scholarly journals The influence of wave power on bedrock sea-cliff erosion in the Hawaiian Islands

Geology ◽  
2020 ◽  
Vol 48 (5) ◽  
pp. 499-503 ◽  
Author(s):  
Kimberly L. Huppert ◽  
J. Taylor Perron ◽  
Andrew D. Ashton
Keyword(s):  
Sea Level ◽  
Coastal Erosion ◽  
Wave Power ◽  
Relative Sea Level ◽  
Cliff Erosion ◽  
Field Evidence ◽  
Coastal Profile ◽  
Sea Cliff ◽  
Best Fit ◽  
Cliff Retreat

Abstract Waves erode sea cliffs by various mechanisms, but the influence of wave power on bedrock coastal erosion has not been well quantified, making it difficult to predict how rocky coasts evolve in different environments. Volcanic ocean islands offer a unique opportunity to examine the influence of waves on bedrock coastal erosion because many islands have relatively homogeneous bedrock, well-constrained initial topography, and considerable differences in wave power between shorelines that face different directions and wave regimes. We used lava-flow ages and the morphology of coastal profiles on Maui, Kaho‘olawe, and the Big Island of Hawai‘i (USA) to estimate sea-cliff retreat rates at 11 sites that experience nearly eightfold differences in incident wave power. Using a range of possible sea-level histories that incorporate different trends of subsidence due to volcanic loading, we modeled the evolution of each coastal profile since its formation (12 ka to 1.4 Ma) to find the regionally consistent relative sea-level history and the site-specific sea-cliff retreat rates that best reproduce observed coastal profiles. We found a best-fit relative sea-level history prescribed by an effective elastic lithosphere thickness of 30 km, consistent with estimates from observations of total deflection beneath the Hawaiian Ridge. This suggests that coastal profiles may retain a decipherable record of sea-level change. Comparing the best-fit sea-cliff retreat rates to mean annual wave power at each site, which we calculated from 30 yr hindcast wave data, we found a positive relationship between wave power and sea-cliff erosion, consistent with theoretical predictions and measurements on unlithified coastal bluffs. These comparisons provide field evidence that bedrock coastal erosion scales with wave power, offering a basis for modeling rocky coast evolution in different wave climates.

scholarly journals Comparing a thermo-mechanical Weichselian ice sheet reconstruction to GIA driven reconstructions: aspects of earth response and ice configuration

2013 ◽  
Vol 5 (2) ◽  
pp. 2345-2388 ◽  
Author(s):  
P. Schmidt ◽  
B. Lund ◽  
J-O. Näslund
Keyword(s):  
Sea Level ◽  
Ice Sheet ◽  
Younger Dryas ◽  
Slow Phase ◽  
Glacial Isostatic Adjustment ◽  
Relative Sea Level ◽  
Isostatic Adjustment ◽  
Earth Models ◽  
Uplift Rates ◽  
Best Fit

Abstract. In this study we compare a recent reconstruction of the Weichselian ice-sheet as simulated by the University of Main ice-sheet model (UMISM) to two reconstructions commonly used in glacial isostatic adjustment (GIA) modeling: ICE-5G and ANU (also known as RSES). The UMISM reconstruction is carried out on a regional scale based on thermo-mechanical modelling whereas ANU and ICE-5G are global models based on the sea-level equation. The Weichselian ice-sheet in the three models are compared directly in terms of ice volume, extent and thickness, as well as in terms of predicted glacial isostatic adjustment in Fennoscandia. The three reconstructions display significant differences. UMISM and ANU includes phases of pronounced advance and retreat prior to the last glacial maximum (LGM), whereas the thickness and areal extent of the ICE-5G ice-sheet is more or less constant up until LGM. The final retreat of the ice-sheet initiates at earliest time in ICE-5G and latest in UMISM, while ice free conditions are reached earliest in UMISM and latest in ICE-5G. The post-LGM deglaciation style also differs notably between the ice models. While the UMISM simulation includes two temporary halts in the deglaciation, the later during the Younger Dryas, ANU only includes a decreased deglaciation rate during Younger Dryas and ICE-5G retreats at a relatively constant pace after an initial slow phase. Moreover, ANU and ICE-5G melt relatively uniformly over the entire ice-sheet in contrast to UMISM which melts preferentially from the edges. We find that all three reconstructions fit the present day uplift rates over Fennoscandia and the observed relative sea-level curve along the Ångerman river equally well, albeit with different optimal earth model parameters. Given identical earth models, ICE-5G predicts the fastest present day uplift rates and ANU the slowest, ANU also prefers the thinnest lithosphere. Moreover, only for ANU can a unique best fit model be determined. For UMISM and ICE-5G there is a range of earth models that can reproduce the present day uplift rates equally well. This is understood from the higher present day uplift rates predicted by ICE-5G and UMISM, which results in a bifurcation in the best fit mantle viscosity. Comparison of the uplift histories predicted by the ice-sheets indicate that inclusion of relative sea-level data in the data fit can reduce the observed ambiguity. We study the areal distributions of present day residual surface velocities in Fennoscandia and show that all three reconstructions generally over-predict velocities in southwestern Fennoscandia and that there are large differences in the fit to the observational data in Finland and northernmost Sweden and Norway. These difference may provide input to further enhancements of the ice-sheet reconstructions.

