HR: 0800h
AN: H31A-1282    [Abstracts]
TI: Late Quaternary Large-Scale Rock-Mass Defect Controlled Landslides of Eastern North Island, New Zealand: Tectonic and Climatic Forcing in Landscape Evolution
AU: * Pettinga, J R
EM: jarg.pettinga@canterbury.ac.nz
AF: Geological Sciences, University of Canterbury, , Private Bag 4800, , Christchurch, 8020 New Zealand
AU: McKean, J A
EM: jmckean@fs.fed.us
AF: USDA Forest Service, Rocky Mountain Research Station, 316 E. Myrtle Street, Boise, ID 83702 United States
AU: Mountjoy, J
H31A-1282 AF: Geological Sciences, University of Canterbury, , Private Bag 4800, , Christchurch, 8020 New Zealand
AU: Pere, V H
H31A-1282 AF: Geological Sciences, University of Canterbury, , Private Bag 4800, , Christchurch, 8020 New Zealand
AU: Leith, K
H31A-1282 AF: Geological Sciences, University of Canterbury, , Private Bag 4800, , Christchurch, 8020 New Zealand
AU: Mackey, B
H31A-1282 AF: Geological Sciences, University of Canterbury, , Private Bag 4800, , Christchurch, 8020 New Zealand
AB: Rock mass defect controlled landslides are widespread in the Tertiary bedded marine soft rock terrain of eastern North Island. The location and frequency of these deep-seated bedrock landslides is somewhat predictable and the slides are a dominant process affecting both sediment fluxes and landscape evolution. Most slides appear to be base level controlled and occur after stream incision has exposed a critical stratigraphic horizon, defined by thin (typically <20mm), comparatively weak and laterally continuous bedding parallel layers. These horizons are of sedimentary origin (e.g. bedding partings; thin sand, clay and volcanic ash horizons) and may have experienced some prior tectonically induced shear displacement (e.g. flexural slip and/or fault shear). The residual strength of these sedimentary horizons (C_r' = 2.6 _ 20 kPa, and Φr = 2° _ ~20°) is very low relative to the peak strength of the dominant lithology (C_r' = <300 kPa, and Φr = 30° _ 37°). New failures are triggered episodically as deeper critical stratigraphic horizons daylight following stream incision. Failure on multiple near horizontal critical stratigraphic horizons leads to the development of a `stepped' landscape morphology with extensive block slides, while wedge failures dominate catchments with moderately dipping successions. Orthogonal rock defects also partly control the lateral slide boundaries. The slides are triggered by both short- and long-term tectonic (earthquakes; regional uplift) and climatic (seasonal and glacio-eustatic cycles) forcing. Large bedrock landslide dams are recognized in a number of catchments (e.g. Ngatapa, Waipaoa, Tutira, Waikaremoana, Ponui) and these transient features block drainages and dramatically alter catchment sediment fluxes for periods ranging up to 10⁴ years. Reservoir deposits allow quantification of the degree and timing of perturbations to sediment flux, and provide constraints on variations in catchment sediment yield attributable to long-term glacio-eustatic climatic forcing cycles. The influence of these large slope failures is likely to affect the geomorphic development of catchments over a time scale of 10⁴ to 10⁵ years. We have quantified key material strength and landslide geometry parameters that allow numerical landscape evolution models to include large bedrock failures. Such models are needed to investigate the range of conditions leading to sliding (e.g. uplift rates, incision rates, earthquake recurrence and shaking intensity) and the geomorphic consequences of the failures.
DE: 1804 Catchment
DE: 1815 Erosion
DE: 1826 Geomorphology: hillslope (1625)
DE: 8175 Tectonics and landscape evolution
SC: Hydrology [H]
MN: Fall Meeting 2005