
AF: Insitute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6009 New Zealand
AU: Henrys, S A
EM: s.henrys@gns.cri.nz
AF: Insitute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6009 New Zealand
AU: Chiswell, S M
EM: s.chiswell@niwa.cri.nz
AF: National Institute of Water and Atmospheric Research, Private Bag 14907, Wellington, 6003 New Zealand
AU: Kukowski, N
EM: nina@gfz-potsdam.de
AF: Geoforschungszentrum Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AB: Rock Garden, an uplifted ridge on the Hikurangi Margin offshore of New Zealand, appears to be eroded at ~ 600 m water depth. Pinchouts of bottom simulating reflections (BSRs) at the edges of its plateau-like crest and theoretical phase boundary considerations in combination with water temperature data suggest that most likely, erosion is linked to the top of gas hydrate stability in the ocean. We propose a combination of two mechanisms that may cause seafloor erosion during ridge uplift. An upward migrating base of gas hydrate stability with respect to the seafloor caused by depressurization during uplift may lead to overpressure and sliding. After sliding, water depth and hence, hydrate stability, increases again and the process may repeat itself during continued uplift. We present evidence from bathymetric and seismic data that support the presence of small slides on the edges of the plateau. However, for this mechanism to be efficient, the ridge crest must remain within the gas hydrate stability field, which seems to contradict the presence of BSR pinchouts. On the ridge crest, we predict gas hydrates close to the seafloor to repeatedly form and dissociate because of water temperature fluctuations and suggest that resulting pore volume contraction and expansion may cause a frost-heave-like weakening of the seafloor. We discuss the viability of both mechanisms. We also discuss the possibility that ridges like Rock Garden may focus methane transport from deeper sources towards the ridge crests where it may be released into the ocean, an effect that may increase the amount of methane released into intermediate-water depths.
DE: 0935 Seismic methods (3025, 7294)
DE: 3004 Gas and hydrate systems
DE: 3025 Marine seismics (0935, 7294)
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 3070 Submarine landslides
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005