Ramsey Island Research Articles

Development of a Tool to Optimise Tidal Stream Energy Sites

Several prospective tidal energy sites have been identified around the UK, however, little is known about the specific, and often complicated, hydrodynamics in many of these area [1]. Many sites comprise complicated seabed and coastline configurations, which can not only give rise to fast-flowing currents, but also results in highly turbulent and spatially-varying currents. These latter features are undesirable characteristics for devices.
 Tidal stream energy developers seldom design devices to suit a particular site, rather devices are designed and suitable sites located subsequently. This reduces the number of viable sites as each device has its own design constraints, e.g. minimum water depth, minimum velocity, etc. In order to maximise the exploitability of these sites, where space is generally limited, it would be more beneficial for developers to design devices once site conditions/constraints are better understood.
 An open-source tool is being developed that determines the physical constraints of a site based primarily on bathymetry and current velocities (measured and/or modelled). This tool aims to optimise a site to help developers understand what conditions need to be met in order to maximise energy generation – it will also identify which areas are unsuitable depending on the device design. The flexibility of the tool ensures two key aspects:
 
 For existing devices, the device design parameters can be selected to show which areas are viable that meet these parameters (e.g. maximum bed slope, maximum current velocity, etc.);
 For devices yet to be designed, different design parameters can be selected to optimise a site to help maximise the energy that can be extracted from a particular site.
 
 
 The tool is being written in Python with a QGIS front end to allow the user to make changes readily and choose which parameters are important. Not only will the tool identify suitable sites based on user-defined parameters, it will also calculate how much power is available (in kW/m2) based on velocity data.
 Given the data availability and interest from tidal energy developers in Ramsey Sound (Figure 1) and to the west of Ramsey Island in West Wales, UK, this site has been chosen as a case study. This site also experiences significant spatial and temporal variation in flow, caused in part by a narrowing of the Sound, which accelerates flow [2]. Once this tool has been proven it will be expanded to assess the viability of other tidal energy sites, both in the UK and overseas. Sensitivity testing is currently underway to determine how sensitive the tool is to data resolution. For example, do higher resolution bathymetry and velocity datasets provide a marked difference in the areas that are viable. 
 This tool will demonstrate that developers (and other relevant parties in the supply chain) cannot rely on first-order appraisals, which may make energetic tidal straits attractive sites for development since their resource potential depends on flow conditions that are fundamentally local.

Grey seal (Halichoerus grypus) disturbance, ecotourism and the Pembrokeshire Marine Code around Ramsey Island

The world wide growth of ecotourism and the need for management of this growth is well documented. Ramsey Island in Pembrokeshire, UK, is examined here in the context of its population of Atlantic Grey Seals. The growth of ecotour boat activity around the island has lead to the development of a voluntary code of conduct for relevant stakeholders, defining limits to their behaviour around key species at the site, including grey seals. Semi-quantitative protocols were developed for recording disturbance and boat behaviour. Data are presented of seal disturbance behaviour at pupping beaches in response to numbers, distance and speed of boats. It is shown that there is a significant correlation between the intensity of disturbance as measured by a disturbing stimulus index (DSI) and disturbance level. Disturbance is measurable at levels of disturbing stimulus that currently would not breach the code recommendations. The findings are examined for their implications for the seal populations, compliance with the code of conduct and wider definitions of ecotourism. Recommendations for adjustment of the code in terms of boat distance and speed are made. We highlight the need for wider stakeholder discussion of whether such common pool resources can be sustainably managed by voluntary measures alone.

