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Geosciences
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Adriatic Sea

From 1911 Encyclopaedia Britannica:

The Adriatic Sea (ancient Adria or Hadria) is an arm of the Mediterranean Sea separating Italy from the Austro-Hungarian, Montenegrin and Albanian littorals [in 1911] and the system of the Apennine mountains from that of the Dinaric Alps and adjacent ranges. The name, derived from the town of Adria, belonged originally only to the upper portion of the sea (Herodotus vi. 127, vii. 20, ix. 9 2; Euripides, Hippolytus, 736), but was gradually extended as the Syracusan colonies gained in importance. But even then the Adriatic in the narrower sense only extended as far as the Mons Garganus [the promontory projecting from Apulia into the Adriatic to form the ‘spur’ on the Italian boot] the outer portion being called the Ionian Sea: the name was sometimes, however, inaccurately used to include the Gulf of Tarentum, the Sea of Sicily, the Gulf of Corinth and even the sea between Crete and Malta (Acts xxvii. 27).

The Adriatic extends northwest from 40° to 45° 45' north, with an extreme length of nearly 500 m., and a mean breadth of about 110 m., but the Strait of Otranto, through which it connects at the south with the Ionian Sea, is only 45 m. wide. Moreover, the chain of islands which fringes the northern part of the eastern shore reduces the extreme breadth of open sea in this part to 90 m.

The Italian shore is generally low, merging, in the north-west, into the marshes and lagoons on either hand of the protruding delta of the Po River, the sediment of which has pushed forward the coast-line for several miles within historic times. On islands within one of the lagoons opening from the Gulf of Venice, the city of that name has its unique situation.

The east coast is generally bold and rocky. south of the Istrian peninsula, which separates the Gulfs of Venice and Trieste from the Strait of Quarnero, the island-fringe of the east coast extends as far south as Ragusa. The islands, which are long and narrow (the long axis lying parallel with the coast of the mainland), rise rather abruptly to elevations of a few hundred feet, while on the mainland, notably in the magnificent inlet of the Bocche di Cattaro, lofty mountains often fall directly to the sea. This coast, though beautiful, is somewhat sombre, the prevalent colour of the rocks, a light, dead grey, contrasting harshly with the dark vegetation, which on some of the islands is luxuriant.

The north part of the sea is very shallow, and between the southern promontory of Istria and Rimini the depth rarely exceeds 25 fathoms. Between Sebenico and Ortona a well-marked depression occurs, a considerable area of which exceeds 100 fathoms in depth. From a point between Curzola and the north shore of the spur of Monte Gargano there is a ridge giving shallower water, and a broken chain of a few islets extends across the sea. The deepest part of the sea lies east of Monte Gargano, south of Ragusa, and west of Durazzo, where a large basin gives depths of 500 fathoms and upwards, and a small area in the south of this basin falls below 800.

The mean depth of the sea is estimated at 133 fathoms. The bora (north-east wind), and the prevalence of sudden squalls from this quarter or the south-east, are dangers to navigation in winter. Tidal movement is slight. (See also Mediterranean.) For the "Marriage of the Adriatic," or more properly "of the sea," a ceremony formerly performed by the doges of Venice.

GENERAL REMARKS

From Coasts and Island of the Mediterranean Sea, Part IV. Government Printing Office (Washington, 1883), Chapter II. General Remarks — Adriatic Sea, pg. 16-36:

WESTERN AND EASTERN COASTS

The Adriatic Sea or gulf of Venice is the great expanse of waters which, branching off to the northwest from the main body of the Mediterranean sea, is bounded by Italy on the west and by the Austrian provinces and Albania on the east

The first of these names is derived from Adria or Hadria, founded in 1376 B.C. by an Etruscan colony, and once the most important town in the Adriatic, but now in ruins, some 15 miles inland, at the upper part of the gulf of Venice; the second name is from Venice, which was for centuries the chief city in the Mediterranean.

The Adriatic, from its southern limit, between cape Sta. Maria di Lucca and the island of Corfu, to its northern termination at the Venetian shore and the gulf of Trieste, is about 460 miles in length in a general northwest and southeast direction. From Brindisi, in Italy, and Durazzo, in Albania, the sea to the northwest is bounded by two almost parallel coasts, the general breadth being about 90 miles, and the greatest, between Fano and Novi, 110 miles. The narrowest part at the entrance is between capes Otranto and Linguetta, distant apart rather less than 40 miles.

