Rock Shelf Research Articles

A Nonaxial-Type Swirling Cavitating Nozzle for Exploiting Natural Gas Hydrate

Summary Natural gas hydrates (NGHs) have garnered widespread attention in the new energy sector, owing to their efficient and clean combustion properties. NGHs are ice-like substances formed by methane and water under high-pressure and low-temperature conditions, abundantly deposited in seabeds and frozen soil of highlands on Earth. However, the rock shelves of NGH reservoirs are mostly fragile and sparsely colloidal. Traditional mechanical mining methods can easily cause rock-shelf collapses, leading to mining accidents. Long-term indoor experiments and pilot mining projects have shown that cavitating nozzles can provide a feasible solution to the problem of efficient mining of NGHs. To further improve the efficiency of cavitating nozzle mining for NGHs, we have optimized and designed a nonaxial-type swirling cavitating nozzle (NASCN) based on traditional swirling cavitating nozzles (SCNs). Both numerical simulations and indoor experiments have verified the higher mining performance of this nozzle. In the numerical simulation experiments, we analyzed the cavitation performance, erosion performance, and energy consumption characteristics of different cavitating nozzles using the mixture multiphase flow model and the renormalization group (RNG) k-ε turbulence model. In the indoor experiments, we utilized a jet erosion experimental device for NGHs to analyze the erosion effects of different cavitating nozzles on hydrate samples. The results of these experiments indicate that the NASCN reduces energy consumption by 12% compared with traditional nozzles when there is little difference in cavitation performance and erosion performance. Moreover, under similar energy consumption, the NASCN improves erosion efficiency by 35.2% compared with traditional nozzles. These results demonstrate that the NASCN has good application value in the mining engineering of NGHs.

Malacofauna of Bolków castle (Lower Silesia, SW Poland) – trends and perspectives

Bolków castle is located in the Lower Silesian voivodeship near the Kaczawskie Mountains. Malacological studies were carried out in 2006, 2010 and 2021. In 2006, specimens were collected only by hand, but in 2010 and 2021 samples were also made by litter sieving and from material taken from rock shelves and walls. Overall, 35 species were found, but the numbers declined over time: 28 species in 2006, 26 in 2010 and 20 in 2021. Two species recorded before our studies were not found again. Abundance declined greatly between 2010 and 2021. Over this period, open-country species declined the most, and shade-loving species increased as a proportion of the whole. In particular, the open-country Pupilla muscorum, eudominant in 2010, was absent in 2021, while the tolerant Alinda biplicata increased greatly over the same period. While more widespread environmental or climatic change may be involved, the castle has been subject to increased human pressure and a renovation programme in 2015. Castle faunas, here and elsewhere, are not only refugia for locally or nationally uncommon species, but provide a basis for regular monitoring of faunal change. Other castles in the region, most especially those at Stary Książ and Książ have similar faunas, and can be used in the same way.

Environmental Factors in Spawning of Wild Devils Hole Pupfish Cyprinodon diabolis (Teleostei: Cyprinodontidae)

The sole wild population of the endangered Devils Hole Pupfish, Cyprinodon diabolis, has declined to fewer than 40 individuals twice since 2006, prompting increased recovery efforts. The U.S. Fish and Wildlife Service's Devils Hole Pupfish recovery plan stipulates two reproducing captive populations, though, historically, propagation efforts have yielded little success. To address information deficits in reproductive behavior and ecology, from February–December 2010 we investigated environmental factors associated with spawning activity of C. diabolis in Devils Hole, Nevada, USA. An underwater camera continuously monitored a portion of a shallow, submerged rock shelf used for spawning. Select biotic, abiotic, and physico-chemical parameters were monitored continuously throughout the year. Water level and precipitation data provided by the U.S. National Park Service identified disturbances from earthquake-induced seiches and storm-induced flash floods. Zero-inflated Poisson regression provided a model with 28% predictive power with algal cover, light energy, and seiches as the three strongest predictors among tested factors in spawning behavior of C. diabolis in the wild.