Holocene isostasy and late Cenozoic development of landforms including Beaver and Radok Lake basins in the Amery Oasis, Prince Charles Mountains, Antarctica

1997 ◽  
Vol 9 (3) ◽  
pp. 299-306 ◽  
Author(s):  
D.A. Adamson ◽  
M.C.G. Mabin ◽  
J.G. Luly
Keyword(s):  
Sea Level ◽  
Late Cenozoic ◽  
Glacial Cycle ◽  
Ice Streams ◽  
Relative Sea Level ◽  
Field Evidence ◽  
North Eastern ◽  
Uplift Rates ◽  
Beaver Lake ◽  
Lambert Glacier

Geomorphological observations show no detectable uplift (i.e. falling relative sea level) of Amery Oasis since the establishment of relatively stable sea level during the mid-Holocene. The observations around the basin of Beaver Lake include an absence of raised shoreline features, the presence down to the present tidal limit of in situ ventifacts and residual landforms, the cliffed southern shoreline and adjacent shallow subhorizontal floor of Beaver Lake, and the composition of recent moraines on the basin's north eastern edge. This lack of Holocene uplift is consistent with low uplift rates observed from coastal oases of East Antarctica and suggests minor, rather than major, changes to the Antarctic ice sheet during the most recent Quaternary glacial cycle. The formation of Beaver basin is attributed to late Cenozoic glacial excavation by south flowing ice of the palaeo-Nemesis Glacier, initially eroding when relative sea level was higher than it is today. The basin containing Radok Lake was excavated by the palaeo-Battye Glacier probably when most effective during the numerous long cold periods of the late Cenozoic. The field evidence from landforms and the presence of marine fossil deposits suggests Amery Oasis was not overrun by erosive ice since at least the Pliocene, major ice streams such as Lambert Glacier flowing then, as now, around the oasis.

scholarly journals Sea-cliff Erosion with Rising Sea-Level along Shores Exposing Glacial Material in Atlantic Canada: The Effect of Bedrock Slope and an Example from Isle Madame, Nova Scotia

2013 ◽  
Vol 40 (1) ◽  
Author(s):  
Eric R. Force
Keyword(s):  
Nova Scotia ◽  
Sea Level ◽  
Limiting Factor ◽  
Atlantic Canada ◽  
Cliff Erosion ◽  
Coastal Retreat ◽  
Bedrock Surface ◽  
Sea Cliff ◽  
Le Canada ◽  
Rising Sea Level

