Tsunamis on the Pacific Coast of Canada Recorded in 1994–2007

In the last 15 years there have been 16 tsunami events recorded at tide stations on the Pacific Coast of Canada. Eleven of these events were from distant sources covering almost all regions of the Pacific, as well as the December 26, 2004 Sumatra tsunami in the Indian Ocean. Three tsunamis were generated by local or regional earthquakes and two were meteorological tsunamis. The earliest four events, which occurred in the period 1994–1996, were recorded on analogue recorders; these tsunami records were recently re-examined, digitized and thoroughly analysed. The other 12 tsunami events were recorded using digital high-quality instruments, with 1-min sampling interval, installed on the coast of British Columbia (B.C.) in 1998. All 16 tsunami events were recorded at Tofino on the outer B.C. coast, and some of the tsunamis were recorded at eight or more stations. The tide station at Tofino has been in operation for 100 years and these recent observations add to the dataset of tsunami events compiled previously by S.O. Wigen (1983) for the period 1906–1980. For each of the tsunami records statistical analysis was carried out to determine essential tsunami characteristics for all events (arrival times, maximum amplitudes, frequencies and wave-train structure). The analysis of the records indicated that significant background noise at Langara, a key northern B.C. Tsunami Warning station located near the northern end of the Queen Charlotte Islands, creates serious problems in detecting tsunami waves. That station has now been moved to a new location with better tsunami response. The number of tsunami events observed in the past 15 years also justified re-establishing a tide gauge at Port Alberni, where large tsunami wave amplitudes were measured in March 1964. The two meteorological events are the first ever recorded on the B.C. coast. Also, there have been landslide generated tsunami events which, although not recorded on any coastal tide gauges, demonstrate, along with the recent investigation of a historical catastrophic event, the significant risk that landslide generated tsunami pose to coastal and inland regions of B.C.     

Nicholas Crisp's “Porcellien”: A petrological comparison of sherds from the Vauxhall (London; ca. 1751–1764) and Indeo Pottery (Bovey Tracey,Devonshire; ca. 1767–1774) factory sites

The character of porcelain wares made by Nicholas Crisp early and late in his career was assessed using microchemical and petrographic data for sherds excavated from the sites of the factories he operated at Vauxhall and Bovey Tracey. The results indicate that, over time, Crisp increasingly made use of diverse types of pastes as he struggled to produce a commercially viable line of porcelain. Based on the analysis of a limited number of samples, he appears to have largely restricted himself at Vauxhall to using soapstone (Mg‐rich)‐ and flint‐glass (Pb‐rich) frit‐bearing pastes that varied in the amount of calcite they contained. He also experimented with Mg+Pb‐rich pastes at Bovey Tracey, but included a novel ingredient (barite) and varied the proportion of other minor constituents (e.g., bone ash), apparently in an effort to resolve some of the firing problems that plagued him at Vauxhall. In addition, Crisp appears to have produced bone ash (phosphatic) porcelain at Bovey Tracey, and, in collaboration with William Cookworthy, the proprietor of the Plymouth factory, fired a range of true porcelain (Si+Al‐rich) pastes. Bulk compositional data indicate that Crisp's diopside‐bearing Mg+Pb‐rich wares were derived from pastes containing talc and calcite rather than dolomite. The mineralogy of these and some contemporary magnesian/plombian porcelains are interpreted using the SiO₂‐CaO‐MgO phase diagram. This diagram shows that these wares can form and preserve diopside (Ca‐Mg silicate) given suitable bulk CaO contents and kiln‐firing temperatures. Phosphatic sherds from Bovey Tracey are compositionally distinct (lower SiO₂ and higher Al₂O₃ and bone‐ash components) from a single bone‐ash sample from Vauxhall, indicating that Crisp experimented with novel bone‐ash pastes, and was not positively influenced by the Vauxhall phosphatic recipe, if indeed one existed. True porcelains from Bovey Tracey have more extreme SiO₂/Al₂O₃ ratios (= 2.0 [two sherds]; 4.5 [one sherd]) than their Plymouth/Bristol counterparts (SiO₂/Al₂O₃ = 2.3–3.0). Collectively, the analytical data underscore the experimental—and ultimately unsuccessful—character of the diverse wares produced by Nicholas Crisp. © 2000 John Wiley & Sons, Inc.     