The two sides of the Adriatic sea differ entirely in aspect and character, the eastern shore being generally rocky, replete with islands and ports bold of approach, but deficient in inhabitants, provisions, and in many parts in fresh water; the western coast, on the contrary, is comparatively shallow, and almost without any large ports, yet in most parts populous and abounding in provisions, water, and articles of trade. This peculiarity has so great an influence in the navigation of the sea that mariners cannot be too careful in making themselves acquainted with the advantages and inconveniences presented by the two coasts before they decide on their route.

Italian seamen frequently make use of the expression sotto vento, leeward, and sopra vento, windward, to designate the coasts of the Adriatic. These terms have reference to the direction in which the bora, or northeast wind generally blows; thus, the eastern is the windward and the western the leeward coast. [17]

The WESTERN COAST, as it will be termed throughout this work, is the Italian seaboard, beginning on the southeast at cape Sta. Maria di Leuca, and terminating on the northwest at port Buso, the entrance of the river Ausa, at the boundary between Italy and Austria [in 1911].

It is generally of little elevation, and trends in an almost straight northwest line to Ravenna, where it bends to the north, and forms the Venetian shore. Its uniformity is broken in three principal places: First, at mount Gargano or St. Angelo, near the Tremiti islands; secondly, at mount Conero, between Loretto and Ancona; and, thirdly, at the delta formed by deposits at the mouth of the Po. The former two, which are high and terminate each in well defined elevations, form excellent landmarks. The celebrated chain of the Apennines runs almost parallel to the Abruzzo coast, between the two elevations. The summits of mount Corno or Gran Sasso d'Italia, 9,500 feet high, and of mount Maiella, which are its most elevated points, are remarkable, and may be seen at a great distance in clear weather.

The shore consists chiefly of sandy beaches, and, with the exception of the two points where the land rises, the soundings along it are regular, with an approach of considerable less boldness than on the opposite coast. Roadsteads are scarce; there are many harbors, of which a few only are capable of admitting large vessels, but which are nevertheless suitable to the busy export trade carried on along the thickly populated shore. The most important products exported are corn, rice, fruit, oil, wine, cotton, wool, silk, and salt [in 1911]. The great lakes between the village of Peschichi and the town of Termoli, named Varano and Lesina, have long been celebrated for the abundance, variety, and excellence of their fish; their margins are said to be unhealthful.

A great number of rivers and streams intersect the northwest portion of this coast from Ancona to the river Isonzo, near the head of the gulf of Trieste, and bring down considerable quantities of sand and mud, which encumber the shore with shoals and obstruct nearly all the harbors. The Italian coast is, however, always easily navigable in fine weather, and can be approached sufficiently near for the recognition of all its most conspicuous objects, which may be generally seen at a distance of 10 to 12 miles.

The EASTERN COAST embraces the Austrian dominions of Istria, Croatia, Dalmatia, Ragusa, and the mouths of the Cattaro, and the Turkish province of Albania. It is in general high and picturesque, with almost perpendicular cliffs, and very deep water along shore. To these features, however, there is an exception between cape Linguetta and the gulf of Drin, where the shore is low and sandy and the water less deep. This coast runs almost southeast and northwest, and in some places [18] forms deep bays. From Ragusa to cape Promontore, it is entirely bordered by islands, rocks, and shoals, which render the navigation intricate and often unsafe, when overtaken by the bora.

Mariners, notwithstanding, give the preference to the eastern coast, particularly during the bad season, as it has some good harbors, and in many parts affords shelter in stress of weather, while on the western coast the only ports are those of Brindisi, Manfredonia, and Ancona, which are often of difficult access.

The water on almost every part of the coasts of Istria, Croatia, and Dalmatia to the gulf of Drin, and between the islands, is generally deep very near the land; but between the gulf of Drin and cape Linguetta the shore is not so bold, being bordered by shallow water, and soundings extend some distance seaward.

The greater part of the eastern coast is barren and uninhabited, and the trade is insignificant; with the exception of Trieste, Fiume, and Valona, the inhabitants of almost all the towns and islands are poor, and provisions, including water, are difficult to be obtained.