Forest Stands in Phyllitido-Aceretum Community Occurring on Limestone Rocks and Shelves – Comparison of their Structure in Strictly Protected and Managed Forests

The aim of the study was to determine the structure of forest stands in rare Phyllitido-Aceretum communities, which grow in extremely harsh conditions – steep limestone slopes and rock shelves. Permanent research plots were established in five well-developed patches of Phyllitido-Aceretum communities from Krakow-Czestochowa Upland (Poland). Two of the plots were located in strictly protected areas of the Ojcow National Park, whereas another three were established in the managed forests of Olkusz Forest District. The species composition of the forest stands was determined, including all dead and live trees and their diameters at breast height were measured. Moreover, the horizontal coordinates of each tree were measured to determine the spatial pattern of the trees. Ripley's L function was used for the spatial pattern analysis.The research showed that the patches of Phyllitido-Aceretum communities are characterized by rich species composition of tree layers; nine species were found. There was no significant difference in the species composition between the living and dead trees and the shares of particular species were similar. The density and share of live trees in the phytocoenoses located within the strict protection zone were significantly lower than in managed forests. On the contrary, the same parameters when calculated for dead trees were significantly higher in phytocoenoses located in protected zones than in managed forests. The spatial distribution of the trees in all the analysed plots (except one) displayed a clumped pattern, which is observed in various spatial scales and reflects the habitat mosaics and life strategies of species typical for Phyllitido-Aceretum community.

A novel support system for shallow buried caverns based on the mining method

In order to maintain the original appearance of the rocks on a cavern roof and protect the ground environment, a new supporting method for shallow-buried caverns is proposed. This study investigates the design theory and construction process. Based to this method, some crisscross small tunnel sheds are embedded in the overburden layer. Hence a supporting system of interaction between surrounding rocks and supporting structures is formed. By combining the numerical calculation with monitoring measurement, we found that the distribution of calculated deformation generally agreed with the monitoring measurements. The monitoring results revealed that the proportion of rock shelf load-bearing reached 47%. The self-bearing capacity of the surrounding rocks is brought into significantly play.

Underwater Videography Outperforms Above‐Water Videography and In‐Person Surveys for Monitoring the Spawning of Devils Hole Pupfish

AbstractThe monitoring of threatened and endangered fishes in remote environments continues to challenge fisheries biologists. The endangered Devils Hole Pupfish Cyprinodon diabolis, which is confined to a single warm spring in Death Valley National Park, California–Nevada, has recently experienced record declines, spurring renewed conservation and recovery efforts. In February–December 2010, we investigated the timing and frequency of spawning in the species' native habitat by using three survey methods: underwater videography, above‐water videography, and in‐person surveys. Videography methods incorporated fixed‐position, solar‐powered cameras to record continuous footage of a shallow rock shelf that Devils Hole Pupfish use for spawning. In‐person surveys were conducted from a platform placed above the water's surface. The underwater camera recorded more overall spawning throughout the year (mean ± SE = 0.35 ± 0.06 events/sample) than the above‐water camera (0.11 ± 0.03 events/sample). Underwater videography also recorded more peak‐season spawning (March: 0.83 ± 0.18 events/sample; April: 2.39 ± 0.47 events/sample) than above‐water videography (March: 0.21 ± 0.10 events/sample; April: 0.9 ± 0.32 events/sample). Although the overall number of spawning events per sample did not differ significantly between underwater videography and in‐person surveys, underwater videography provided a larger data set with much less variability than data from in‐person surveys. Fixed videography was more cost efficient than in‐person surveys ($1.31 versus $605 per collected data‐hour), and underwater videography provided more usable data than above‐water videography. Furthermore, video data collection was possible even under adverse conditions, such as the extreme temperatures of the region, and could be maintained successfully with few study site visits. Our results suggest that self‐contained underwater cameras can be efficient tools for monitoring remote and sensitive aquatic ecosystems.Received April 17, 2015; accepted September 10, 2015

Spatial aspects as seen from a density analysis of lithics at Middle Pleistocene Qesem Cave: Preliminary results and observations

