Seaward Slope Research Articles

The South-Norwegian Piedmonttreppe of W. Evers

An interesting and important feature of the geomorphology of the northwestern coastal zone of Norway is the marked seaward slope which in many districts bounds the rocky skjaergard (or strandflat) zone towards the region of the banks where loose material, evidently largely of glacial origin, covers the rock surface. The slope has for long distances a fairly straight or regularly curved trend and has (since 1933) by the present writer been assumed to represent a fault zone along which the land mass is more or less uplifted.

SEAWARD PROFILE FOR RUBBLE MOUND BREAKWATERS

For several years, some coastal engineers have been aware that the seaward face of rubble mound breakwaters of the common trapezoidal cross-section is conducive to relatively severe wave action and possible damage to the breakwaters. Further, it has been suggested that a preferable seaward profile would be that composed of three straight lines, with the middle line at a relatively small angle with the horizontal, to form what might be thought of as abroad berm. In order to arrive at a more realistic knowledge of seaward profiles for which wave intensity and likelihood of breakwater damage are minimal, a laboratory study of shallow-water wave action on rubble breakwaters was initiated at Auburn University, It is hoped that such knowledge will lead to design procedures which will result in (a) less violent wave action, (b) less structural damage, and (c) the possible use of smaller stones. Thus far, the study has been devoted to shallow-water waves of two types, steep, smooth waves and spilling breakers, acting, with normal incidence, upon breakwaters constructed of various materials and having an initial seaward slope of 1 on if. For each set of conditions, the stable seaward profile was determined. Through dimensional analysis and curve fitting, an effort was made to describe the stable seaward profiles in terms of physical quantities which influence the profiles. It is the authors1 belief that the results of this study will be useful in leading to more rational design procedures.

Oriented wave-splash fretwork in sandstone

A fretwork of erosion pits can be observed in 2 littoral exposures about 1/4 mi NW. of Eastern Point and 1 mi E. of Newport, Rhode Island. The shoreline is approximately parallel to the strike of the formations displaying the fretwork; the beds dip in a series of cuestas gently seaward. The fretwork is present on the dip slope of the second ridge back from the shoreline and only on the upper part of this slope. The pits are oval and oriented with their long axes in the direction of dip. The pits do not vary greatly in size and their density is about 20/sq ft. It appears that storm waves play an important part in forming the pits. Waves of translation strike the seaward dip slope barrier and splash forward in an arcuate path and hit with great force against the top of the second dip slope. Fretwork does not appear elsewhere in the vicinity where exposures of the same lithology are acted upon only by atmospheric weathering processes.

Spur and Groove Formation on the Florida Reef Tract

ABSTRACT On two Florida reefs, submarine reef 10-12 feet high and up to 50 feet wide were dissected with explosives so that internal structures could be examined. Millepora and alga-coated were found to be composed mainly of in-situ coral (Acropora palmata). Comparison of A. palmata with encrusted suggests that a new interpretation of spur and groove formation is necessary. A. palmata growing in less than 20 feet of water on the seaward slope of reefs which face prevailing seas modifies its growth form so that the branches can accommodate the forward thrust of impinging waves. The branches become oriented in the direction of wave movement, and degree of modification is proportional to the wave strength. Continued unidirectional growth causes individual colonies to coalesce into fingerlike that project as much as 200 feet into oncoming seas. These living spurs die from crowding when they reach the surface and subsequently become completely masked with calcareous algae and Millepora. Moving sand, in the grooves between spurs, prevents coral attachment, and periodic hurricane seas remove accumulating debris derived from the overhanging walls of adjoining spurs.

Carbonate Cycles: Lower Pennsylvanian Marble Falls Formation, Mason and Kimble Counties, Texas: ABSTRACT

