Tsunami deposits: Present knowledge and future challenges

Tsunami deposits are the primary source of information on (past) large tsunami events and thereby are crucial for accurate hazard assessments. Tsunami deposits studies have developed over the last three decades, but this is still a young geoscience discipline. Following the 5^th International Tsunami Field Symposium in 2017 an opportunity arose to publish a Special Issue focusing on present knowledge and future research challenges. This paper aims to briefly review current state-of-the-art research, summarizing major findings and gathering relevant works that describe the progress achieved over the last three decades. In this paper the relevance of tsunami deposits, their peculiar sedimentary characteristics and their differentiation from other high energy events are presented. Especially over the last decade an incredibly high number of studies have been published on tsunami deposits, many of which are of a high quality and provide detailed literature reviews. Some of these studies represent the current progress discussed here. Challenges are also introduced, to spur a discussion on future scientific questions that can and should be addressed by tsunami geoscientists. Coupling onshore–offshore records is an area where tsunami geoscience faces some of its major challenges. Moreover, the application of non-destructive high-resolution techniques to study the internal structure and composition of tsunami deposits can also provide an opportunity to further examine deposits, and from this derive physical parameters of the forcing mechanism. Another topic is better understanding of the erosional signature of tsunami events and a continuation of the effort to better incorporate age-estimation methods by developing more accurate dating methodology. Finally, there is also the need for the improvement of empirical, forward and regressive numerical models to better contribute to the characterization of tsunami events.     

Volcanic nutrient inputs and trophic state of Lake Caviahue,Patagonia, Argentina

The strategies for eutrophication control, remediation, and policy management are often defined for neutral to alkaline freshwater systems, as they are most suitable for human use. The influence of nutrients on eutrophication in a naturally-acidic lake is poorly known. The main purpose of the present work is to evaluate the significance of volcanic nutrients in the control of the trophic state of the acidic Lake Caviahue, located at North Patagonia, Argentina.     

SO2 Emission from Active Volcanoes Measured Simultaneously by COSPEC and mini-DOAS

We measured SO₂ emission rate from six volcanoes in Latin America (Santa Ana, El Salvador; San Cristóbal and Masaya, Nicaragua; Arenal and Poás, Costa Rica; Tungurahua and Sierra Negra, Ecuador) and from Mt. Etna, Italy, using two different remote sensing techniques: COSPEC (COrrelation SPECtrometer) and miniDOAS (miniaturized Differential Optical Absorption Spectroscopy). One of the goals of this study was to evaluate the differences in SO₂ emission rates obtained by these two methods. The observed average SO₂ emission rates measured during this study were 2688 t·d⁻¹ from Tungurahua in July 2006, 2375 t·d⁻¹ in September 2005 and 480 t·d⁻¹ in February 2006 from Santa Ana, 1200 t·d⁻¹ in May 2005 from Etna, 955 t·d⁻¹ in March 2006 and 1165 t·d⁻¹ in December 2006 from Masaya, 5400 t·d⁻¹ of March 7, 2006 and 265 t·d⁻¹ in March 2006 from San Cristobal, 113 t·d⁻¹ in April 2006 from Arenal, 104 t·d⁻¹ in April 2006 from Poás and 11 t·d⁻¹ in July 2006 from Sierra Negra volcano. Most of the observed relative differences of SO₂ emission measurements from COSPEC and miniDOAS were lower than 10%.     

Diffuse CO2 emission rate from Pululahua and the lake-filled Cuicocha calderas,Ecuador

We report herein the first results of two soil CO₂ efflux surveys carried out at Cuicocha lake-filled and Pululahua caldera volcanic systems, Ecuador. A total of 172 and 217 soil CO₂ efflux measurements were taken at the surface environment of Pululahua and Cuicocha calderas respectively, by means of the “accumulation chamber” method during the summer of 2006 to constrain the total CO₂ output from the studied area. Soil CO₂ efflux values ranged from non-detectable up to 48.5 and 141.7 g m^{− 2} d^{− 1} for Cuicocha and Pululahua calderas respectively. In addition, probability graphs were used to distinguish the existence of different geochemical populations. Sequential Gaussian Simulation was used to construct an average map for 100 simulations and to compute the total CO₂ emission at each studied area: 106 and 270 t d^{− 1} (metric tons per day) for Cuicocha (13.3 km²) and Pululahua (27.6 km²) volcanoes respectively.     

