Simon Matthias May

Beachrock-type calcarenitic tsunamites along the shores of the eastern Ionian Sea (western Greece) – case studies from Akarnania, the Ionian Islands and the western Peloponnese

Th is paper presents geo-scientifi c evidence of beachrock-type calcarenitic tsunamites from three study areas in western Greece, namely from the Bays of Aghios Nikolaos (Akarnania), Langadakia (Cefalonia Island) and Aghios Andreas (Peloponnese). Geomorphological, sedimentological, micromorphological and geochemical studies were conducted to clarify depositional processes and the post-sedimentary evolution. Calcarenitic and locally conglomeratic carbonate crusts were studied in natural outcrops along the seafront and in vibracores. High-resolution topographic surveys and 3D-visualisation were carried out by diff erential GPS and LIDAR measurements. Tsunami impact was dated by a combined approach of radiocarbon, OSL and archaeological age determination and compared to local tsunami and earthquake chronologies. We found sedimentary structures such as basal unconformities, rip-up and intra-clasts, evidence of fi ning upward, thinning landward and upward increase in sorting as well as bi-to multimodal deposits and injection structures all of which are described as features typical of recent or historic tsunami deposits. Typically non-littoral sedimentary features such as load casts and convolute bedding further indicate gravity driven processes in water-saturated sheets of allochthonous deposits and are well known from, for example, turbidites. Moreover, thin section analyses revealed highenergy shockand impact-borne cracking and shearing eff ects. Our results show that cementation of tsunami deposits may occur by post-depositional pedogenetic decalcifi cation of higher sections and subsequent secondary carbonate precipitation in lower sections of tsunami deposits provided that they were deposited above sea level. Th e calcarenitic tsunamites encountered in the three study areas match the defi nition of beachrock sensu stricto. Th is is thus the fi rst paper giving examples of beachrock sequences that are interpreted as partially cemented tsunami deposits. Consequently, beachrock is recommended not to be used as sea level indicator in future studies unless a tsunamigenic formation can be defi nitely excluded. Dating results brought to light young, mostly Holocene ages of tsunami sediments. In the Bay of Aghios Andreas, western Peloponnese, we found spectacular traces that Olympia’s ancient harbour site Pheia was destroyed by tsunami impact in the 6th cent. AD and covered by a rapidly cemented, up to 3 m-thick beachrock-type tsunami deposit.

Coastal hazards from tropical cyclones and extratropical winter storms based on holocene storm chronologies

Aware of past and future climate changes, the question arose whether modern instrumental data adequately reflect the chronology of tropical cyclones and extratropical winter storms for the period of the present eustatic sea level highstand (approx. the past 6,000 years). For pre-instrumental times, geological and sedimentological methods have been applied at geo- and bioarchives such as coastal marshes, lagoons, washover features or beach ridges, showing a frequency of strong cyclones roughly every 100–300 years, which is in contrast to the high number of major cyclones recorded recently. Many of these palaeotempestological records are discontinuous or contain hiatuses and it may be difficult to evaluate whether these sections of the record represent quiet phases without major cyclones or simply erosion or fluctuations in the ability of an archive to record the signature of cyclones. Manifold questions are still unanswered: as the potential number of former cyclones may be stored in landforms and sediments, how can the intensity of these cyclones be identified? Is the crest height of beach ridges a good indicator for storm surge heights, air pressure, and cyclone categories? This paper reviews important achievements in palaeotempestology and discusses open questions of cyclone distribution, frequency and energy (i.e., hazard potential) in the last few decades and reconstructions of these parameters back into Mid-Holocene times.