Wave transformation across a macrotidal shore platform under low to moderate energy conditions

We investigate how waves are transformed across a shore platform as this is a central question in rock coast geomorphology. We present results from deployment of three pressure transducers over four days, across a sloping, wide (~200 m) cliff‐backed shore platform in a macrotidal setting, in South Wales, United Kingdom. Cross‐shore variations in wave heights were evident under the predominantly low to moderate (significant wave height < 1.4 m) energy conditions measured. At the outer transducer 50 m from the seaward edge of the platform (163 m from the cliff) high tide water depths were 8+ m meaning that waves crossed the shore platform without breaking. At the mid‐platform position water depth was 5 m. Water depth at the inner transducer (6 m from the cliff platform junction) at high tide was 1.4 m. This shallow water depth forced wave breaking, thereby limiting wave heights on the inner platform. Maximum wave height at the middle and inner transducers were 2.41 and 2.39 m, respectively, and significant wave height 1.35 m and 1.34 m, respectively. Inner platform high tide wave heights were generally larger where energy was up to 335% greater than near the seaward edge where waves were smaller. Infragravity energy was less than 13% of the total energy spectra with energy in the swell, wind and capillary frequencies accounting for 87% of the total energy. Wave transformation is thus spatially variable and is strongly modulated by platform elevation and the tidal range. While shore platforms in microtidal environments have been shown to be highly dissipative, in this macro‐tidal setting up to 90% of the offshore wave energy reached the landward cliff at high tide, so that the shore platform cliff is much more reflective. Copyright © 2017 John Wiley & Sons, Ltd.     

Markov chain Monte Carlo (MCMC) sampling methods to determine optimal models,model resolution and model choice for Earth Science problems

We present an overview of Markov chain Monte Carlo, a sampling method for model inference and uncertainty quantification. We focus on the Bayesian approach to MCMC, which allows us to estimate the posterior distribution of model parameters, without needing to know the normalising constant in Bayes' theorem. Given an estimate of the posterior, we can then determine representative models (such as the expected model, and the maximum posterior probability model), the probability distributions for individual parameters, and the uncertainty about the predictions from these models. We also consider variable dimensional problems in which the number of model parameters is unknown and needs to be inferred. Such problems can be addressed with reversible jump (RJ) MCMC. This leads us to model choice, where we may want to discriminate between models or theories of differing complexity. For problems where the models are hierarchical (e.g. similar structure but with a different number of parameters), the Bayesian approach naturally selects the simpler models. More complex problems require an estimate of the normalising constant in Bayes' theorem (also known as the evidence) and this is difficult to do reliably for high dimensional problems. We illustrate the applications of RJMCMC with 3 examples from our earlier working involving modelling distributions of geochronological age data, inference of sea-level and sediment supply histories from 2D stratigraphic cross-sections, and identification of spatially discontinuous thermal histories from a suite of apatite fission track samples distributed in 3D.     

Development of a brownfield inventory for prioritizing funding outreach in Tucson,Arizona

Fear of liability from the 1980 Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA or Superfund) has prompted developers to build pre...     

A comparison of global tropospheric teleconnections using observed satellite and general circulation model total ozone column data for 1979–91

 The total ozone column is well correlated with tropospheric fields such as the heights of the upper tropospheric geopotential surfaces and thus it can provide useful information on temporal variability in the troposphere. The global availability of long period satellite measurements of the total ozone column, taken by the TOMS instruments since 1978, provides a valuable and independent data set for use in studies of seasonal and interannual climate variability. In this study, the global low-frequency seasonal teleconnections in the observed TOMS data from 1979–91 have been investigated using seasonal teleconnectivity maps and empirical orthogonal function analysis. They have also been compared with the results from a simulation made with the atmospheric GCM at Météo-France, having prescribed observed sea surface temperatures for the same period. In the observed total ozone, strong ENSO-related wave number one longitudinal dipole patterns are seen in both the tropics and in the Southern Hemisphere extratropics. The model shows much weaker variability in total ozone yet appears to be able to capture similar teleconnection patterns in the tropics related to ENSO. In the SH extratropics, the model total ozone shows a strong wave number 3 response rather than the wave number one dipole seen in the observations. A wave number 3 response is also evident in the 200 hPa geopotential height simulated by the model and in the NCEP analysis, and is consistent with the response in a linearised barotropic model forced in the Indonesian region. The different responses in the modelled and observed total ozone, suggest that tropopause effect is not the major factor in the SH extratropics, and it is likely that horizontal ozone transport also plays a role in this region. Despite a generally poor simulation of the zonal mean total ozone, the model was able to capture the anomalous strengthening of the SH stationary waves during austral spring of 1988, related to an intense stratosphere sudden warming. Received: 21 October 1996 / Accepted: 11 September 1997     

Does increasing the spatial resolution of a regional climate model improve the simulated daily precipitation?