Samples from detailed measured sections were successfully classified by using Folk's descriptive limestone classification. Later in the investigation genetic rock categories (facies) that reflect ecologic environments were recognized and classified separately. The nine facies are shown in the following table. Table A transgressive facies tract can be identified, comprising four depositional areas: (1) nearshore and tidal flat, bearing the mottled facies; (2) middle shelf composed either totally of the churned dark fragmental facies or of Ivanovia banks with the churned dark fragmental facies to landward and the light fragmental facies to seaward; (3) shelf edge with algal banks or knolls, the tubular alga facies in deeper or protected areas, the Komia facies in turbulent or shallow areas; (4) seaward slope bearing the laminated dark fragmental facies grading seaward to the shale facies. The regressive facies tract begins with the seaward migration of the mottled facies and the lateral expansion of the Komia facies. It culminates on the shelf with the mottled facies and Chaetetes facies which developed on a surface of bypassing, and on the slope by deposition of debris transported from the Komia facies. Cycles have four phases: (1) minor transgression with shale at the base overlain by a poorly developed regressive facies tract; (2) slight regression with a poorly developed regressive facies tract; (3) major transgression with well developed transgressive facies tract; (4) major regression with well developed regressive facies tract. End_of_Article - Last_Page 376------------

THE "TETRAPOD"

The Tetrapod was invented twelve years ago and the first breakwater with a Tetrapod protection was built eleven years ago. It is felt that a review of the results since obtained with these artificial blocks may be of some interest, preferably in the form of an objective practical examination of the behaviour of Tetrapod-protected structures during the past few years, and of the way in which they have stood up to bad weather during the period. First, however, a brief description will be given of the development of the Tetrapod and the Tetrapod technique.
 Most breakwaters are of the rubble-mound type, because of the very good hydraulic properties of this type of design ; the seaward slope, roughness and "porosity" of their facings are generally such as to ensure the gradual destruction of wave energy, reduce wave overtopping and reflection and minimize toe erosion risks.

Patterns of Distribution of Sugar Maple, Acer saccharum Marsh., in Northern Cape Breton Island

An investigation has been made of the distribution patterns of Acer saccharum Marsh. on, and in close proximity to the limit of the range of the species in, northern Cape Breton Island. The limit of the range of the species cannot now be clearly delineated at sea level, but at greater elevations varies from altitudes of the order of 800 feet on seaward slopes to 1300 feet inland. In both primeval and second growth areas the density and dominance of the species vary widely, with a trend toward lower stocking with increasing altitudes. In some areas the limit of the range is marked by widely scattered trees whereas in others the density of the species is fairly high. Irrespective of stocking, there is no gradual transition in size toward a depauperate form or a marked decrease in vigour upon approaching the limit of the range of the species. On the basis of present evidence it is difficult to decide whether the limit of the range is stationary, advancing or retreating.

EXPERIMENTAL STUDIES OF SPECIALLY SHAPED CONCRETE BLOCKS FOR ABSORBING WAVE ENERGY

Laboratory tests were performed to determine wave energy absorbing ability of and stability characteristics against breaking waves of various shaped pre-cast concrete armor units used for protective cover layers on the seaward slopes of rubblemound breakwaters and for parallel dykes placed the offshore sides of seawalls. A new shape of armor units, a hollow tetrahedron concrete block with a porosity of 25 percentages in the body was proved to have better characteristics for wave energy absorbing ability and attenuation of wave run-up, as well as for stability against breaking waves also than tetrapod or other armor units used up-to-date.

Yamacraw Ridge, Pre-Cretaceous Structure beneath South Carolina-Georgia Coastal Plain: ABSTRACT

In the process of making alongshore and offshore seismic refraction studies of the geologic structure beneath the submerged Atlantic Coastal Plain from north of the Cape Fear arch in North Carolina to the vicinity of the Florida-Georgia boundary, it was noted that the measurements between Charleston, South Carolina, and Doboy Sound, Georgia, indicated that the basement (pre-Cretaceous) surface sloped towards the continent rather than towards the ocean. This reversal in the normal seaward slope of the basement surface was interpreted as being caused by a basement ridge, and named the Yamacraw Ridge of Meyer and Woollard. This past year it was possible to investigate this area End_Page 1254------------------------------ more fully and 12 reversed seismic refraction measurements were made in the emerged Coastal Plain area lying between Ridgeland, South Carolina, Walthourville, Georgia, and the coast. These measurements plus the previous seismic measurements in the submerged Coastal Plain area and well data, show that the Yamacraw Ridge is a well defined topographic feature on the buried pre-Cretaceous surface and that it forms the eastern boundary of the northern portion of the South Georgia basin. The ridge has an overall length of about 90 miles and a width of about 25 miles. It strikes about 22° west of south and its axis coincides roughly with that of the present coastline. The ridge originates at the general basement level near Charleston, S. C., and has the form of a spur which plunges to t e south with about 2,000 feet change in elevation along its length. The cross-section relief over most of its length is about 1,200 feet. On the basis of the observed seismic velocity values (16,000-19,500 feet per sec.), the ridge is composed of varying crystalline rock material. On the landward side of the ridge there is a marked basement embayment and local deepening alongside the ridge. This trough-like depression on the basis of the seismic velocity value (15,000-19,000 ft. per sec.) appears to be floored with crystalline rock material. The basement surface at the head of the trough is very irregular with indications of two incised valleys extending southward from the basement plateau area in South Carolina that stands about 3,000 feet above the floor of the trough in Georgia. In vi w of the relief and physical form of the Yamacraw Ridge it is suggested that it is of tectonic origin. The available well data suggest the ridge was completely buried before the end of Lower Cretaceous time. Because of the discontinuous nature of the seismic horizons in the overlying sediments plus the scarcity of well data it is not clear whether there has been any tectonic movement associated with the ridge since its burial. End_of_Article - Last_Page 1255------------