This paper focuses on the results of a preliminary study of flint items densities in different areas and different parts of the stratigrapahic column of Qesem Cave. Qesem Cave is a karst chamber cave with a ∼10 m stratigraphic sequence assigned to the Acheulo-Yabrudian Cultural Complex (AYCC) of the late Lower Paleolithic in the Levant dated to 420–200 ka.We first show the range of lithic densities in studied assemblages in the cave emphasizing significant differences in both the total number of lithic items per volume unit and/or for selected artifact categories within these assemblages. The results are used to suggest differential intensity of lithic-related activities in the cave and variability in synchronic (different areas of the cave within a similar stratigraphic level) distribution aspects of lithic categories of selected assemblages. We briefly note on the diachronic (assemblages belonging to different parts of the stratigraphic sequence) aspect of lithic densities in the discussion, yet this aspect is not is not central in this paper.A comparison of densities to frequency compositions of selected techno-typological categories in the same assemblages/areas further emphasizes the importance of using more than one quantitative measure as a descriptor of lithic assemblages and the interpretative potential of the interplay between the two measures. In some analyzed aspects the differences between the two measures in the same assemblage are quite significant, enabling interpretation of activity areas and specific human behaviors.Eventually, further research testing lithic densities against and/or incorporating them with other sets of density (and frequency) data from the same areas (e.g., faunal remains), or relating these densities to natural (such as a rock shelf) or human made features (such as a fireplace), may offer an elaborate and valuable landscape for reconstructing human behavior at the cave. Furthermore, the spatial distribution of specific techno-typological lithic categories within the assemblages studied as seen in densities augmented by available functional data (derived from use-wear analysis) enable another perspective on the subdivision of activity areas in some parts of the sequence.One synchronic example of our preliminary results which we present relates to generally contemporaneous assemblages adjacent to a constructed fireplace in the center of the cave in the upper part of the lower stratigraphic sequence dated to ca. 300 ka. Both blade-dominated Amudian and Quina (and demi Quina) scrapers dominated Yabrudian assemblages are involved, indicating spatially differentiated, functionally related differences around the fireplace.

Amudian versus Yabrudian under the rock shelf: A study of two lithic assemblages from Qesem Cave, Israel

This paper presents new results of a lithic study of two distinct lithic assemblages from the Qesem Cave “Shelf” area in the northwestern part of the cave – one Yabrudian and one Amudian, both older than 300ka. The two assemblages exhibit clear stratigraphic relations, the Yabrudian being deposited on top of the Amudian. A detailed techno-typological study of the two assemblages (n = ∼30,000 artifacts) is presented as well as a comparative analysis between them. The results indicate that the Yabrudian and Amudian of the “Shelf” area are part of the same technological system sharing similar techno-typological features. Differences are mainly at the relative frequency level and in the density of the various elements of the assemblages. These results suggest that the differences between the assemblages might be related to differences in human activities in the different strata of the “Shelf” area using different tool-kits and not to differences in technology or any other cultural conception.

Distribution and ecology of Chaenocephalus aceratus (Channichthyidae) around South Georgia and Shag Rocks (Southern Ocean)

Chaenocephalus aceratus (Family Channicthyidae) is one of the dominant species of demersal fish living on the South Georgia shelf where it is caught in low numbers as by-catch in the mackerel icefish and Antarctic krill commercial fisheries. Data collected during 14 demersal fish surveys, from 1986 to 2006, are analysed to investigate biomass, distribution, growth and diet. Biomass estimates from a swept area method ranged from 4,462 to 28,740 tonnes on the South Georgia and Shag Rock shelves although few fish were caught at Shag Rocks. Analysis of length frequency data indicated that growth was fast in the first five years with males and females attaining lengths at first spawning of 440 mm TL and 520 mm TL. The diet was comprised of fish and crustaceans, with an ontogenetic shift in diet from Euphausia superba and mysids to benthic fish and decapods observed to begin at 250 mm TL. In larger fish (>500 mm TL) the diet was dominated by fish. C. aceratus diet is sufficiently different from the other species of channichthyids around South Georgia to suggest that these species have undergone resource partitioning.

Notes on the Rediscovery, Status, and Ecology of the Very Rare Hawaiian Fern Christella boydiae (Thelypteridaceae)