Three different resolution (50, 12, and 1.5 km) regional climate model simulations are compared in terms of their ability to simulate moderate and high daily precipitation events over the southern United Kingdom. The convection-permitting 1.5-km simulation is carried out without convective parametrisation. As in previous studies, increasing resolution (especially from 50 to 12 km) is found to improve the representation of orographic precipitation. The 50-km simulation underestimates mean precipitation over the mountainous region of Wales, and event intensity tends to be too weak; this bias is reduced in both the 12- and 1.5-km simulations for both summer and winter. In south–east England lowlands where summer extremes are mostly convective, increasing resolution does not necessary lead to an improvement in the simulation. For the 12-km simulation, simulated daily extreme events are overly intense. Even though the average intensity of summer daily extremes is improved in the 1.5-km simulation, this simulation has a poorer mean bias with too many events exceeding high thresholds. Spatial density and clustering of summer extremes in south–east England are poorly simulated in both the 12- and 1.5-km simulations. In general, we have not found any clear evidence to show that the 1.5-km simulation is superior to the 12-km simulation, or vice versa at the daily level.     

Effect of ionic strength on the Mg content of calcite: Toward a physical basis for minor element uptake during step growth

This experimental study determined the effect of ionic strength (IS) on the uptake of Mg into calcites that grew by the classical step propagation process. Using flow-through AFM and defined solution chemistry, calcite was grown in NaCl and KCl solutions of known supersaturation state while measuring the corresponding growth kinetics. Analysis of the resulting calcite compositions by SIMS shows that Mg content is inversely correlated with IS for both electrolytes. A sixfold increase in IS decreases the Mg-content by up to 40%. Overgrowths that developed in NaCl solutions contain more Mg than samples that grew in KCl solutions. The corresponding kinetic measurements reveal that step propagation rates are independent of IS within experimental error but are electrolyte-specific. In NaCl solutions, steps with the obtuse geometry move significantly faster than acute steps, but in KCl solutions, the acute and obtuse steps move at similar rates.Analysis of the data suggests that the decrease in Mg content with increasing IS arises from the interplay of ion-kink interactions between the background cations (Na⁺ or K⁺), the primary solute cation (Ca²⁺), and the impurity (Mg²⁺). A simple physical model proposes that increasing levels of electrolytes block the attachment of the strongly hydrated Mg²⁺ ion relative to Ca²⁺ but the effects are step-specific for each type of electrolyte. Whereas K⁺ interacts weakly with kink sites along both step directions, Na⁺ interacts preferentially with acute steps and, consequently, slows their rate of step propagation relative to obtuse steps. Because Na⁺ increases the fraction of the surface that develops from acute steps and because Mg is preferentially incorporated into the kink sites of acute steps, calcite overgrowths developed in NaCl solutions contain more Mg than those in grown in KCl. Thus, the salt-specific Mg contents measured in this study can be explained by shifts in the distribution of step types and the ability of each step type to incorporate Mg. The findings reconcile apparent discrepancies regarding the effect of IS on calcite kinetics and Mg incorporation observed in laboratory-based studies.     

Rip current escape strategies: lessons for swimmers and coastal rescue authorities

Lagrangian flow of two rip currents was measured using human drifters to understand how variations in surf zone circulation affect exit positions of floating swimmers. Based on these results, two escape strategies were assessed, ‘do nothing’ and ‘swim parallel to the beach’. The drifter paths and exit positions were analysed to determine the best escape strategy for passive swimmers in each scenario. Of the two methods, doing nothing to allow the rip current to take a swimmer is the most effective strategy. More than 75% of rip current flow scenarios could hinder chances of escape of swimmers if the wrong direction was chosen to swim parallel to the beach to safety. This is because in many situations a swimmer encounters not only a rip current flowing offshore but also a longshore current flowing parallel to the beach. The best education campaign for the public, in addition to only swimming on a patrolled beach, would be to promote the ‘do nothing’ rip current escape strategy, as it covers all flow scenarios without reducing a swimmer’s chance of survival.     

The relationship between winter lake cover,radiation receipts and the oxygen deficit in temperate lakes

Abstract

The composition, timing and duration of winter lake cover are shown to produce significant spatial and temporal variations in the radiation received at the surface of the water column, and are linked to the timing and rate of oxygen depletion of a temperate lake. In particular, the first snowfall to accumulate on the ice cover reduces radiation input to nearly zero and coincides with the initiation of the linear phase of oxygen depletion. Ablation of the snow cover in spring results in increased radiation receipts and oxygen levels. A simple model shows that the conversion of snow to white ice, which normally occurs during the midwinter period, increases radiation receipts and oxygen levels. Manipulation of the cover by artificially induced slushing is suggested as a management technique in the control of winter oxygen deficits.