Modeling the topography of shallow braided rivers using Structure-from-Motion photogrammetry

Evaluating conflicting theories about the influence of mountains on carbon dioxide cycling and climate requires understanding weathering fluxes from tectonically uplifting landscapes. The lack of soil production and weathering rate measurements in Earth’s most rapidly uplifting mountains has made it difficult to determine whether weathering rates increase or decline in response to rapid erosion. Beryllium-10 concentrations in soils from the western Southern Alps, New Zealand, demonstrate that soil is produced from bedrock more rapidly than previously recognized, at rates up to 2.5 millimeters per year. Weathering intensity data further indicate that soil chemical denudation rates increase proportionally with erosion rates. These high weathering rates support the view that mountains play a key role in global-scale chemical weathering and thus have potentially important implications for the global carbon cycle.

/pdf/rapid-soil-production-and-weathering-in-the-southern-alps-nssfhcfzgh.pdf

Rapid Soil Production and Weathering in the Southern Alps, New Zealand

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.

https://advances.sciencemag.org/content/advances/4/3/eaar3748.full.pdf

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

Tracking the relationship between mountain uplift, silicate weathering, and long-term CO2 consumption with Ca isotopes: Southern Alps, New Zealand

The majority of the world's mangrove forests occur on mostly mineral sediments of fluvial origin. Two perspectives exist on the biogeomorphic development of these forests, i.e. that mangroves are opportunistic, with forest development primarily driven by physical processes, or alternatively that biophysical feedbacks strongly influence sedimentation and resulting geomorphology. On the Firth of Thames coast, New Zealand, we evaluate these two possible scenarios for sediment accumulation and forest development using high-resolution sedimentary records and a detailed chronology of mangrove-forest (Avicennia marina) development since the 1950s. Cores were collected along a shore-normal transect of known elevation relative to mean sea level (MSL). Activities for lead-210 (Pb-210), caesium-137 (Cs-137) and beryllium-7 (Be-7), and sediment properties were analysed, with Pb-210 sediment accumulation rates (SARs), compensated for deep subsidence (similar to 8 mm yr(-1)) used as a proxy for elevation gain. At least four phases of forest development since the 1950s are recognized. An old-growth forest developed by the late-1970s with more recent seaward forest expansion thereafter. Excess 210Pb profiles from the old-growth forest exhibit relatively low SARs near the top (7-12 mm yr(-1)) and bottom (10-22 mm yr(-1)) of cores, separated by an interval of higher SARs (33-100 mm yr(-1)). A general trend of increasing SAR over time characterizes the recent forest. Biogeomorphic evolution of the system is more complex than simple mudflat accretion/progradation and mangrove-forest expansion. Surface-elevation gain in the old-growth forest displays an asymptotic trajectory, with a secondary depocentre developing on the seaward mudflat from the mid-1970s. Two-to ten-fold increases in 210Pb SARs are unambiguously large and occurred years to decades before seedling recruitment, demonstrating that mangroves do not measurably enhance sedimentation over annual to decadal timescales. This suggests that mangrove-forest development is largely dependent on physical processes, with forests occupying mudflats once they reach a suitable elevation in the intertidal. Copyright (C) 2015 John Wiley & Sons, Ltd.

Mangrove‐forest evolution in a sediment‐rich estuarine system: opportunists or agents of geomorphic change?

River suspended sediment yield estimates from 233 New Zealand catchments are presented and used to calibrate an empirical, raster-type GIS model for predicting suspended sediment yield from any river in New Zealand. The calibration dataset is mostly based on suspended sediment gaugings and flow records, but includes data from lake and fiord bed sedimentation studies. The model relates sediment yield to the spatial integration of the product of a 'driving' factor and a 'supply' factor. The driving factor is P 1.7, where P is the local mean annual precipitation extracted from a precipitation grid. The supply factor depends on an erosion terrain classification that spreads erosion potential by slope and lithology, and to some extent by erosion process. With 74 unique terrains defined for New Zealand, coefficients for each terrain were determined by a range of approaches based on the availability of calibration data. Comparison of measured yields with those predicted by a preliminary calibration procedure highlighted several regions with systematic over-or under-prediction. These regions have differences in land cover, glacial history, tectonic regime, and/or climate that are not incorporated into the erosion terrain classification or the driving factor based on mean annual rainfall. Separate coefficients were determined for the dominant erosion terrains in each special region. With these adjustments, the model explained 97% and 96% of the variance in the measured South and North Island (log-transformed) yields, respectively, while the standard errors of the predictions equated to factors of 1.55 and 1.8 for the South and North Islands catchments, respectively. The factorial error in predicted yield decreased as catchment area increased. When totalled over all measured catchments, the predicted yield differed from the measured yield by only 2.3% in the South Island and 6.5% in the North Island. Summing measured yields and model-predicted yields from ungauged catchments, the South Island yield is 91 Mt/y and the North Island yield is 118 Mt/y. Natural lakes intercept 14% of the potential sediment yield of the South Island but only 1% of that of the North Island. Hydro-lakes intercept 3% of the South Island yield and 0.3% of the North Island yield. Overall, floodplains and estuaries intercept only a small percentage of the total sediment delivery to the coast (although this may not be the case for particular floodplains or estuaries). The 209 Mt/y total suspended sediment yield from New Zealand amounts to 1.7% of the global sediment delivery to the oceans, making New Zealand a significant contributor on a unit area basis by virtue of its steep terrain, high rainfall, and tectonic activity. The sediment yield model is available in an easily used form on the Internet (http://wrenz.niwa.co.nz/webmodel), but in its present form it is not suited to assessing the effects of changes in land cover or land use on sediment delivery because this was not explicitly included as a controlling factor.

Suspended Sediment Yields from New Zealand Rivers

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Suspended Sediment Yields from New Zealand Rivers