scholarly journals Histories and Mechanisms of Change in the Development of Shore Platforms at Kaikoura and Rodney New Zealand: Application of Cosmogenic Nuclides and Numerical Modelling on Exposed Coastal Surfaces

2021 ◽  
Author(s):  
◽  
Aidan Duart McLean
Keyword(s):  
New Zealand ◽  
Numerical Modelling ◽  
Sea Level ◽  
Late Holocene ◽  
Cosmogenic Nuclides ◽  
Erosion Rates ◽  
Cliff Erosion ◽  
Exposure Ages ◽  
Shore Platforms

<p>Global sea level rise is contributing to the acceleration of cliff erosion rates in New Zealand, where it surpasses rates of uplift. A significant challenge facing scientists and managers is that we have no method for reliably extracting past rates of coastal erosion along harder rock cliffs over the time-scales that significant sea level change occurs (100s-1000s of years). This gap in knowledge is limiting efforts to model and understand the relationship between sea level rise and cliff erosion rates and what form of that relationship takes. Cosmogenic Beryllium-10 analysis has been applied on two low angle shore platforms in New Zealand to produce chronologies of sea cliff retreat during the late-Holocene. Surface exposure ages were attained on a tectonically active platform at Kaikoura, Canterbury and a tectonically quiescent platform at Cape Rodney, Auckland. This is the first application of cosmogenic nuclides to a shore platform study in New Zealand and adds two new data-sets to the very small group of global shore platform chronologies. Exposure ages show New Zealand platforms have developed in the late-Holocene. Long-term platform surface erosion rates at Kaikoura (0.4mm a-1), potentially due to uplift driven positive feedback such as altered sea level position, driving up weathering rates on the tidally inundated platform. Nuclide concentrations at Okakari Point, Rodney, reveal a significant role of recent sea level fall after ~4000yrs BP, driving surface denudation (0.1mm a-1). The long-term cliff back-wearing rate at Okakari point was found to be 24.66mm a-1. Patterns in cosmogenic nuclide concentrations in New Zealand’s shallow platforms differ from global examples recorded on steeper platforms. Exploratory numerical modelling was applied with the coupled Rocky Profile CRN model (RPM_CRN) to identify process relationships between key drivers within platform coastal systems and scenarios of sea level change and active tectonics. This combined geochemical and numerical modelling study has shown that shore platforms in New Zealand have complex histories, with different potential driving forces at Kaikoura and Okakari. This highlights the local variability in platform development and cliff retreat, suggesting that estimates of future shoreline erosion will need to take local contingencies into account.</p>

scholarly journals Histories and Mechanisms of Change in the Development of Shore Platforms at Kaikoura and Rodney New Zealand: Application of Cosmogenic Nuclides and Numerical Modelling on Exposed Coastal Surfaces

2021 ◽  
Author(s):  
◽  
Aidan Duart McLean
Keyword(s):  
New Zealand ◽  
Numerical Modelling ◽  
Sea Level ◽  
Late Holocene ◽  
Cosmogenic Nuclides ◽  
Erosion Rates ◽  
Cliff Erosion ◽  
Exposure Ages ◽  
Shore Platforms

<p>Global sea level rise is contributing to the acceleration of cliff erosion rates in New Zealand, where it surpasses rates of uplift. A significant challenge facing scientists and managers is that we have no method for reliably extracting past rates of coastal erosion along harder rock cliffs over the time-scales that significant sea level change occurs (100s-1000s of years). This gap in knowledge is limiting efforts to model and understand the relationship between sea level rise and cliff erosion rates and what form of that relationship takes. Cosmogenic Beryllium-10 analysis has been applied on two low angle shore platforms in New Zealand to produce chronologies of sea cliff retreat during the late-Holocene. Surface exposure ages were attained on a tectonically active platform at Kaikoura, Canterbury and a tectonically quiescent platform at Cape Rodney, Auckland. This is the first application of cosmogenic nuclides to a shore platform study in New Zealand and adds two new data-sets to the very small group of global shore platform chronologies. Exposure ages show New Zealand platforms have developed in the late-Holocene. Long-term platform surface erosion rates at Kaikoura (0.4mm a-1), potentially due to uplift driven positive feedback such as altered sea level position, driving up weathering rates on the tidally inundated platform. Nuclide concentrations at Okakari Point, Rodney, reveal a significant role of recent sea level fall after ~4000yrs BP, driving surface denudation (0.1mm a-1). The long-term cliff back-wearing rate at Okakari point was found to be 24.66mm a-1. Patterns in cosmogenic nuclide concentrations in New Zealand’s shallow platforms differ from global examples recorded on steeper platforms. Exploratory numerical modelling was applied with the coupled Rocky Profile CRN model (RPM_CRN) to identify process relationships between key drivers within platform coastal systems and scenarios of sea level change and active tectonics. This combined geochemical and numerical modelling study has shown that shore platforms in New Zealand have complex histories, with different potential driving forces at Kaikoura and Okakari. This highlights the local variability in platform development and cliff retreat, suggesting that estimates of future shoreline erosion will need to take local contingencies into account.</p>