The basin of the Adriatic is said to be slowly diminishing in size. There are numerous evidences of encroachment of the land, on the sea, through deposition of soil by rivers. Owing to the peculiar situation of the high mountains of Illyria, the head of the gulf of Venice receives all the waters flowing from the southern declivities of the Alps and the Carniola mountains, situated between the Po and the Isonzo; here also flow out the Adige, Brenta, Piave, Livenza, Tagliamento, and numerous minor streams, each carrying down in freshets great quantities of alluvium, mud, and gravel, into the lagoons, and form vast shoals which border the intervening shore.

The effect of this accumulation is particularly perceptible along the whole coast between Maestra and Sdobba points. Thus Aquilea, which once may have stood near the sea, has long been an inland town, while the harbors of Liquentio, Romantino, and Timaro, said by Pliny to have existed on this coast, have entirely disappeared. Adria, which was a station for the Roman fleet, is now 15 miles inland. Another town of the name of Spina, formerly bordered by quays, is now completely buried under the sands. Ravenna, built on islands and piles on the margin of the sea, was, in the time of Theodosius the Great, a military port, subject to the influence of the tide; it is now nine miles inland, in the midst of gardens and fields. Portus Classis, its ancient harbor, has become a marsh four miles from the sea, from which it is separated by the Pineto or pine forest. The flat lands are subject to malaria in summer.

The color of the Adriatic sea, when undisturbed by any accidental or [19] local cause, is darker than that of the Mediterranean, being of a greenish hue. The specific gravity at its mouth was found by Captain Smyth to be 1,0291, at the depth of 40 fathoms.

SOUNDINGS

In general, throughout this sea, the soundings along shore are according to the exterior character of the coast. Where the land is elevated and rocky, deep water will be found, and vessels may approach to a prudent distance; where it is low, level, and sandy, the depth is small. The shoalest water is along the Venetian shore and at the mouths of the Po.

The nature of the ground follows an almost uniform rule along the whole of this coast; fine sand is found near the beach, then sand mixed with mud, and lastly mud; in some places only the bottom is clay, covered with soft mud, and sometimes marl intermixed with sand and clay. The distance to which these several zones extend varies according to the strength of the current inshore and its extension seaward. Mud bottom, suitable to anchorage, will almost always be found at a distance of from one to three miles from the land, and the nature of the bottom is mud nearly everywhere towards the middle of the Adriatic.

The researches made at the commencement of the last century, have shown that but little difference exists between the matter of which the nearly horizontal layers of the bed of the Adriatic is composed and that of the surrounding continent, islands, and rocks. A white marble of uniform grain, resembling the substance of the Istrian, Morlacca, and Dalmatian countries, often occurs; in some places are found gravel, sand, and other matters, more or less metalliferous. Near the beginning of last century, Vitaliano Donati invited attention to the formation of a concretion of crustaceans, testaceans, and polyps, partially petrified, and intermixed with earth, which is said to be increasing, and may have the effect, so far, of gradually decreasing the depth.

According to Strabo's account of Adria the encroachment of the sand may be approximately estimated at about nine miles in 2,000 years.

According to M. de Prony the sands have advanced nine miles since 1604; in the twelfth century the sea was from six to seven miles distance from Adria; at the close of the sixteenth century, when a channel was opened for the river, the most advanced projections of its alluvial deposits were 12 or 13 miles from Adria. This would give a mean annual advance of about 27 yards. The extremities of these alluvial deposits being at present about 22 miles from the meridian of Adria, their annual encroachment may be taken at about 77 yards.

An extensive bank of mud intermixed with chalky and other matter, which by gradual growth may eventually form an island, has risen in [20] the middle of the gulf of Venice, where the depths are less than in other parts of the Adriatic.

A depth of about 536 fathoms is found in the middle of the entrance, between capes Linguetta and Otranto. The line of deepest soundings yet obtained runs thence about 30 miles south of the island of Meleda, and south of Lagosta, between Cazza and Pelagosa, and then takes a northwest, direction; near Pomo islet the depth is about 100 fathoms; it then approaches the Dalmatian, coast, and passes about 10 miles south of Zuri and Incoronata islands, whence it takes nearly a middle course, bordering on the eastern shore of the sea, to the parallel of cape Promontore; at 25 miles to the westward of which the depth is 25 fathoms, gradually decreasing towards the gulf of Trieste.

In the gulf of Venice the depths are generally gradual, and vary between nine and 25 fathoms; relatively to the rest of the Adriatic this part appears to form a submarine plateau, which may strictly be considered a continuation of the great plains of Lombardy and Friuli.