Rapid retreat rates of sea cliffs exposing glacial material are a widespread problem, especially in Atlantic Canada, and one that will continue. Prediction of retreat rates at specific sites involves many variables, but a factor that has commonly been overlooked in such prediction is the slope of the bedrock surface under the glacial material. A glaciated bedrock platform is generally necessary to establish a stable situation of temporary equilibrium, and as sea-level rises, the bedrock slope determines the location of the new equilibrium position. An example from Nova Scotia shows that bedrock slope is so low on some coasts that the only long-range limiting factor is kinetic, i.e. how fast hydrodynamic energy can remove glacial material. Prediction of coastal retreat scenarios requires better information on the bedrock surface than is commonly available.SOMMAIRELes taux de retrait rapide des falaises qui exposent des matériaux glaciaires est un problème très répandu et qui va perdurer, surtout dans le Canada atlantique. La prévision des taux de retrait sur des sites spécifiques comporte de nombreuses variables et, la pente du substratum rocheux sur lequel reposent ces matériaux glaciaires et une variable qui a souvent été négligée. L’existence d’un substratum rocheux glacié est généralement une condition nécessaire pour l’établissement d’une situation d'équilibre stable temporaire, et lorsque le niveau de la mer monte, la pente du substratum rocheux a une influence déterminante sur le lieu de la nouvelle position d'équilibre. Un exemple en Nouvelle-Écosse montre que la pente du substratum rocheux est si faible sur certaines côtes que le seul facteur déterminant à long terme est la cinétique, c'est-à-dire la vitesse d’abrasion du matériau glaciaire correspondant à l’énergie hydrodynamique. La prévision des scénarios de retrait de la ligne côtière requière une meilleure connaissance du substratum rocheux. 

scholarly journals Multi-objective optimisation of a rock coast evolution model with cosmogenic <sup>10</sup>Be analysis for the quantification of long-term cliff retreat rates

2021 ◽  
Vol 9 (6) ◽  
pp. 1505-1529
Author(s):  
Jennifer R. Shadrick ◽  
Martin D. Hurst ◽  
Matthew D. Piggott ◽  
Bethany G. Hebditch ◽  
Alexander J. Seal ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Production Model ◽  
Relative Sea Level ◽  
Coastal Evolution ◽  
Radionuclide Production ◽  
Multi Objective ◽  
Cosmogenic Radionuclide ◽  
Cliff Retreat

Abstract. This paper presents a methodology that uses site-specific topographic and cosmogenic 10Be data to perform multi-objective model optimisation of a coupled coastal evolution and cosmogenic radionuclide production model. Optimal parameter estimation of the coupled model minimises discrepancies between model simulations and measured data to reveal the most likely history of rock coast development. This new capability allows a time series of cliff retreat rates to be quantified for rock coast sites over millennial timescales. Without such methods, long-term cliff retreat cannot be understood well, as historical records only cover the past ∼150 years. This is the first study that has (1) applied a process-based coastal evolution model to quantify long-term cliff retreat rates for real rock coast sites and (2) coupled cosmogenic radionuclide analysis with a process-based model. The Dakota optimisation software toolkit is used as an interface between the coupled coastal evolution and cosmogenic radionuclide production model and optimisation libraries. This framework enables future applications of datasets associated with a range of rock coast settings to be explored. Process-based coastal evolution models simplify erosional processes and, as a result, often have equifinality properties, for example that similar topography develops via different evolutionary trajectories. Our results show that coupling modelled topography with modelled 10Be concentrations can reduce equifinality in model outputs. Furthermore, our results reveal that multi-objective optimisation is essential in limiting model equifinality caused by parameter correlation to constrain best-fit model results for real-world sites. Results from two UK sites indicate that the rates of cliff retreat over millennial timescales are primarily driven by the rates of relative sea level rise. These findings provide strong motivation for further studies that investigate the effect of past and future relative sea level rise on cliff retreat at other rock coast sites globally.

Glacial Isostatic Adjustment with 3D Earth models: A comparison of case studies of deglacial relative sea level records of North America and Russian Arctic

2020 ◽  
Author(s):  
Tanghua Li ◽  
Nicole Khan ◽  
Simon Engelhart ◽  
Alisa Baranskaya ◽  
Peltier William ◽  
...  
Keyword(s):  
North America ◽  
Sea Level ◽  
3D Models ◽  
Viscosity Model ◽  
Glacial Isostatic Adjustment ◽  
Russian Arctic ◽  
Scaling Factors ◽  
Relative Sea Level ◽  
Isostatic Adjustment ◽  
Best Fit