Analysis of relationships between micro-topography and short- and long-term erosion rates on shore platforms at Kaikoura Peninsula, South Island, New Zealand

Geomorphology ◽  
2010 ◽  
Vol 121 (3-4) ◽  
pp. 266-273 ◽  
Author(s):  
R.J. Inkpen ◽  
W.J. Stephenson ◽  
R.M. Kirk ◽  
M.A. Hemmingsen ◽  
S.A. Hemmingsen
Keyword(s):  
New Zealand ◽  
Erosion Rates ◽  
Short And Long Term ◽  
Micro Topography ◽  
Shore Platforms

Evolution of a low-relief landscape in the Eastern Alps constrained by low-temperature thermochronology and cosmogenic nuclides

2020 ◽  
Author(s):  
Andreas Wölfler ◽  
Sebastian Reimers ◽  
Andrea Hampel ◽  
Christoph Glotzbach ◽  
István Dunkl
Keyword(s):  
Low Temperature ◽  
Fission Track ◽  
Eastern Alps ◽  
Cosmogenic Nuclides ◽  
Near Surface ◽  
Erosion Rates ◽  
Exposure Dating ◽  
Zircon Fission Track ◽  
Exposure Ages

&lt;p&gt;The relief history of mountain belts is strongly influenced by the interplay of tectonics and surface processes, which both shape Earth&amp;#180;s landscapes. In this context, the quantification of the rates of long-term and short-term processes is key for understanding landscape evolution and requires the application of methods that integrate over different timescales. In this study, we apply low-temperature thermochronology and cosmogenic nuclides to quantify the geological and geomorphic evolution of an elevated low-relief landscape in the Eastern Alps, the so-called Nock Mountains, which are situated to the east of the Tauern Window. The low-temperature thermochronological data yield zircon fission track and zircon (U-Th)/He cooling ages of 93.4&amp;#177;12.9 and 77.8&amp;#177;7.8 Ma, respectively, which we interpret to reflect late Cretaceous cooling after Eo-Alpine metamorphism. Apatite fission track and (U-Th)/He ages are significant younger and range from 36.8 to 31.3 Ma. Time-temperature history modelling of the cooling ages suggests enhanced cooling in the Eocene followed by thermal stagnation. Thus, the rocks of the study area have been in near surface position (2-3 km) since the Late Eocene. Enhanced cooling in the Eocene is probably related to an increasing relief due to shortening, folding and thrusting in the Eastern Alps triggered by the onset of collision between the European margin and the Adriatic microplate. Under the assumption that rock exhumation occurred solely by erosion, the long-term average erosion rate derived from the thermochronological data is ~50-90 mm/kyr. Catchment-wide erosion rates derived from cosmogenic &lt;sup&gt;10&lt;/sup&gt;Be in river sediments&amp;#160; range from 83&amp;#177;7 to 205&amp;#177;18 mm/kyr and hence are lower than in other parts of the Alps. As the &lt;sup&gt;10&lt;/sup&gt;Be-derived erosion rates and the long-term rates derived from thermochronology agree despite the different timescales over which the two methods integrate, our new data suggest that erosion rates did not change significantly over the last ~40 Ma. This is remarkable because within this time span numerous tectonic processes and glacial-interglacial cycles affected the study area. To investigate the deglaciation history after the Last Glacial Maximum in the Nock Mountains, we sampled glacially polished quartz veins for &lt;sup&gt;10&lt;/sup&gt;Be exposure dating. The first four exposure ages obtained so far cluster between 14.5&amp;#177;1.4 and 16.8&amp;#177;1.6 ka. We interpret these ages as the record the retreat of the ice cover in the study area shortly after the Oldest Dryas stadial.&lt;/p&gt;

scholarly journals Controls on the distribution of cosmogenic <sup>10</sup>Be across shore platforms

2016 ◽  
Author(s):  
Martin D. Hurst ◽  
Dylan H. Rood ◽  
Michael A. Ellis
Keyword(s):  
Coastal Change ◽  
Cosmogenic Radionuclides ◽  
Heterogeneous Distribution ◽  
Erosion Rates ◽  
Erosion Processes ◽  
Rocky Coast ◽  
Exposure Ages ◽  
Shore Platforms ◽  
Cliff Retreat