Subsurface Geology of North Carolina-South Carolina Coastal Plain from Seismic Data

Sixty new seismic-refraction measurements on the Coastal Plain of North Carolina and South Carolina were made to fill gaps in existing well and geophysical data and to make a more comprehensive study of the nature and structure of the Coastal Plain floor. Thirty-nine measurements were made on the adjoining Piedmont Province to determine seismic velocities of specific rock types, thus aiding the assignment of lithologic types to basement velocities observed on the Coastal Plain. Seismic velocities observed for gneiss, schist, slate, and granitic rocks range from 15,900 feet per second to 19,200 feet per second (4.8 to 5.8 km./sec.); diabase velocities averaged 22,500 feet per second (6.8 km./sec.); Triassic sediments from 10,400 to 14,500 feet per second (3.2 to 4.4 km./sec.); and the highest velocity correlated with Cretaceous Coastal Plain sediments is 9,600 feet per second (2.9 km./sec.). The following conclusions are based on these studies. 1. Because basement lithologic trends and velocities are similar to those in the Piedmont, confirmed by deep wells, it is apparent that the Piedmont complex extends under the Coastal Plain sediments as far east as the present coast. 2. The Carolina Slate belt extends under the Coastal Plain and reaches a maximum width, 80 miles, in North Carolina, though the Triassic Deep River basin is in the middle. An eastern slate belt with northeast strike is postulated midway between the Fall Line and the coast under the Coastal Plain sediments. 3. The buried Florence Triassic basin is approximately 40 miles long on an east-northeast strike and limited in width to 13 miles. A new buried Triassic basin is postulated to extend from near Raeford into Johnson County, North Carolina. 4. The Cape Fear arch is a prominent basement structure with a seaward slope of 13 feet per mile on the axis. It is not reflected in the sea-level basement surface contour near the Fall Line. Sedimentary record suggests differential movement at least twice since Cretaceous time. 5. The pre-Cretaceous basement is a surface of erosion with topographic relief on the order of 200 feet. 6. The break in basement slope in eastern North Carolina must be projected seaward of Cape Fear and the South Carolina coast. 7. There is the suggestion of an east-west syncline superimposed on the steeper basement slope in eastern North Carolina and its existence is supported by a similar structure in the Coastal Plain sediments based on an earlier seismic-reflection surve .

GEOPHYSICAL INVESTIGATIONS IN THE EMERGED AND SUBMERGED ATLANTIC COASTAL PLAIN

The results of a series of refraction profiles made over the continental shelf south of Nova Scotia and extending down to the adjacent deep basin are reported. The resulting geologic and crustal sections show the manner in which the gradation from continent to ocean takes place. The Coastal plain sediments reach a maximum thickness of around 20,000 feet on the gently sloping area at the bottom of the continental slope and thin further seaward. The crystalline basement of metamorphic rocks and granites over Nova Scotia gradually thins under the continental margins and pinches out toward the ocean basins. It drops abruptly under the continental slope from 5000 feet to 20,000 feet. The Mohorovicic discontinuity is measured on a single profile at a depth of 52,000 feet under the continental rise.