&lt;p&gt;The Canadian landmass of North America and the Russian Arctic were covered by large ice sheets during the Last Glacial Maximum, and have been key areas for Glacial Isostatic Adjustment (GIA) studies. Previous GIA studies have applied 1D models of Earth&amp;#8217;s interior viscoelastic structure; however, seismic tomography, field geology and recent studies reveal the potential importance of 3D models of this structure. Here, using the latest quality-controlled deglacial sea-level databases from North America and the Russian Arctic, we investigate the effects of 3D structure on GIA predictions. We explore scaling factors in the upper mantle (&lt;em&gt;&amp;#946;&lt;sub&gt;UM&lt;/sub&gt;&lt;/em&gt;) and lower mantle (&lt;em&gt;&amp;#946;&lt;sub&gt;LM&lt;/sub&gt;&lt;/em&gt;) and the 1D background viscosity model (&lt;em&gt;&amp;#951;&lt;sub&gt;o&lt;/sub&gt;&lt;/em&gt;) with predictions of of the ICE-6G_C (VM5a) glaciation/deglaciation model of Peltier et al (2015, JGR) in these two regions, and compare with the best fit 3D viscosity structures.&lt;/p&gt;&lt;p&gt;We compute gravitationally self-consistent relative sea-level histories with time dependent coastlines and rotational feedback using both the Normal Mode Method and Coupled Laplace-Finite Element Method. A subset of 3D GIA models is found that can fit the deglacial sea-level databases for both regions. These databases cover both the near and intermediate field regions. However, North America and Russian Arctic prefer different 3D structures (i.e., combinations of (&lt;em&gt;&amp;#951;&lt;sub&gt;o&lt;/sub&gt;, &amp;#946;&lt;sub&gt;UM&lt;/sub&gt;, &amp;#946;&lt;sub&gt;LM&lt;/sub&gt;&lt;/em&gt;)) to provide the best fits. The Russian Arctic database prefers a softer background viscosity model (&lt;em&gt;&amp;#951;&lt;sub&gt;o&lt;/sub&gt;&lt;/em&gt;), but larger scaling factors (&lt;em&gt;&amp;#946;&lt;sub&gt;UM&lt;/sub&gt;, &amp;#946;&lt;sub&gt;LM&lt;/sub&gt;&lt;/em&gt;) than those preferred by the North America database.&lt;/p&gt;&lt;p&gt;Outstanding issues include the uncertainty of the history of local glaciation history. For example, preliminary modifications of the ice model in Russian Arctic reveal that the misfits of 1D models can be significantly reduced, but still fit less well than the best fit 3D GIA model.An additional issue concerns the extent to which the 3D models are able to improve both fits in North America and Russian Arctic when compared with 1D internal structure (ICE-6G_C VM5a &amp; ICE-7G VM7), will be assessed in a preliminary fashion.&lt;/p&gt;

Little Ice Age subsidence and post Little Ice Age uplift at Juneau, Alaska, inferred from dendrochronology and geomorphology

2003 ◽  
Vol 59 (3) ◽  
pp. 300-309 ◽  
Author(s):  
Roman J. Motyka
Keyword(s):  
Sea Level ◽  
Little Ice Age ◽  
18Th Century ◽  
Tide Gauge ◽  
Ice Age ◽  
Tide Gauge Records ◽  
Relative Sea Level ◽  
Late 18Th Century ◽  
Glaciomarine Sediments ◽  
Sea Cliff

AbstractApplication of dendrochronology and geomorphology to a recently emerged coastal area near Juneau, Alaska, has documented a Little Ice Age (LIA) sea-level transgression to 6.2 m above current sea level. The rise in relative sea level is attributed to regional subsidence and appears to have stabilized by the mid 16th century, based on a sea-cliff eroded into late-Pleistocene glaciomarine sediments. Land began emerging between A.D. 1770 and 1790, coincident with retreat of regional glaciers from their LIA maximums. This emergence has continued since then, paralleling regional glacier retreat. Total Juneau uplift since the late 18th century is estimated to be 3.2 m. The rate of downward colonization of newly emergent coastline by Sitka spruce during the 20th century closely parallels the rate of sea-level fall documented by analysis of local tide-gauge records (1.3 cm/yr). Regional and Glacier Bay LIA loading and unloading are inferred to be the primary mechanisms driving subsidence and uplift in the Juneau area. Climate change rather then regional tectonics has forced relative sea-level change over the last several hundred years.