Ordovician bimodal volcanism in SW Wales: geochemical evidence for petrogenesis of the silicic rocks

Rhyolitic lavas, pyroclastic, and high-level intrusive rocks form an important component of a bimodal tholeiitic basalt-rhyolite association of early Ordovician (Llanvirn) age exposed in North Pembrokeshire, on Ramsey Island, in the Fishguard area, and on Mynydd Preseli. In the same region, a 400 m thick tholeiitic layered differentiated sill, the St David's Head intrusion, considered to be co-genetic with this association, comprises a series of units ranging from basic (olivine + orthopyroxene-bearing gabbros) through intermediate (granophyric gabbro) to acidic (aplite) compositions. Consideration of the major and trace element concentrations in these various intrusive units suggests that they are related largely through a crystal fractionation process. The principal fractionating phases were clinopyroxene and plagioclase feldspar, with olivine and orthopyroxene in the more mafic compositions, substantial Fe-Ti oxide and minor apatite in the intermediate compositions, and minor apatite and titanite in the most evolved compositions. A comparison between the composition of a typical aplite from the St David's Head intrusion and compositions of the various silicic rocks from the bimodal suites in North Pembrokeshire suggests these latter rocks have also been derived from a more basic tholeiitic magma via crystal fractionation. Potential parental magmas are the various basaltic lavas and related doleritic intrusions of the Fishguard Volcanic Complex. However, certain silicic lavas and intrusions from the Porth Maen Melyn area appear not to have been derived from a tholeiitic parental magma, but rather have a calc-alkaline type chemistry, similar to older lavas of the Trefgarn Volcanic Group exposed a short distance to the south of Fishguard. These findings support the contention that large volume silicic units in bimodal associations can be derived by crystal fractionation, despite the obvious geochemical discontinuity, and the apparently anomalous volume relationships commonly present.

Submarine silicic volcanism and associated sedimentary and tectonic processes, Ramsey Island, SW Wales

Lower Ordovician marine strata, formed in an ensialic marginal basin environment, record early episodes of distant explosive silicic volcanism and a later volcanotectonic episode which was a precursor to the development of a wide variety of near-to-source submarine silicic volcanic phenomena. The early episodes are represented by well-bedded turbiditic tuffs. These and older strata, at least 770 m thick in normal stratigraphical succession, are allochthonous, and large-scale wet-sediment sliding with reworking of strata in cohesive debris flows reflects major disturbance of the sea floor during the emplacement of silicic magmas. Volcanotectonic uplift along a N-S fault exceeded 1 km and led to the emergence and erosion of a rhyolitic volcanic island. This was followed closely by submergence, and in water depths perhaps of about 500 m there accumulated welded and non-welded rhyolitic ash-flow tuffs, rhyolitic turbiditic tuffs, rhyolite lavas and a wide variety of debris flow deposits. Shallow intrusions of 'low'-viscosity rhyolite were emplaced contemporaneously. The more or less simultaneous emplacement of rhyolitic tuff with both 'low'-viscosity and high-viscosity rhyolites is attributed to variable water content related perhaps to volatile fluxing in a magma body. The location of the near-to-source extrusive rocks and consanguineous intrusions along the contemporary N-S fault is considered to reflect channelling of magma, initially along a deep crustal fracture.

Fluidization of wet sediments during the emplacement and cooling of various igneous bodies

During the emplacement and cooling of igneous bodies, fluidization of wet sediment by water vapour may occur by heating, or by pressure relief during the opening of fractures. Momentary fluidization causes sediment reconstitution and local transport. Continuous fluidization can result in substantial sediment displacement. Theoretical considerations show that fluidization due to heating is not likely to occur at depths where pressure is much greater than 312 bars. Studies of the emplacement of sills of andesite (Ayrshire), fluid rhyolite (Ramsey Island) and viscous rhyolite (Moelwyn Hills) recognize a wide range of phenomena attributable to wet sediment fluidization and in places modify existing interpretations. The transgressive bases of the subaqueously welded ash-flow tuffs of the Capel Curig Volcanic Formation are consistent with emplacement attended by fluidization of the subjacent sediment. Evidently fluidization is a means by which large volumes of wet sediment can be replaced by igneous material with minimal disturbance of the remaining host. Also, fluidization can result in exceptionally complex contact relationships between sedimentary host and intrusive rocks, and can cause fractures formed during cooling to be thoroughly pervaded by sediment. Fluidization is commonly associated with the formation of peperites.