The genus Christella (Thelypteridaceae) is comprised of approximately 50 species distributed predominantly in the Old World tropics but also in the Americas (Holttum 1977). Two native Christella species, C. cyatheoides (Kaulf.) Holttum and C. boydiae (Eaton) Holttum occur in Hawai'i (Wagner, 1981). Christella cyatheoides is a common and characteristic component of matted fern understory of Hawaiian rain forest. Christella boydiae is a much rarer diminutive species of rocky stream courses. Christella boydiae has been collected only from the Ko'olau range of O'ahu, Kipahulu and Waiho'i Valleys on East Maui, and along low elevation watercourses near Hilo on Hawai'i. Currently it is only known from one of these historic populations at Kipahulu Valley. There are 20 specimens of C. boydiae in the Bernice Pauahi Bishop Museum Herbarium Pacificum (BISH) that represent 18 or fewer collections. Most of these specimens are in poor condition and as typical of collections made prior to 1910, have little or no collection information. The species has been most often collected on O'ahu. Of these, six specimens (one third of the total at BISH) were made between 1900 and 1908 by either of the noted Hawaiian botanists, C.N. Forbes or J.F. Rock, mostly from the Punalu'u region of the Ko'olau range. The last collection of Christella boydiae on O'ahu was made prior to 1908. However, Warren H. Wagner found that this species was still present in the Punalu'u area of the Ko'olau range on O'ahu as late as 1965 (Kaluanui Stream, rock shelves, Castle trail, Hau'ula Forest Reserve, Ko'olau range, W H. Wagner and S. Carlquist 65270 MICH). Since that time, many exotic weeds, noteably Clidemia hirta (Melastomataceae), have invaded the area and this species has apparently disappeared. On Hawai'i island, the species, to our knowledge, has been collected only once. Until recently, Christella boydiae had been collected only three times on Maui, first in 1881 in Kipahulu Valley (EL. Clarke s.n., BISH) without further location information. Then after 86 years, C. boydiae was again collected in Kipahulu Valley in 1967 (R. DeWreede 30) along Palikea stream at 915m (Lamoureux, 1968). A third Maui collection was made in 1973 in adjacent Waiho'i Valley as part of the NSF-sponsored Waiho'i Valley Research Project (B. Harrison 10) at 915-1040 m along Waiohonu stream where it was a rare fern from a shady location under a ledge associated with hymenophyllaceous ferns and various mosses along the stream bank (B. Harrison-Gagne, pers. comm.). Neither of these collections is present in the cabinets at the Herbarium Pacificum (BISH): although the latter is in the University of Hawai'i collection. Fourteen specimens at the Herbarium Pacificum (BISH) include the year of collection. Of these, eight were collect86

The Use and Misuse of Charts

We recognize that in the general line of trade (or, as we have had underlined again recently, of war) there will be places where ships have to go but where, with the best will in the world, we have not been able to provide adequate charting or even to recommend anyone else's chart as fit for use. The master and his owners, or the naval commanding officer and his operational authorities, have got to weigh the advantages of calling at that port, or using that route, against the danger to the ship and decide whether the gain justifies the risk.In 1973 we were astonished to hear that a foreign coaster on passage from a Bristol Channel port to Penzance had attempted to go between Godrevy Point, the north-eastern head of St Ives Bay, and Godrevy Island, some 2½ cables offshore, at low water. Fortunately for her, she was spotted by the local coastguard before she was irrevocably committed to the passage – and dissuaded. The largest scale chart of the area, Chart 1168, is on a scale of 1: 25000, and shows the passage as some ¾ inch across from high waterline, or less than half an inch between drying rock shelves. Admittedly it did show a narrow gap where the contour lines suggested that more than 5 m of water could be carried through the centre of the passage. The sailing directions state that the channel outside the island, between it and the outer shoals, should not be used without local knowledge. The inner passage is briefly mentioned but no instructions for passing through it are given.

Dependence of the pressure against a supporting mass on its shrinkage during the excavation of steep rock shelves

Dependence of the pressure against a supporting mass on its shrinkage during the excavation of steep rock shelves

Nearshore fish habitat utilization and species associations in Lake Opinicon (Ontario, Canada)

The bulk of Lake Opinicon fish biomass is concentrated in the physically diverse inshore areas. Quantitative analysis of the community compositions of the various inshore habitat types (weedy inlets, sandy shallows, rock shelf, gravel, etc.) showed that each supported a characteristic assemblage of fishes with a relatively constant species and year class composition. This was maintained throughout the season despite a drop in fish biomass in late summer when there was a progressive movement into the offshore waters.

The Transgression of a Hard Substrate Shelf: The Llandovery (Lower Silurian) of the Welsh Borderland

ABSTRACT Llandovery rocks of the Welsh Borderland document sedimentation on an irregular hard rock shelf during an eastward transgression. Two transgressive phases are recognized. During the first, a southward facing peninsula was flanked to the east (shore-wards) by stream-fed beaches and trapped estuarine sediments; and to the west (seawards) by a tide-swept bank undergoing in situ grading. To the south, westward prograding deltas countered the initial transgression. During the second phase, nearshore tidal and wave activity shifted eastwards· Thickness considerations suggest that offshore, muds were deposited from seawater with a suspended mud content closer to the present waters of the North American East Coast outer shelf than the more muddy North Sea. Storms generated many of the laminated sandstones and coquinas interbedded with the muds. The shelf attained a climax graded condition in late Llandovery times. The main factors controlling sedimentation were topography, tides, waves, fluviatile influx and storms. Many aspects of Llandovery sedimentation are only observed individually in other transgressive sequences.