The Gyra washover fan in the Lefkada Lagoon, NW Greece—possible evidence of the 365 AD Crete earthquake and tsunami

Coastal geomorphological and geological archives store valuable information about the geodynamic evolution of coastal areas and the contributing geomorphodynamic processes. The coastal geomorphology of the Lefkada– Preveza coastal zone, NW Greece, holds evidence for the influence of both gradual, low-energy and episodic, high-energy coastal processes. Situated close to the Hellenic Arc and the Cefalonia transform fault, the area belongs to one of the seismically most active regions in the Mediterranean. Thus, tsunami events are assumed to have contributed to the coastal evolution in the study area according to tsunami catalogues and field evidence from previous investigations. The northern part of the Lefkada Lagoon, separated from the Ionian Sea by an extensive barrier beach system, is characterized by a number of fan-like washover structures, formed by different washover generations. In this paper, we present detailed geomorphological, sedimentological, geochemical and foraminiferal investigations on the most prominent fan structure, the Gyra fan, based on terrestrial and lagoonal sediment cores. The Gyra fan consists of a coarse-grained sequence of fully marine origin on top of lagoonal mud and a palaeosol, respectively. The sequence shows numerous characteristics of extreme wave deposits. Due to the dimension and morphology of the fan, the existence of up to four consistent and correlative stratigraphic subunits, their landward thinning and their comparable sedimentary characteristics, we argue that a tsunami event induced the formation of the Gyra fan, comprising at least four major inundation impulses. According to radiocarbon dates, this geomorphological structure was most likely formed by teletsunami effects triggered by the 365 AD earthquake off western Crete.

Shoreline changes and high-energy wave impacts at the leeward coast of Bonaire (Netherlands Antilles)

Supralittoral coarse-clast deposits along the shores of Bonaire (Netherlands Antilles) as well as increased hurricane frequency during the past decade testify to the major hazard of high-energy wave impacts in the southern Caribbean. Since deducing certain events from the subaerial coarse-clast record involves major uncertainties and historical reports are restricted to the past 500 years, we use a new set of vibracore and push core data (i) to contribute to a more reliable Holocene history of regional extreme-wave events and (ii) to evaluate their impact on shoreline evolution. Multi-proxy palaeoenvironmental analyses (XRF, XRD, grain size distribution, carbonate, LOI, microfossils) were carried out using nearshore sedimentary archives from the sheltered western (leeward) side of Bonaire and its small neighbour Klein Bonaire. In combination with 14C-AMS age estimates the stratigraphy reflects a long-term coastal evolution controlled by relative sea level rise, longshore sediment transport, and short-term morphodynamic impulses by extreme wave action, all three of which may have significantly influenced the development of polyhaline lagoons and the demise of mangrove populations. Extreme wave events may be categorized into major episodic incidents (c. 3.6 ka [?] BP; 3.2–3.0 ka BP; 2.0–1.8 ka BP; post-1.3 ka [?] BP), which may correspond to tsunamis and periodic events recurring on the order of decades to centuries, which we interpret as severe tropical cyclones. Extreme wave events seem to control to a certain extent the formation of coastal ridges on Bonaire and, thus, to cause abrupt shifts in the long-term morphodynamic and ecological boundary conditions of the circumlittoral inland bays.

Life and death after super typhoon Haiyan

Super typhoon Haiyan, packing sustained winds >300 kph, wrought immense damage on the Philippines in November 2013. Haiyan displaced large boulders in some areas (Engel et al. 2014) and generated an estimated 5 m surge in the Sagay Marine Reserve (10 58¢57.58†N, 123 27¢50.00†E), central Philippines. Immediately after, a coral boulder and rubble ridge several hundred meters long was exposed at low tide on Carbin Reef within the reserve (Fig. 1a). It was either newly established or heightened by the typhoon, but the presence of at least two different depositional units of rubble suggests the latter may be more likely. We present an exhibition of extremes: a heavily damaged subtidal reef area (Fig. 1b) and a largely untouched intertidal coral community (Fig. 1c) separated only by the 20 m-wide ridge. On Carbin’s western slope, the typhoon displaced boulders, sheared stands of Heliopora, and overturned massive colonies down to 10 m. Landwards of the ridge, in the shallow intertidal, many branching acroporids and massive faviids and poritids remained alive and structurally intact, consistent with observations and model predictions of Hongo et al. (2012). Haiyan maystill take its tollhere, however.ByFebruary 2014, partial mortality was evident on the tips of some branching acroporids where they remain above water at low tide. Future surveys will document if the newly established or significantly heightened ridge wrought physical/ hydrological changes that could cause delayed mortality (HarmelinVivien 1994). However, the observable immediate effects of super typhoon Haiyan on Carbin demonstrate that even a category five storm is not a universal death sentence for corals in shallow habitats. Local geomorphology, exposure, and sediment dynamics merit consideration in assessing storm vulnerability, even in the shallowest of reef areas.