The Spatial Distribution of Ants' Nests on Ramsey Island, South Wales

(1) Ramsey Island (260 ha), Dyfed, Wales was surveyed by random quadrat sampling for ants' nests, and twelve variables of the habitat associated with each nest. (2) Nine species of ants from four genera were found. The average nest density was 0.057 m-2, with a maximum of 0 61 m-2. The distributions of the five commonest species are analysed in detail. (3) Nest dispersion is highly contagious (conforming to a logarithmic model), resulting from high nest densities in a few favourable sites. There is incomplete segregation of each species in the habitat, indicated by a random distribution of species packing. (4) Three physical and nine vegetational variables of the habitat are considered singly and in combination as niche dimensions. The variables are compared in a correlation matrix, and three principal components extracted. (5) The first component, representing an exposure factor differentiates the exposed coastal habitat of Lasius alienus F6rster from the sheltered sites of L. niger L. in heath and grassland vegetation. The second representing a drainage factor separates these two species from Myrmica scabrinodis Nylander and M. sabuleti Meinert. The third represents altitude and differentiates Lasius flavus F. from the other Lasius species, as well as Myrmica sabuleti from M. scabrinodis. (6) The nest dispersions of all Ramsey's ants are compared, and explained by specific and generic differences in nest building and foraging behaviour. The canopy effect of vegetation and the importance of rabbit grazing are discussed. (7) It is concluded that the dispersion and density of nests are broadly determined by the pattern of habitats on Ramsey and the factors influencing them, particularly exposure, moisture and rabbit grazing. The most widely distributed ants are generalist in their physical and vegetational resource requirements and can built a variety of nest structures. Lasius flavus typifies this group as it is able to nest at high and low densities in a range of habitats, either as the dominant species or in co-existence with as many as four other species.

Early Ordovician volcanism in Dyfed, SW Wales

Summary A review of early Ordovician volcanism in SW Dyfed, Wales is presented in the light of recent work. There were a number of major and minor volcanic episodes within the area during Arenig and Llanvirn times. For the most part, submarine volcanism occurred within a restricted basin, in which black muds were deposited and to which coarse terrigenous material had very limited access. Basic and intermediate magmas were generally erupted as flows. Acidic magmas were also erupted quietly, to produce thick, frequently autobrecciated flows and domes. Volcaniclastic rocks resulted by deposition from sediment gravity flows originating on unstable flanks of lava domes. Evidence for occasional episodes of explosive activity is provided by sediment gravity flows carrying a high proportion of pyroclastic debris. Subaerial or shallow water conditions are suggested only for the oldest volcanic rocks on Ramsey Island. Numerous basic and less frequent intermediate and acid high-level intrusive sheets have a close temporal, spatial and genetic relationship with the volcanic rocks.

The grey seal ( Halichoerus grypus) in Cornwall and the Isles of Scilly

Cornwall and the Isles of Scilly were explored for grey seal ( Halichoerus grypus) breeding localities during the 1973 breeding season. The work invelved investigating many sea caves on the north coast of Cornwall, in addition to open beach and skerry sites. Pup production was determined by relating the number of pups produced in a sample period to the number produced in the same period (in another year) at Ramsey Island, Pembrokeshire. The all-age populations derived from these pup production estimates suggest that the number of grey seals in Cornish waters is about 250 and in Scilly about 120. Haulouts of several hundred animals seen in Scilly outside the breeding season almost certainly breed elsewhere.

Observations on the Grey Seal (Halichoerus grypus) at Ramsey Island, Pembrokeshire.

Summary.A brdding colony of the grey seal was studied in the autumn of 1947 at Ramsey Island. The arrival of both sexes at the breeding grounds is discussed and also their behaviour prior to the birth of the calves. The history of the calf while on the beach is summarized, and calving rate, sex ratio and infant mortality are discussed. The movements of the immature and non‐breeding population are dealt with, and a description is given of the fur colour and age and sex distinctions. An attempt is made to elucidate population dynamics and the status of the species in South Wales. It is postulated that the Ramsey seals are traditionally cave‐breeders and that open beach breeding is a recent habit. Finally a comparison is made between the development and behaviour of Ramsey seals and those of Scottish colonies. It is shown that at Ramsey the adults are less dependent on land and the young are generally more precocious.