Comparative petroleum hydrocarbons levels and biochemical responses in mussels from hydrothermal vents (Bathymodiolus azoricus) and coastal environments (Mytilus galloprovincialis)

Aliphatic hydrocarbons and PAHs in the whole soft tissues of Bathymodiolus azoricus from three Mid-Atlantic Ridge hydrothermal vents (Menez-Gwen, Lucky Strike and Rainbow), and Mytilus galloprovincialis from three contaminated coastal sites in South Portugal were analysed, and its effects on the digestive gland microsomes mixed-function oxygenase system (MFO) were assessed. Aliphatic hydrocarbons levels were present in the same magnitude in both coastal and hydrothermal environments, while the UCM (unresolved complex mixture) for coastal mussels were higher than in vent mussels. In general, significantly higher PAHs concentrations were found in coastal mussels, compared to B. azoricus where low molecular weight PAHs (2-3 rings) represented the majority of PAHs contrarily to what was observed in M. galloprovincialis. The MFO components were present in both mussel species, and were detected in vent mussels for the first time. However this system seems to have different roles in species from these contrasting environments. In coastal mussels MFO responded to hydrocarbon contamination while response in hydrothermal organisms appeared to be related mainly to endogenous factors.     

Evaluation of weather forecast systems for storm surge modeling in the Chesapeake Bay

Accurate forecast of sea-level heights in coastal areas depends, among other factors, upon a reliable coupling of a meteorological forecast system to a hydrodynamic and wave system. This study evaluates the predictive skills of the coupled circulation and wind-wave model system (ADCIRC+SWAN) for simulating storm tides in the Chesapeake Bay, forced by six different products: (1) Global Forecast System (GFS), (2) Climate Forecast System (CFS) version 2, (3) North American Mesoscale Forecast System (NAM), (4) Rapid Refresh (RAP), (5) European Center for Medium-Range Weather Forecasts (ECMWF), and (6) the Atlantic hurricane database (HURDAT2). This evaluation is based on the hindcasting of four events: Irene (2011), Sandy (2012), Joaquin (2015), and Jonas (2016). By comparing the simulated water levels to observations at 13 monitoring stations, we have found that the ADCIR+SWAN System forced by the following: (1) the HURDAT2-based system exhibited the weakest statistical skills owing to a noteworthy overprediction of the simulated wind speed; (2) the ECMWF, RAP, and NAM products captured the moment of the peak and moderately its magnitude during all storms, with a correlation coefficient ranging between 0.98 and 0.77; (3) the CFS system exhibited the worst averaged root-mean-square difference (excepting HURDAT2); (4) the GFS system (the lowest horizontal resolution product tested) resulted in a clear underprediction of the maximum water elevation. Overall, the simulations forced by NAM and ECMWF systems induced the most accurate results best accuracy to support water level forecasting in the Chesapeake Bay during both tropical and extra-tropical storms.     

Better models are more effectively connected models

Water‐ and sediment‐transfer models are commonly used to explain or predict patterns in the landscape at scales different from those at which observations are available. These patterns are often the result of emergent properties that occur because processes of water and sediment transfer are connected in different ways. Recent advances in geomorphology suggest that it is important to consider, at a specific spatio‐temporal scale, the structural connectivity of system properties that control processes, and the functional connectivity resulting from the way those processes operate and evolve through time. We argue that a more careful consideration of how structural and functional connectivity are represented in models should lead to more robust models that are appropriate for the scale of application and provide results that can be upscaled. This approach is necessary because, notwithstanding the significant advances in computer power in recent years, many geomorphic models are still unable to represent the landscape in sufficient detail to allow all connectivity to emerge. It is important to go beyond the simple representation of structural connectivity elements and allow the dynamics of processes to be represented, for example by using a connectivity function. This commentary aims to show how a better representation of connectivity in models can be achieved, by considering the sorts of landscape features present, and whether these features can be represented explicitly in the model spatial structure, or must be represented implicitly at the subgrid scale. Copyright © 2017 John Wiley & Sons, Ltd.     

Spatial distribution of morphometric parameters of glacial cirques in the Central Pyrenees(Aran and Boí valleys)

Glacial cirques are typical landscape features of mid-latitude mountain environments like the Central Pyrenees. Their morphology as well as their spatial distribution provides insights about past glaciers and climates. In this study, we examine the distribution, morphometrical and topographical characteristics of glacial cirques in two U-shaped glacial valleys located in the Central Pyrenees – the Aran and the Boí valleys. They are located in different aspects of this mountain range(north vs south) under different climatic influences that promoted distinct glaciation patterns during the late Pleistocene. The spatial mapping of these landforms was carried out using high-resolution imagery and field observations. We analysed the data of the morphometrical and topographical variables of the glacial cirques by using different statistical and geospatial methods in order tounveil the factors controlling their formation and development. A total of 186 glacial cirques were mapped in the study area, including 119 in the Aran and 67 in the Boí valleys. The local topography and microclimate conditions lead to substantial differences in both areas in terms of the morphology and dimensions of the cirques. Glacial cirques in Boí are distributed at slightly higher elevations than in Aran and they are also larger, though their dimensions decrease with elevation in both valleys. Aran cirques are mostly oriented NE, while Boí landforms do not show any prevailing aspect. Even though lithology does not control the distribution of the glacial cirques, some specific lithological settings may favour the development of larger cirques. In general, glacial cirques in the Aran and the Boí valleys show morphometrical properties similar to those reported in other mid-latitude mountain ranges.