Holocene sea levels of Bonaire (Leeward Antilles) and tectonic implications

Summary. Future relative sea-level (RSL) rise is one of the most serious coastal hazards worldwide, in particular in the Caribbean region. RSL is a function of global (glacioeustasy, steric effect), regional (e.g. glacioisostatic adjustment [GIA], gravitational effects inducing deformation of the earth, upper/lower mantle viscosity, etc.) and local (lithosome compaction, vertical neotectonic movement) factors which are connected via a complex pattern of interference. Information on past RSL supports inferences on upper limits of ice shield ablation, estimates of anthropogenic contribution to historical and future RSL rise and calibration of rheological models of the earth. We present the first RSL curve for the island of Bonaire (S Caribbean). Forty-two 14 C ages from 20 sediment cores taken from nine different sedimentary archives along the coast were used. The sedimentary environment of each index point was linked to a palaeowater depth based on literature and field observations. The index points trace a local RSL history of decelerating rise since 7000-6000 years ago and subsequent asymptotical approximation, similar to existing RSL curves from Curaςao and Venezuela. The results were compared to a simulation of Holocene sea-level history (reference model) which considers global effects and regional GIA (including consequences for geopotential and vertical position of earth surface). Even though the central and NW parts of Bonaire experienced slow tectonic uplift of up to 50 cm since the mid-Holocene and tentative correction for compaction was applied, the new RSL curve for Bonaire runs slightly below the reference model. A further outcome of this study is the detection of an unmapped micro-graben structure with a vertical slip rate of c. 1.5 mm yr -1 at Boka Bartol, which was identified based on depth discrepancies of well-dated isochronous highenergy wave deposits. Zusammenfassung. Der zukunftige relative Meeresspiegelanstieg stellt eines der gravierendsten Kustenrisiken weltweit dar, dies gilt insbesondere fur den karibischen Raum. Der relative Meeresspiegel ist eine Funktion globaler (Glazialeustasie, sterischer Effekt), regionaler (z. B. Glazialisostasie, gravitative Effekte und deren Einfluss auf die Deformation der Asthenosphare, Dynamik der Asthenospharenviskositat) und lokaler (Sedimentkompaktion, vertikale tektonische Bewegungen) Faktoren, die wiederum uber ein komplexes Netzwerk von Wechselwirkungen verbunden sind. Die Rekonstruktion lokaler Meeresspiegelhistorien ermoglicht Ruckschlusse auf maximale postglaziale Ablationswerte der Eisschilde, den anthropogenen Einfluss auf den historischen und zukunftigen relativen Meeresspiegelanstieg, und dient daruber hinaus der Kalibrierung rheologischer Modelle. Diese Studie prasentiert die erste relative Meeresspiegelkurve der Insel Bonaire (Sud-Karibik), deren Basis aus 42 14 C-Altern aus 20 Sedimentkernen von neun unterschiedlichen Sedimentarchiven entlang der Kuste besteht. Der umgebenden Fazies eines jeden datierten Objekts wurde auf Basis von Literaturwerten und Gelandebeobachtungen eine Palao-Wassertiefe zugewiesen. Die Resultate deuten auf einen sich seit 7000-6000 Jahren vor heute verlangsamenden Meeresspiegelanstieg und eine damit verbundende asymptotische Annaherung an das heutige Niveau hin, ahnlich der bereits existierenden relativen

Using Benford’s law to investigate natural hazard dataset homogeneity

Working with a large temporal dataset spanning several decades often represents a challenging task, especially when the record is heterogeneous and incomplete. The use of statistical laws could potentially overcome these problems. Here we apply Benford’s Law (also called the “First-Digit Law”) to the traveled distances of tropical cyclones since 1842. The record of tropical cyclones has been extensively impacted by improvements in detection capabilities over the past decades. We have found that, while the first-digit distribution for the entire record follows Benford’s Law prediction, specific changes such as satellite detection have had serious impacts on the dataset. The least-square misfit measure is used as a proxy to observe temporal variations, allowing us to assess data quality and homogeneity over the entire record, and at the same time over specific periods. Such information is crucial when running climatic models and Benford’s Law could potentially be used to overcome and correct for data heterogeneity and/or to select the most appropriate part of the record for detailed studies.

