Land-Surface Quantitative Analysis to Investigate the Spatial Distribution of Gravitational Landforms along Rocky Coasts

The increasing availability of high-quality digital elevation models (DEMs) has been associated with a growing interest in developing quantitative analyses aimed at taking advantage of these detailed, updated, and promising digital datasets. Land-surface quantitative (LSQ) analysis is valuable for describing the land-surface topography and performing measures of the signature of specific geomorphic processes, taking into account site-specific geological contexts and morphoclimatic settings, proving to be particularly effective in transitional environments, such as rocky coasts. This paper presents the results of research aimed at investigating the spatial distribution of gravitational landforms along rocky coasts, by means of LSQ analysis based on a DEM with a ground resolution of 2 m, derived from airborne LiDAR (light detection and ranging) surveys. The study area is at Mt. San Bartolo (Northern Marche, Italy) and characterized by a sea cliff diffusely affected by gravitational phenomena of different sizes and types. Geomorphological and geological field data, interpretations of remotely sensed datasets derived from ad hoc unmanned aerial vehicle (UAV) flights, and DEM-derived hillshades were also adapted to support LSQ analysis. In detail, four morphometric variables (slope, roughness, terrain ruggedness index, and elevation standard deviation) were computed and the outputs evaluated based on visual–spatial inspections of derived raster datasets, descriptive statistics, and joint comparison. Results reveal the best performing variables and how combined interpretations can support the identification and mapping of zones characterized by varying spatial distribution of gravitational landforms of different types. The findings achieved along the Mt. San Bartolo rocky coast confirm that an approach based on land-surface quantitative analysis can act as a proxy to efficiently investigate gravitational slope processes in coastal areas, especially those that are difficult to reach with traditional field surveys.

A second-hand shipwreck market: Salvage auctions in mid-eighteenth-century Helsinki

When a merchant ship was wrecked in the Gulf of Finland in the eighteenth century it was salvaged (mainly its running rigging), together with its cargo. In eighteenth-century Sweden, salvage was the monopoly of the Northern Diving and Salvage Company (1729–1802). In Helsinki, several salvage auctions were held each year. Salvage documents are useful sources not only for investigating the demand for ship parts, but also for identifying ships and explaining past marine accidents. The detailed technical knowledge provided by auction protocols offers insight into ships and their equipment in the early modern Baltic. Many ships were on their way to St Petersburg (established in 1703), the home port of European naval stores, but many of them were wrecked on the rocky coasts of Helsinki. This gave rise to a strange kind of shipping based on random imports and the use of recycled cordage, sails and anchors from the shores blessed by unfortunate ships.

Interplay Between Coastal Elevation and Wave Height Controls the Occurrence of Coastal Boulder Deposits in the Aran Islands, Ireland

Coastal boulder deposits (CBD) are wave-emplaced supratidal accumulations that record extreme inundation on rocky coasts. They are poorly understood but are of growing importance as we seek to better understand the extremes of wave power on coastlines. The Aran Islands, Ireland, host CBD in varying settings ranging from sheer cliff tops to wide shore platforms, and at elevations to about 40 m above sea level. Deposits are known to be active during strong storm events and provide a unique opportunity to examine relationships between wave energy, setting, and CBD occurrence. We use topographic elevation (Z) and offshore 100-years significant wave height (Hs,100) to calculate a dimensionless elevation Z* = Z/Hs,100 at 25 m intervals all along the Atlantic-facing coasts of the Aran Islands, and record whether CBD were present or absent at each location. The data reveal universal CBD presence at locations with low dimensionless elevations and near-monotonic decreasing frequency of CBD occurrence as Z* increases. On the Aran Islands, CBD are restricted to locations with Z*<3.13. For high elevation deposits it appears that unresolved local factors may be the major determinants in whether CBD will form. This approach can be applied at any CBD-bearing coastline and has the potential to change the way that we think about these deposits. Evaluation of dimensionless elevations at CBD locations around the world will help build broader understanding of the impact local shoreline conditions have on CBD formation. Determining these relationships contributes to the ongoing need to better understand interactions between extreme waves and rocky coasts.