Abstract. Quantifying rates of erosion on cliffed coasts across a range of timescales is vital for understanding the drivers and processes of coastal change and for assessing risks posed by future cliff retreat. Historical records cover at best the last 150 years; Cosmogenic radionuclides, such as 10Be could allow us to look further into past to assess coastal change at millenial timescales. CRNs accumulate in-situ near the Earth surface and have been used extensively to quantify erosion rates, burial dates and surface exposure ages in terrestrial landscapes over the last three decades. More recently, applications in rocky coast settings have quantified the timing of mass wasting events, determined long-term-averaged rates of cliff retreat and revealed the exposure history of shore platforms. In this contribution, we developed and explored a numerical model for the accumulation of 10Be on eroding shore platforms. In a series of numerical experiments, we investigated the influence of topographic and water shielding, dynamic platform erosion processes, the presence and variation in beach cover, and heterogeneous distribution of erosion on the distribution of 10Be across shore platforms. Results demonstrate that, taking into account relative sea level change and tides, the concentration of 10Be is sensitive to rates of cliff retreat. Factors such as topographic shielding and beach cover, act to reduce 10Be concentrations on the platform, and may result in overestimation of cliff retreat rates if not accounted for. The shape of the distribution of 10Be across a shore platform can potentially reveal whether cliff retreat rates are declining or accelerating through time. Measurement of 10Be in shore platforms has great potential to allow us to quantify long-term rates of cliff retreat and platform erosion.

scholarly journals Controls on the distribution of cosmogenic <sup>10</sup>Be across shore platforms

2017 ◽  
Vol 5 (1) ◽  
pp. 67-84 ◽  
Author(s):  
Martin D. Hurst ◽  
Dylan H. Rood ◽  
Michael A. Ellis
Keyword(s):  
Coastal Change ◽  
Heterogeneous Distribution ◽  
Cosmogenic Isotopes ◽  
Erosion Rates ◽  
Erosion Processes ◽  
Rocky Coast ◽  
Exposure Ages ◽  
Shore Platforms ◽  
Cliff Retreat

Abstract. Quantifying rates of erosion on cliffed coasts across a range of timescales is vital for understanding the drivers and processes of coastal change and for assessing risks posed by future cliff retreat. Historical records cover at best the last 150 years; cosmogenic isotopes, such as 10Be could allow us to look further into the past to assess coastal change on millennial timescales. Cosmogenic isotopes accumulate in situ near the Earth surface and have been used extensively to quantify erosion rates, burial dates and surface exposure ages in terrestrial landscapes over the last 3 decades. More recently, applications in rocky coast settings have quantified the timing of mass wasting events, determined long-term averaged rates of cliff retreat and revealed the exposure history of shore platforms. In this contribution, we develop and explore a numerical model for the accumulation of 10Be on eroding shore platforms. In a series of numerical experiments, we investigated the influence of topographic and water shielding, dynamic platform erosion processes, the presence and variation in beach cover, and heterogeneous distribution of erosion on the distribution of 10Be across shore platforms. Results demonstrate that, taking into account relative sea level change and tides, the concentration of 10Be is sensitive to rates of cliff retreat. Factors such as topographic shielding and beach cover act to reduce 10Be concentrations on the platform and may result in overestimation of cliff retreat rates if not accounted for. The shape of the distribution of 10Be across a shore platform can potentially reveal whether cliff retreat rates are declining or accelerating through time. Measurement of 10Be in shore platforms has great potential to allow us to quantify long-term rates of cliff retreat and platform erosion.

Erosion rates of the New Zealand Southern Alps reflect long-term tectonics and transient climate

2021 ◽  
Author(s):  
Duna Roda-Boluda ◽  
Taylor Schildgen ◽  
Hella Wittmann-Oelze ◽  
Stefanie Tofelde ◽  
Aaron Bufe ◽  
...  
Keyword(s):  
New Zealand ◽  
Strike Slip ◽  
Southern Alps ◽  
Fault System ◽  
Tectonic Deformation ◽  
Seismic Cycle ◽  
Erosion Rates ◽  
Alpine Fault ◽  
Oblique Convergence