Coastal environments from polar regions to the tropics: a geographer’s zonality perspective

Abstract From a geographical point of view, the general pattern of coastal zones (or geographical coastal zonality) is arranged along latitudinal gradients and gradations from the Equator to the poles, caused by the spherical shape of our planet and the distribution of heat according to the angle of incoming radiation. As the distribution of land and oceans differs between hemispheres and along latitudes, and atmospheric and oceanic circulation moves energy in all directions, the global pattern of coastal forms and processes due to climate-triggered conditions is very complex. Moreover, each single pattern is dynamic and subject to revision by changes in the climate. Some coastal zones (e.g. humid tropics or high polar zones) can be delimited rather easily, while others (e.g. temperate cool or those with alternating tropical climate) are more difficult to define. This paper provides a short overview of the state of the art in geographical zonality of coastal environments (not only of coastlines) from the poles to the Equator, with the main emphasis on cold and warm zones, pointing to climate-induced differences in the context of Quaternary climate change or those occurring over the last centuries and decades.

Drone photogrammetry and KMeans point cloud filtering to create high resolution topographic and inundation models of coastal sediment archives: Drone photogrammetry point cloud filtering

Coastal areas are vulnerable to the impacts of tropical cyclones (TC), tsunamis and other water super-elevation events, but the frequency of these events is often poorly represented by conventional records. Coastal overwash deposits (including washover fans) can provide a longer-term archive of event frequency. Because of their low-gradient geomorphic form, washover fans require high accuracy (centimetre-resolution) topographic models to understand patterns of connectivity and dynamics that control archive formation. Using images collected by a remotely piloted aircraft system (RPAS, or ‘drone’) and Structure-from-Motion (SfM) photogrammetry techniques, we apply a novel point-cloud filtering technique based on KMeans classification of the R-G-B colour of each X-Y-Z point to remove vegetation and create a centimetre-resolution and accuracy bare-earth digital terrain model (DTM) of a washover fan in Exmouth Gulf (Western Australia). Using the RPAS-SfM orphophoto and DEM data, supported by ground-penetrating radar (GPR) and field stratigraphic analysis, we show how this approach can be applied to understand dynamics controlling low-gradient geomorphic landforms, using an example of a washover fan sedimentary archive in northwestern Australia created by extreme overwash events. Our approach reveals the likely role of backflooding and terrestrial runoff in creating backwater environment for sub-aqueous deposition and good sediment preservation and identifies key areas to target for detailed dating and stratigraphic analysis of a potentially decadal to sub-millennial resolution sediment archive of TC activity. Copyright

Late Quaternary stratigraphy of the La Janda Basin (SW Spain) - first results and palaeoenvironmental significance

The La Janda basin in southern Spain is a near-shore geo-bio-archive comprising a variable Quaternary depositional history, with shallow marine, lacustrine, palustrine, and terrestrial strata. In the 1930s the lake was drained and is serving now as a huge agricultural area. The 33 m-core recovered in fall 2016 along with several shallower drill cores up to c. 15 m, reveals insights into a unique mixed terrestrial palaeo-environmental archive in Andalucia influenced by the Atlantic Ocean and hence the North Atlantic Oscillation (NAO) within the Gulf of Cadiz. The basins evolution was influenced both by the postglacial marine transgression and by an active tectonic fault controlling most of the accommodation space by causing subsidence. Our long core was accompanied by further corings along an E-W striking transect in order to reveal also the relation of the influence of tectonic activity with sedimentary sequences. Multi-Sensor Core Logging has been completed. Results of sedimentological, geochemical and micropalaeontological analyses will be presented in the frame of the climate variations during the Late Pleistocene and the Holocene, along with a preliminary age-depth model based on radiocarbon (AMS-14C) and optical stimulated luminescence (OSL) dating techniques. Our investigations ultimately aim at providing valuable information on major Late Pleistocene to Holocene climatic and palaeo-environmental fluctuations in the southernmost part of the Iberian Peninsula.