Influence of Submarine Canyons on Intrusion of Ocean Water into Fresh-Water Aquifer: ABSTRACT

Detailed hydrologic studies along the California, coast reveal that important fresh-water aquifers are exposed in submarine canyons or, if not exposed, are in hydraulic continuity with the ocean in the canyons. In the typical aquifer, which has a low-angle seaward dip, the effect of submarine canyons is to produce submarine outcrops abnormally close to shore. Under natural conditions, especially during wet cycles, the piezometric surface had a strong seaward slope and fresh water escaped at the submarine outcrops, especially those in the submarine canyons. The volume of stored fresh water in the submarine extensions of the aquifer is reduced by an amount proportional to the volume of the End_Page 187------------------------------ aquifer removed during the formation of the canyon. Accompanying excessive pumping of the aquifer will be the development of a landward slope of the piezometric surface and the intrusion of ocean water into the submarine area of the aquifer. The first water wells abandoned because of ocean water will most likely be in the vicinity of the submarine canyons. End_of_Article - Last_Page 188------------

Organic Growth and Sedimentation on an Atoll

An atoll is a composite reef made up of a number of distinctive reef types-windward reefs, leeward reefs, and lagoon reefs. Most of these are zoned relative to prevailing winds and currents. Organic growth, erosion, and deposition of sediment influence each of these zones, but in each the balance of forces operating at the present time may be roughly appraised. Some reef zones appear to be making headway against the sea, others appear to be essentially in a state of equilibrium, while still others are being eroded. Organic growth is the source of all the materials that make up an atoll. Some of the skeletons of the reef-building organisms remain in position of growth after death, but a much larger proportion are broken up by physical and organic agencies to form sediments that are deposited on the seaward slopes or in the lagoon. So long as organisms live on an atoll, it continues to grow, but it grows mainly by the accumulation of clastic sediments.

A NEW SPECIES OF INCISALIA FROM SOUTHERN CALIFORNIA (RHOPALOCERA, LYCAENIDAE)

The opening of a new highway along the coast from Monterey to San Luis Obispo, California, made it possible to collect in a hitherto rather inaccessible region. In 1938 Dr. Michael Doudoroff of the Hopkins Marine Station, Pacific Grove, California, took near Monterey, a few badly worn specimens of an Incisalia which he believed to be new. Returning the ensuing year in June and following the highway south about thirty miles below Carmel, he stopped near Big Sur, Monterey County, and there, after rather strenuous collecting on the precipitous seaward slopes of the mountains, he succeeded in taking a small series (eleven males and two females) of these butterflies. These he very kindly sent to me for determination.

Coffee Plantations of Brazil: A Comparison of Occupance Patterns in Established and Frontier Areas

The form of the coffee region reflects the advance of a frontier.1 A century and a half ago coffee was an experimental crop on coastal lowlands near Rio de Janeiro and Santos, narrowly confined between the sea and the escarpment of the Serra do Mar. Then, leaping the first mountain barrier, whose rugged seaward slope is still forest clad and unproductive, coffee began to flourish in the more congenial trough back of the coast range, particularly in the valley of the Rio Parahyba, where there are slopes and terraces more than a thousand feet above the sea. Here plantations still persist. But this also is a narrow strip of mountain-bound land. The trough extends southwestward beyond the head of the Rio Parahyba, though here it is hilly and infertile. This unproductive section, where the city of Sao Paulo now stands, is opposite a low and narrow part of the Serra da Mantiqueira giving easy access to the least rugged and most fertile part of the highland region beyond the mountain ranges. Here a century ago coffee leaped the second mountain barrier and established itself in the Campinas district, the threshold of a region of rolling uplands just within the tropics, two or three thousand feet above the sea, hot and humid in summer, warm and less humid in winter, diversified in soil, cut by stream valleys leading northwestward to the Rio Parana, toward which the plateau surface gradually descends.

