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Deep Ocean Responses to Geological and Climatic Catastrophes along the New Zealand Plate Boundary.
by
Lionel Carter
National Institute of Water and Atmosphere (NIWA)
Coauthors: Keith Lewis (NIWA), Alan Orpin (NIWA)
The position of New Zealand across an active collisional plate boundary, together with a vigorous climate, means the adjacent deep ocean is periodically subjected to catastrophes associated with floods, major volcanic eruptions, large earthquakes and mass failures of the seabed. High resolution multibeam mapping and palaeoenvironmental analyses of deep ocean cores collected near the plate boundary off the North Island, reveal a range of responses to the aforementioned events.
Climate has a strong El Niņo- Southern Oscillation component. In La Niņa years, subtropical cyclones, such as the 1988 Bola event, was accompanied by exceptional floods which discharged large volumes of sediment (40 million tonnes for one river) to the continental shelf. Hypopycnal flows produced fluid mud layers up to 2 m thick across the seabed. Benthic communities were smothered but rapidly recolonised following dispersal of the fluid mud layer.
The Holocene witnessed 5 major eruptions from the North Island's Taupo Volcanic Zone - the world's most prolific rhyolitic centre. Airfall and ignimbrites, which in the case of the 1.718 ka Taupo event had a combined volume of >100 cubic km, destroyed vegetation. Erosion of the denuded landscape, with its mantle of unconsolidated volcanic debris, increased the sediment flux to the ocean. Such pulses lasted for a century of more before forests re-established. In addition, direct deposition of airfall on the ocean floor locally smothered benthic communities when the resultant tephra deposit exceeded about 1 cm thickness.
Large earthquakes are a feature of the region. Onshore, seismic destabilisation of hill slopes was followed by pulses of sediment to the continental shelf. There, efficient trapping by the shelf morphology and coast-parallel transport regime, buffered the adjacent deep ocean from the influx. However, seismic ground shaking of the continental slope has generated sheet slides, slumps, debris flows and avalanches. Some of these mass failure deposits, such as the 720 cubic km Kidnappers Slide, developed in several stages throughout the Holocene.
Date received: March 21, 2002
Copyright © 2002 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caiq-86.