Accelerated relative sea-level rise and rapid coastal erosion:

1997 ◽  
Vol 140 (3-4) ◽  
pp. 347-365 ◽  
Author(s):  
Jeffrey H List ◽  
Asbury H Sallenger ◽  
Mark E Hansen ◽  
Bruce E Jaffe
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Coastal Erosion ◽  
Relative Sea Level ◽  
Relative Sea Level Rise

scholarly journals Multi-objective optimisation of a rock coast evolution model with cosmogenic <sup>10</sup>Be analysis for the quantification of long-term cliff retreat rates

2021 ◽  
Author(s):  
Jennifer R. Shadrick ◽  
Martin D. Hurst ◽  
Matthew D. Piggott ◽  
Bethany G. Hebditch ◽  
Alexander J. Seal ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Production Model ◽  
Relative Sea Level ◽  
Coastal Evolution ◽  
Radionuclide Production ◽  
Multi Objective ◽  
Cosmogenic Radionuclide ◽  
Cliff Retreat

Abstract. This paper presents a methodology that uses site-specific topographic and cosmogenic 10Be data to perform multi-objective model optimisation of a coupled coastal evolution and cosmogenic radionuclide production model. Optimal parameter estimation of the coupled model minimises discrepancies between model simulations and measured data to reveal the most likely history of rock coast development. This new capability allows for a time-series of cliff retreat rates to be quantified for rock coast sites over millennial timescales. This is the first study that has 1) applied a process-based coastal evolution model to quantify long-term cliff retreat rates for real, rock coast sites, and 2) coupled cosmogenic radionuclide analysis with a process-based model. The Dakota optimisation software toolkit is used as an interface between the coupled coastal evolution and cosmogenic radionuclide production model and optimisation libraries. This framework enables future applications of datasets associated with a range of rock coast settings to be explored. Process-based coastal evolution models simplify erosional processes and, as a result, often have equifinality properties, for example, that similar topography develops via different evolutionary trajectories. Our results show that coupling modelled topography with modelled 10Be concentrations can reduce equifinality in model outputs. Furthermore, our results reveal that multi-objective optimisation is essential in limiting model equifinality caused by parameter correlation to constrain best-fit model results for real-world sites. Results from two UK sites indicate that the rates of cliff retreat over millennial timescales are primarily driven by the rates of relative sea level rise. These findings provide strong motivation for further studies that investigate the effect of past and future relative sea level rise on cliff retreat at other rock coast sites globally.

Submergence, nutrient enrichment, and tropical storm impacts on Spartina alterniflora in the microtidal northern Gulf of Mexico

2020 ◽  
Vol 644 ◽  
pp. 33-45
Author(s):  
JM Hill ◽  
PS Petraitis ◽  
KL Heck
Keyword(s):  
Gulf Of Mexico ◽  
Sea Level Rise ◽  
Sea Level ◽  
Spartina Alterniflora ◽  
Anthropogenic Impacts ◽  
Interactive Effects ◽  
Relative Sea Level ◽  
Hurricane Disturbance ◽  
Submergence Stress ◽  
Relative Sea Level Rise

Salt marshes face chronic anthropogenic impacts such as relative sea level rise and eutrophication, as well as acute disturbances from tropical storms that can affect the productivity of these important communities. However, it is not well understood how marshes already subjected to eutrophication and sea level rise will respond to added effects of episodic storms such as hurricanes. We examined the interactive effects of nutrient addition, sea level rise, and a hurricane on the growth, biomass accumulation, and resilience of the saltmarsh cordgrass Spartina alterniflora in the Gulf of Mexico. In a microtidal marsh, we manipulated nutrient levels and submergence using marsh organs in which cordgrasses were planted at differing intertidal elevations and measured the impacts of Hurricane Isaac, which occurred during the experiment. Prior to the hurricane, grasses at intermediate and high elevations increased in abundance. After the hurricane, all treatments lost approximately 50% of their shoots, demonstrating that added nutrients and elevation did not provide resistance to hurricane disturbance. At the end of the experiment, only the highest elevations had been resilient to the hurricane, with increased above- and belowground growth. Added nutrients provided a modest increase in above- and belowground growth, but only at the highest elevations, suggesting that only elevation will enhance resilience to hurricane disturbance. These results empirically demonstrate that S. alterniflora in microtidal locations already subjected to submergence stress is less able to recover from storm disturbance and suggests we may be underestimating the loss of northern Gulf Coast marshes due to relative sea level rise.

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