Note on the geology of Ramsey Island

Note on the geology of Ramsey Island

Descriptions of the Graptolites of the Arenig and Llandeilo Rocks of St. David's

I n the neighbourhood of St. David's, the Arenig rocks, described by Mr. Hicks in his paper read at the last meeting of the Geological Society*, are the earliest in which Graptolites are known to occur; and yet, when once they appear, so diversified are their forms that these Pembrokeshire rocks are only equalled, in the number and variety of the genera they contain, by the Canadian Graptolite-bearing rocks of equivalent age known as the Quebec Group. In more ancient deposits two species only, belonging to one of the two great sections into which these fossils are divided, have hitherto been detected, viz. Dictyograptus (Dictyonema) socialis , Salter, and Dendrograptus Hallianus , Prout. The former occurring in the lower portion of the Tremadoc rocks of North Wales, and the latter in the equivalent strata (the Potsdam Sandstone of America), it is impossible to say which genus is the earlier, or whether the group is first represented in Britain or in America. Before the discovery, in 1872, of the extensive series of Graptolites which characterize the Lower Arenig rocks of Ramsey Island, the Skiddaw Slates of Cumberland were supposed to be our earliest Graptolite-bearing rocks; but it is now known that the lowest rocks of the Arenig Group exposed in the vicinity of St. David's, in which Graptolites abound, are of greater age than any part of the Skiddaw Slates yet described; and it is highly probable that they are also older even than the lowest beds of the Quebec Group known to contain

On the Cambrian and Silurian Rocks of Ramsey Island, St. David's

On the Cambrian and Silurian Rocks of Ramsey Island, St. David's

On the Tremadoc Rocks in the neighbourhood of St. David's, South Wales, and their Fossil Contents

The occurrence near St. David's, in South Wales, of rocks supposed to be of the age of the Tremadoc Slates of North Wales, was mentioned in a Report by the late Mr. Salter and myself to the British Association in 1866; and a list of the fossils which had up to that time been discovered in them was also given. Several new forms, however, have since been found in these rocks, and some of them very recently, during researches made at Ramsey Island by Messrs. Homfray, Lightbody, Hopkinson, and Kirshaw, in conjunction with myself. The Brachiopoda were figured by Mr. Davidson in his paper “On the Earliest British Brachiopoda,” in the Geological Magazine for July 1868; and a supposed land-plant was named by me Eophyton explanatum in the same publication for Dec. 1869; but with the exception of these, the whole of the fossils, comprising a rich and exceedingly interesting fauna, are as yet undescribed. In the present paper I propose to describe all these new forms, and also to give some account of the lithological characters of the strata in which they occur, their relation to the other formations, and their geographical distribution in the neighbourhood of St. David's. On the map (fig.1) it will be seen that there are three distinct patches of these rocks shown, viz.:—at Ramsey Island, on the eastern coast; at the north end of Whitesand Bay, and extending for some distance in a N.E. direction; and in a district about five miles east of

Geology: Structure of Eophyton

THE Geological Magazine for the present month contains a paper by Mr. Henry Hicks, describing the structure of a fossil, from the Lower Arenig rocks of Ramsey Island, near St. David's, which he considers to be an Eophyton, resembling E. Linnœanum of Torell. The rocks in which this fossil occurs rest conformably upon Upper Lingula flags, and underlie rocks of the Skiddaw or Tremadoc series.

II.—Notes on a Species of Eophyton (?) from the Lower Arenig Rocks of St. David's

As none of the figures hitherto given of the genus Eophyton show either its internal structure, or articulations of its stems, and as I am in possession of a specimen from the Lower Arenig Rocks, of Ramsey Island, near St. David's, which resembles in some respects the Eophyton Linnœanum Torell, but which shows both articulations of the stem, and an internal vascular structure, a description of the species may probably be useful, and may tend to elucidate the true nature of Eophyton, concerning which so much doubt seems to exist at present.