Global distribution of coastal cliffs

Previous studies have estimated that coastal cliffs exist on about 80% of the global shoreline, but have not been validated on a global scale. This study uses two approaches to capture information on the worldwide existence and erosion of coastal cliffs: a detailed literature survey and imagery search, and a GIS-based global mapping analysis. The literature and imagery review show coastal cliffs exist in 93% of the combined recognized independent coastal states and non-independent coastal regions worldwide (total of 213 geographic units). Additionally, cliff retreat rates have been quantified in at least one location within 33% of independent coastal states and 15% of non-independent regions. The GIS-based mapping used the near-global Shuttle Radar Topography Mission 3 arc second digital elevation model and Arctic Coastal Dynamics Database to obtain near-global backshore coastal elevations at 1 km alongshore intervals comprising about 1,340,000 locations (81% of the world vector shoreline). Backshore coastal elevations were compared with the mapped distribution of European coastal cliffs to produce a model training set, and this relationship was extended globally to map the likelihood of coastal cliff locations. About 21% of the transects (17% of the world vector shoreline) were identified as mangroves and eliminated as potential cliff locations. The results were combined with estimates of cliff percentages for Greenland and Antarctica from the literature, extending the global coverage to estimate cliff occurrence across 89% of the world vector shoreline. The results suggest coastal cliffs likely exist on about 52% of the global shoreline. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

Constraining sediment provenance for tsunami deposits using distributions of grain size and foraminifera from the Kujukuri coastline and shelf,Japan

Tsunami deposits preserved in the geological record provide a more comprehensive understanding of their patterns of frequency and intensity over longer timescales; but recognizing tsunami deposits can prove challenging due to post-depositional changes, lack of contrast between the deposits and surrounding sedimentary layers, and differentiating between tsunami and storm deposition. Modern baseline studies address these challenges by providing insight into modern spatial distributions that can be compared with palaeotsunami deposits. This study documents the spatial fingerprint of grain size and foraminifera from Hasunuma Beach and the Kujukuri shelf to provide a basis from which tsunami deposits can be interpreted. At Hasunuma Beach, approximately 50 km east of Tokyo, the spatial distribution of three common proxies (foraminiferal taxonomy, foraminiferal taphonomy and sediment grain size) for tsunami identification were mapped and clustered using Partitioning Around Medoids cluster analysis. Partitioning Around Medoids cluster analysis objectively discriminated two coastal zones corresponding to onshore and offshore sample locations. Results show that onshore samples are characterized by coarser grain sizes (medium to coarse sand) and higher abundances of Pararotalia nipponica (27 to 63%) than offshore samples, which are characterized by finer grain sizes (fine to medium sand), lower abundances of Pararotalia nipponica (2 to 19%) and Ammonia parkinsoniana (0 to 10%), higher abundances of planktonics (15 to 58%) and species with fragile tests including Uvigerinella glabra. When compared to grain-size and foraminiferal taxonomy, foraminiferal taphonomy; i.e. surface condition of foraminifera, a proxy not commonly used to identify tsunami deposits, was most effective in discriminating modern coastal zones (identified supratidal, intertidal and offshore environments) and determining sediment provenance for tsunami deposits at Kujukuri. This modern baseline study assists the interpretation of tsunami deposits in the geological record because it provides a basis for sediment provenance to be determined.     

Spatiotemporal variability of vegetation due to drought dynamics (2012–2017): a case study of the Upper Paraíba River basin,Brazil

Natural Hazards - Vegetation indices have been widely used for monitoring the spatiotemporal variables of vegetation and characterizing droughts, primarily in semiarid regions. Drought is a...     

Recent and historical tsunami deposits from Lake Tokotan,eastern Hokkaido,Japan, inferred from nondestructive,grain size,and radioactive cesium analyses

Geological evidence of recent tsunamis from sediment samples collected from Lake Tokotan, a coastal lagoon in eastern Hokkaido, northern Japan, was detected using computed tomography (CT) and soft X-ray images, grain size, and radionuclide profiles. Initial field observations revealed that sediments had no discernable sedimentary structures at the top of the core. However, results of CT imaging, soft X-ray, and grain size analyses show evidence for three invisible sand layers that are intercalated with mud layers. These sand layers exhibit trends of landward fining and thinning. Furthermore, the distribution of sand layers was limited to the center and seaward parts of the lake. Vertical profiles of cesium and lead concentrations in combination with recent eyewitness accounts indicated that these sand layers are correlated with the 1973 Nemuro-oki, 1960 Chilean, and 1952 Tokachi-oki tsunami events. The deeper part of the sediment cores includes three volcanic ash layers and three prehistoric coarse sand layers. The prehistoric layers are correlated with unusually large tsunamis that were geologically identified in previous studies from eastern Hokkaido. These findings suggest that nondestructive techniques, in combination with radionuclide analysis, allow for detection of frequent but faint tsunami deposits. This technique allows for an improved understanding of the history of tsunami inundation in Lake Tokotan and of other locations for which stratigraphic evidence for faint tsunamis layers is not readily apparent from field assessments.