The Use of UAVs for the Characterization and Analysis of Rocky Coasts

Rocky coasts represent three quarters of all coastlines worldwide. These areas are part of ecosystems of great ecological value, but their steep configuration and their elevation make field surveys difficult. This fact, together with their lower variation rates, explains the lower numbers of publications about cliffs and rocky coasts in general compared with those about beach-dune systems. The introduction of UAVs in research, has enormously expanded the possibilities for the study of rocky coasts. Their relative low costs allow for the generation of information with a high level of detail. This information, combined with GIS tools, enables coastal analysis based on Digital Models and high spatial resolution images. This investigation summarizes the main results obtained with the help of UAVs between 2012 and the present day in rocky coastline sections in the northwest of the Iberian Peninsula. These investigations have particularly focused on monitoring the dynamics of boulder beaches, cliffs, and shore platforms, as well as the structure and function of ecosystems. This work demonstrates the importance of unmanned aerial vehicles (UAVs) for coastal studies and their usefulness for improving coastal management. The Galician case was used to explain their importance and the advances in the UAVs’ techniques.

The interplay between climate, sea-levels and erosion carved in Baltic rauks - complicated love story from Gotland

<p>Gotland and its sister island Faro are one of the hidden gems of Baltic Sea rocky coastal landscapes. The most intriguing, both in terms of morphology and evolution, landforms found along local coasts are rauks or raukars. Those limestone (remnants of Silurian reefs) stacks and pinnacles not only tower above present-day rocky shore platforms and beaches but also appear across numerous uplifted marine terraces and inland slopes. Rauks in often occur in groups or fields called raukfält. Surprisingly, those peculiar landforms have been to some extent neglected by geomorphologists and awaited in-depth study of their micro-relief and potential of the well-preserved marine notches to reconstruct past sea-level and environmental conditions operating on rocky coasts over the Holocene. It is important to note that marine notches are commonly treated as one of the best sea-level indicators, as they form close to the local tidal range.</p><p>In our paper, we present the results of the most recent mapping of raukars fields in key localities in northern Gotland and Faro including Langhammars, Digerhuvud, Gamla Hamn, Lergrav and Asundens. We measured the shape and elevation of marine notches above present-sea level using Terrestrial Laser Scanning and characterized the degree of weathering of rock surface of raukars bases and well-preserved notches using Schmidt hammer rock tests. In addition to morphometric and geotechnical tests, we monitored modern rates of downwearing of shore platform constitution base of rauks and tops of the local cliffs and rocky escarpments. We discuss the results of selected field surveys with well-established climatic reconstructions and the recently constructed Holocene shore displacement curves of Gotland. We hypothesize that the shape of detected notches not only indicate positions of former sea-levels but also could give us an insight into the differences in the efficiency of erosional and weathering processes operating on rauk surface (notch formation) during periods of different salinity and water temperature, characteristic for Holocene evolution of Baltic Sea.</p><p>This is the contribution to the National Science Centre in Poland project ‘RAUK- forgotten witness of Holocene sea-level changes and development of Baltic rocky coasts’ (UMO-2016/21/D/ST10/01976).</p>

Volumetric Change Detection in Bedrock Coastal Cliffs Using Terrestrial Laser Scanning and UAS-Based SfM

Three-dimensional (3D) morphological changes in rocky coasts need to be precisely measured for protecting coastal areas and evaluating the associated sediment dynamics, although volumetric measurements of bedrock erosion in rocky coasts have been limited due to the lack of appropriate measurement methods. Here we carried out repeat surveys of the 3D measurements of a small coastal island using terrestrial laser scanning (TLS) and structure-from-motion (SfM) photogrammetry with an unmanned aerial system (UAS) for 5 years. The UAS-SfM approach measures the entire shape of the island, whereas the TLS measurement enables to obtain more accurate morphological data at a scale of centimeters on the land side. The multitemporal TLS-derived data were first aligned in timeline by the iterative closest point (ICP) method and they were used as positionally correct references. The UAS-SfM data were then aligned to each of the TLS-derived data by ICP to improve its positional accuracy. The changed areas for each period was then extracted from the aligned UAS-derived point clouds and were converted to 3D mesh polygons, enabling a differential volume estimate (DVE). The DVE for each period was revealed to be from 3.1 to 77.2 m3/month. These changes are rapid enough to force the coastal bedrock island to disappear in 30 years. The temporal variations in the DVE is roughly associated with those in the frequency of high tidal waves.