The origin of the Mersey anD Dee Estuaries

AbstractThe present coastal configurations of these estuaries are contrasted with known fluvial drowned estuaries and attention is drawn to their non‐fluvial characteristics. Two other sub‐parallel depressions in Wirral and southwest Lancashire are described, together with the sub‐glacial surfaces of all four. Their floors are found to contain irregular rock‐bound hollows, and other features reminiscent of glaciated areas. It is suggested that they are escape routes taken by Irish Sea ice hemmed in by the mountains of Wales and the outliers of the Pennines. The term “iceways” is suggested for such ice‐gouged features. A rock shelf in the University area of Liverpool is also tentatively attributed to the same ice erosion.

Part III. A Possible Middle Helladic Fortification Wall

Schliemann on his plan of the acropolis of Mycenae marks a terrace wall on the north-west corner of the ‘summit’. Steffen on his plan of the acropolis marks the same wall as one of his ‘kyklopische Stutz- u. Abschnittsmauern’. Dr. Leicester Holland included the wall in his plan of the palace made during our excavations there in 1920–23. Then we thought that this wall was a terrace wall which supported the end of the inclined roadway which climbed the Citadel from the Ramp to the north-west Propylon (9) of the Palace with its paved forecourt (7).In 1939 in excavating the rock shelf to the east of the Guardroom (3, 4) and below the terrace wall which supports the temple foundations on the north, we found a much ruined wall (Fig. 7, Z) on the very edge of the rock shelf, which here drops abruptly to the north. This wall was associated with a Middle Helladic deposit. Above this lay a somewhat disturbed Late Helladic stratum where the splendid ivory group of two women and a boy was discovered. The wall is a packed construction of largish stones about 1·25 m. thick, and the deposit behind it rests in a hollow in the rock and was at most 1·25 m. deep.

High Terraces and Abandoned Valleys in Western Pennsylvania

The terraces with which this paper has to do are the well-known gravel-covered rock shelves found along the Allegheny, Monongahela, and other large streams of western Pennsylvania, about 200 feet above present stream channels. The abandoned parts of valleys are closely associated with the terraces, being found at the same elevation, and in many places the two are connected. Fig. i shows the principal areas of high terrace. The region includes all the Ohio River basin above New Martinsville, where there was formerly a divide. There are, however, terraces and abandoned parts of valleys of the same age on the Kanawha, Guyandot, Big Sandy, Kentucky, and other streams. The impressiveness of these features is attested by the long list of names of eminent men who have studied and described parts of them. This list includes Stevenson, Leslie, Jilson, Chance, Wright, Chamberlin, Gilbert, I. C. White, Tight, Campbell, E. H. Williams, Leverett, and others. Some of the earliest workers believed that the terraces were due to a submergence and marine erosion. Stevenson in 1879 (Proc. Am. Phil. Soc., XVIII, 289-316) called attention to benches along the valley of the Monongahela and its tributaries. He divided them into a higher series of twenty benches, and a lower one of five. The higher series he attributed to marine action. They are probably entirely above those under discussion, and later work on them has shown that they are obscure and are probably due to hard layers of rock. The lower series of Stevenson seems to include those under discussion, and he refers them to stream action, without going into details of development.

Some effects of glacial action in Iceland

Introduction The dominant geological features of Iceland are its glaciers and its volcanoes, both of which are developed on a tremendous scale and afford unusual opportunities for detailed study. The island itself is essentially an uplifted plateau country, averaging 500 to 700 meters in elevation, and consisting in large part of basaltic lava flows and associated tuffs and breccias. Fringing this plateau at different points are lowland coastal strips, whose total area is nearly one-fifteenth of that of the entire island; to these all habitation is practically confined, the rest of the island being a barren waste of lava and glacial debris, devoid of forests, and even vegetation, and worthless from an economic standpoint, but valuable to the geologist because of its excellent exposures. Soundings by the Danish government have shown that these lowland coastal areas, in north and west Iceland especially, extend seaward as a coastal rock shelf 100 . . .