     

Exploring the impact of epistemic uncertainty on a regional probabilistic seismic risk assessment model

Natural Hazards - Probabilistic earthquake loss models are widely used in the (re)insurance industry to assess the seismic risk of portfolios of assets and to inform pricing mechanisms for...     

The barnacle Balanus amphitrite as a bioindicator for Cd: Development and application of a simulation model

The efficacy of the barnacle Balanus amphitrite as a bioindicator for Cd in the environment was investigated through simulation exercises in an ecotoxicological simulation model based on field data. The study showed in general that B. amphitrite is a good bioindicator to record mean trends of the Cd bioavailability in the environment. The model correct reflected differences between high and low patterns of Cd concentrations in the barnacle in the field, but it did not accurately reflect short-term temporal variations. A model investigation pointed out three issues that must be taken into account when using B. amphitrite as bioindicator for Cd bioavailability in the environment: (1) variations in the mean weight of the sampled population may affect the barnacle's Cd concentration determination, specially if a size effect for the metal concentration in the organism is not detected; (2) a sampling effort approximately 5 times greater than that of usually applied in such studies would be required to detect an environmental change that caused a realistic increase in the main source of Cd to the barnacle; and (3) barnacle tissue better responds to long-term changes in the Cd level of its sources.     

Cenozoic thick-skinned deformation and topography evolution of the Spanish Central System

The Spanish Central System is a Cenozoic pop-up with an E–W to NE–SW orientation that affects all the crust (thick-skinned tectonics). It shows antiform geometry in the upper crust with thickening in the lower crust. Together with the Iberian Chain it constitutes the most prominent mountainous structure of the Pyrenean foreland.The evolutionary patterns concerning the paleotopography of the interior of the Peninsula can be established by an analysis of the following data: gravimetric, topographical, macro and micro tectonic, sedimentological (infilling of the sedimentary basins of the relative foreland), P–T–t path from apatite fission tracks, paleoseismic and instrumental seismicity.Deformation is clearly asymmetric in the Central System as evidenced by the existence of an unique, large (crustal-scale) thrust at its southern border, while in the northern one there is a normal sequence of north verging thrusts, towards the Duero Basin, whose activity ended during the Lower Miocene. This deformation was accomplished under triaxial compression, Oligocene–Lower Miocene in age, marked by NW–SE to NNW–SSE shortening. Locally orientations of paleostresses deviate from that of the regional tensor, following a period of relative tectonic quiescence. During the Upper Miocene–Pliocene, a reactivation of constrictive stress occurred and some structures underwent rejuvenation as a consequence of the action of tectonic stresses similar to those of today (uniaxial extension to strike–slip with NW–SE shortening direction). However, the westernmost areas show continuous activity throughout the whole of the Tertiary, with no apparent pulses. At the present time there is a moderate seismic activity in the Central System related to faults that were active during the Cenozoic, with the same kinematic characteristics.     

Planktonic foraminiferal distribution record productivity cycles: evidence from the Aptian-Albian Piobbico core (central Italy)

The Aptian-Albian 'Scisti a Fucoidi' varicoloured pelagic sediments in central Italy, show a 'couplet' alternation of carbonate-rich/carbonate-poor layers, which are interpreted as the sedimentary expression of precession (frequency 19–23 kyr). Carbonate content, chromatic variation, and planktonic foraminiferal abundance were analysed at a 1-cm spacing for a 10-m interval of the Piobbico core, specifically drilled through this formation. Spectral analysis of these parameters shows a prominent signal equated to the c . 100 kyr cycle of orbital eccentricity at a sedimentation rate of 5 mm kyr⁻¹. The coherency of the spectral response of each parameter suggests that a single mechanism controlled the whole sedimentary record. Detailed study of planktonic foraminiferal distribution of the same section at 1-mm scale resolves the Milankovitch frequencies of 41 kyr and 18 to 23 kyr, equated with the obliquity and precessional cycles. But foraminiferal abundance is not in phase with carbonate content, which was largely controlled by calcareous nannofossils, but peaked at intermediate carbonate values. The proposed model for explaining the discrepancy at the precessional level is that foraminifera thrived at intermediate values of the precession index, when the environment was only moderately fertile but stable, while during highs of the precession index, mixing of the water column increased fertility and caused calcareous nannofossil blooms and restriction of planktonic foraminifera to few and tolerant species. The resulting bimodality of foraminiferal abundance per precessional cycle appears to be recorded in the spectrum by peaks at the 11 and 14 kyr levels. Cross correlation of foraminiferal abundances with the calcium carbonate curve over 1–2 Myr intervals produces discrepant results (apparent phase lags) which we attribute to differences in the response to the fundamental eccentricity cycles.