&lt;p&gt;The Southern Alps of New Zealand are the expression of the oblique convergence between the Pacific and Australian plates, which move at a relative velocity of nearly 40 mm/yr. This convergence is accommodated by the range-bounding Alpine Fault, with a strike-slip component of ~30-40 mm/yr, and a shortening component normal to the fault of ~8-10 mm/yr. While strike-slip rates seem to be fairly constant along the Alpine Fault, throw rates appear to vary considerably, and whether the locus of maximum exhumation is located near the fault, at the main drainage divide, or part-way between, is still debated. These uncertainties stem from very limited data characterizing vertical deformation rates along and across the Southern Alps. Thermochronology has constrained the Southern Alps exhumation history since the Miocene, but Quaternary exhumation is hard to resolve precisely due to the very high exhumation rates. Likewise, GPS surveys estimate a vertical uplift of ~5 mm/yr, but integrate only over ~10 yr timescales and are restricted to one transect across the range.&lt;/p&gt;&lt;p&gt;To obtain insights into the Quaternary distribution and rates of exhumation of the western Southern Alps, we use new &lt;sup&gt;10&lt;/sup&gt;Be catchment-averaged erosion rates from 20 catchments along the western side of the range. Catchment-averaged erosion rates span an order of magnitude, between ~0.8 and &gt;10 mm/yr, but we find that erosion rates of &gt;10 mm/yr, a value often quoted in the literature as representative for the entire range, are very localized. Moreover, erosion rates decrease sharply north of the intersection with the Marlborough Fault System, suggesting substantial slip partitioning. These &lt;sup&gt;10&lt;/sup&gt;Be catchment-averaged erosion rates integrate, on average, over the last ~300 yrs. Considering that the last earthquake on the Alpine Fault was in 1717, these rates are representative of inter-seismic erosion. Lake sedimentation rates and coseismic landslide modelling suggest that long-term (~10&lt;sup&gt;3&lt;/sup&gt; yrs) erosion rates over a full seismic cycle could be ~40% greater than our inter-seismic erosion rates. If we assume steady state topography, such a scaling of our &lt;sup&gt;10&lt;/sup&gt;Be erosion rate estimates can be used to estimate rock uplift rates in the Southern Alps. Finally, we find that erosion, and hence potentially exhumation, does not seem to be localized at a particular distance from the fault, as some tectonic and provenance studies have suggested. Instead, we find that superimposed on the primary tectonic control, there is an elevation/temperature control on erosion rates, which is probably transient and related to frost-cracking and glacial retreat.&lt;/p&gt;&lt;p&gt;Our results highlight the potential for &lt;sup&gt;10&lt;/sup&gt;Be catchment-averaged erosion rates to provide insights into the magnitude and distribution of tectonic deformation rates, and the limitations that arise from transient erosion controls related to the seismic cycle and climate-modulated surface processes.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

Surface erosion assessment in the South-Canterbury downlands, New Zealand using 137Cs distribution

Soil Research ◽  
1995 ◽  
Vol 33 (5) ◽  
pp. 787 ◽  
Author(s):  
LR Basher ◽  
KM Matthews ◽  
L Zhi
Keyword(s):  
New Zealand ◽  
Mean Value ◽  
Slope Position ◽  
Surface Erosion ◽  
The South ◽  
Erosion And Deposition ◽  
Erosion Rates ◽  
Land Use Types ◽  
Radionuclide Tracer

Redistribution of the radionuclide tracer 137Cs was used to examine the pattern of erosion and deposition at two sites with contrasting long-term land uses (pasture and cropping) in the South Canterbury downlands, New Zealand. There were clear differences between the two land use types in variation in 137Cs concentrations and areal activity, erosion rates and topsoil depth variability. Erosion and deposition have resulted in greater variability and lower mean levels of 137Cs areal activity under cropping (46.3 mBq cm-2) than pasture (55.0 mBq cm-2). At the cropping site, erosion and deposition roughly balanced with the mean value over all sampling sites, suggesting no net soil loss, but considerable redistribution of soil within paddocks. At the pasture site results suggested slight net deposition. There was evidence for both sheet/rill and wind erosion being important in soil redistribution. While there was no difference in mean topsoil depth between pasture and cropping, there were significant differences with slope position. At the pasture site, there was little variation of topsoil depth with slope position, except for swales which tended to be deeper, whereas at the cropping site there was considerable variation in topsoil depth with slope position. Topsoil depth was a poor indicator of erosion status.

scholarly journals Late Holocene sea-level changes and vertical land movements in New Zealand

2020 ◽  
pp. 1-16
Author(s):  
Daniel J. King ◽  
Rewi M. Newnham ◽  
W. Roland Gehrels ◽  
Kate J. Clark
Keyword(s):  
New Zealand ◽  
Sea Level ◽  
Late Holocene ◽  
Sea Level Changes ◽  
Holocene Sea Level

Spatially Averaged Long-Term Erosion Rates Measured from in Situ-Produced Cosmogenic Nuclides in Alluvial Sediment

1996 ◽  
Vol 104 (3) ◽  
pp. 249-257 ◽  
Author(s):  
Darryl E. Granger ◽  
James W. Kirchner ◽  
Robert Finkel
Keyword(s):  
Cosmogenic Nuclides ◽  
Erosion Rates ◽  
Alluvial Sediment
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