ON THE SUPPOSED RAISED BEACH AT SALTBURN

(Read November 26th 1919.) The supposed presence of a Raised Beach of Post-Glacial age at Saltburn, at 35 feet above high-water mark, has afforded one of the minor problems in the geology of the Yorkshire Coast. The ‘beach’ was first described by Dr. W. Y. Veitch in the Proceedings of our Society for 1883 (N.S. Vol. VIII., pp. 221–6), and was referred to shortly afterwards by Mr. G. Barrow in his memoir, ”The Geology of North Cleveland” (Mem. Geol. Surv., 1888, p. 71). Dr. Veitch describes the ‘beach’ as “a band of alluvial sand containing shells and fragments of shells,” of which six kinds are mentioned, all common on the present shore ( Purpura, Littorina, Trochus, Lachesis minima and Cypraea europaea ); and states that it was exposed in the steep drift-slope below Saltburn in operations by the Saltburn Improvement Company, the deposit “extending 70 or 80 yards from the bridge up Saltburn Beck, where it abruptly comes to an end.” He also found shells at about the same level “south” [east] of the beck, on the seaward slope of Cat Nab, and considered that they indicated a continuation of the beach. Mr. Barrow gives practically the same particulars, and endorses the view that the deposit represents a Raised Beach, though he notices the abnormal circumstance that a beach of this kind should be preserved in a perishing cliff of soft Glacial beds and should be absent from the neighbouring rocky headland of Huntcliff, composed of much more durable Liassic strata.

The Tsakonian Dialect.—I

The area over which the Tsakonian dialect is spoken lies on the east coast of the Peloponnese between the Parnon range and the sea. Its northern boundary is roughly the torrent which, rising on Parnon above Kastánitsa, flows into the sea near Ayios Andréas, its southern the torrent which, also rising on Parnon, passes through Lenídhi to the sea. A mountain range stretches along the coast from end to end of the district, reaching its highest point (1114 metres) in Mt. Sevetíla above the village of Korakovúni. Between Tyrós and Pramateftí, the seaward slopes of this range are gentle and well covered with soil. Behind these coast hills there stretches a long highland plain, known as the Palaiókhora, which, in the north, is fairly well covered with soil, but gradually rises towards the south into a region of stony grazing land, and terminates abruptly in the heights above Lenídhi. The high hill of Oríonda rises out of the Palaiókhora to the west and forms a natural centre-point of the whole district. Behind it stretching up to the bare rock of Parnon, is rough hilly country, cut here and there by ravines and offering but rare patches of cultivable land.

Reports on the Marine Biology of the Sudanese Red Sea.-XVIII. A Physical Description of Khor Dongonab, Red Sea.

SUMMARY 1 There have been three successive lines of barrier reef along the Red Sea Coast, which, by continual uplift, have become: 1 A range of sandstone hills rising from the alluvial maritime plain; 2 A fringe of limestone along the present coast-line; 3 The present barrier system. 2 These three ridges were formed by folding and faulting of sedimentary-rocks which overlay the bases of the Archean hills at the time of the great movement which opened the Red Sea section of the Great Rift Valley. 3 The northern ends of several sections of the present barrier reefs are elevated above sea-level, and examination of these, especially the one forming Rawaya Peninsula, and of the hills forming the maritime plain, enables us to reach the above conclusions. At the same time Rawaya gives evidence of a seaward movement as well as uplift, Khor Dongonab and some at least of the channels within the Barrier Reefs being recent fault-depressions, not merely the original anticlinal fold formed by the opening of the Rift Valley. The harbours and other fissures in the coast are due to the same secondary faulting. 4 The maritime plain has had two maxima of seaward extension, the first being before, the second after the growth of coral on the second and third barriers. Owing to elevation nothing has been added to its seaward slopes since the formation of the features of the coast by secondary faulting. 5 The filling in of valleys and the completion of the connection of the second barrier with the maritime plain has been largely due to blown sand. The process is continuing, an extensive plain near Dongonab showing perfect uniformity in its formation. The effect of climate and vegetation on the formation of the plain is described (Plate 34). 6 Of the possible mode of formation of the widely distributed gypsum deposits the theory favoured is by the evaporation of a shallow sea which is presumed to have existed before the deep Rift Valley was made. The recent and still continuing deposition of gypsum beneath the Rawaya salt field is an interesting actual example of this method. 7 The restriction of coral growth within Khor Dongonab, a very exceptional it' not unique state of things in the Red Sea, is shown to be the result of abrasion by silt-carrying currents. Considerable effects follow from comparatively feeble currents which curry very little sand, but that this is sufficient to prevent the fixation of coral larvae is borne out by the comparison of newly fixed spat of those mollusca which do flourish on these current-swept banks with those of the Aviculidae, e.g., which flourish on the coral areas. 8 That on its west shore Khor Dongonab is extending itself at the expense of the land in spite of the presence, in some abundance, of coral and Lithothamnia. The presence of these must not be assumed to imply the addition of material to a reef unless their growth can more than counterbalance the forces of degradation.