ISLANDS

Almost all the islands of the Adriatic are along the eastern coast between Ragusa and cape Promontore. They ate numerous and appear to have originated in the breaking up of the lower grounds by some violent action, which has left their limestone summits above water. By the salient position of the promontory terminating in Planka point, they are divided into two distinct groups. The principal islands lying southward of Planka point are Meleda, Curzola, Lesina, Brazza, Lissa, and Lagosta; to the northward of the point the most important are Zuri, Incoranata, Grossa, Cherso, Veglia, Pago, and Lussin.

Their general direction is nearly northwest and southeast; they are all narrow in proportion to their length, and form various channels called after the nearest adjacent island, and which, being bold, with but few hid. den dangers, give a variety of secure passages between them. The islands are replete with ports and harbors, some of which are of considerable capacity.

Near Gargano head, on the Italian coast, is a group of four islets, called the Tremiti islands, on the south side of which good shelter from the bora may be found. south of Lissa is the isolated rocky isle of Pelagosa, nearly in the middle of the Adriatic, and between it and the Tremiti islands the low and dangerous Pianosa islet; lastly, to the west-northwest of Lissa are Pomo, a high pyramidal rock with a dangerous shoal off its north end, and between Lissa and Pomo is St. Andrea islet.

GULFS

The small gulfs of the Adriatic are: the gulf of Trieste, in the most northern part of the sea, extending 20 miles in an east-northeast direction, and comprised within the limits of Tagliamento point on the [21] north, and Salvore point in Istria, about 19 miles apart. The depth of water does not reach 15 fathoms. The shallow gulf or bay of Venice, between Tagliamento point to the northeast, and Maestra point on the southwest, is also about 20 miles deep, and, like the gulf of Trieste, the depth of water does not exceed 15 fathoms.

The gulf of Quarnero is separated by the peninsula of Istria from the gulf of Trieste; it extends about 60 miles from northwest to southeast, and is contained between cape Promontore, the land of Nona, and Grossa island. It is in great part occupied by islands, from the four most important of which, Cherso, Veglia, Arbe, and Pago, the gulf is said to derive its name.

The small gulf of Cattaro, a peculiar formed basin indented and surrounded by steep cliffs, is on the eastern coast of the Adriatic.

The gulf of Manfredonia, the only one on the Italian coast south of Gargano head, and between that and the town of Trani, is about 17 miles deep east and west.

WINDS

The navigation of the Adriatic in a sailing vessel requires care, owing to the liability of being caught in a gale without sea room, and therefore the winds demand constant attention, especially during the winter. During the summer they are light and variable, with frequent calms and occasional squalls from the northward; in winter they are almost always from north or northeast, or from southeast, with thick fogs and rain.

The winds are very variable at the mouth of the Adriatic; they are steadier in the middle of the sea; but still more variable at its northern extremity, in the gulf of Venice; it is not unusual to see vessels, near the Po and Trieste, steering towards each other with totally opposite winds.

The weather is exceedingly unsettled along the eastern coast between the gulfs of Trieste and Cattaro; in summer calms, thunder, waterspouts, and the hot wind, which the Sclavonians call youg, are frequent; and in winter heavy northerly blasts of the bora, with thick fogs and squalls.

The navigation of the western coast is nearly always hazardous in winter, but during summer it is generally without difficulty, fine weather with alternate land and sea breezes prevailing.

The most frequent winds in the Adriatic are from northeast to east-northeast, and from southeast to south. The former are the most severe, and require constant and careful attention; the latter, although less dangerous, are troublesome on account of the sea which they raise and the rain which accompanies them; winds from southwest to northwest blow occasionally, but they are [22] less frequent than those from southeast to northeast, and the duration of westerly to that of easterly winds may be considered as one to three.

Winds from southward, and especially from southeast, are prevalent at the entrance of the sea, whilst those from northeast and northwest, particularly in the fine season, are most common in its northern part; it often happens that fresh breezes from northeast, northwest, and southwest blow in different parts at the same time.

The light breezes are generally from eastward, as in most parts of the Mediterranean; they have the effect of mildewing the sails, if the precaution of airing frequently in westerly and in northerly winds be not taken.

Bora

The name bora is generally given in the Adriatic to winds between north-northeast and east-northeast It is very dangerous and greatly feared, as it rises suddenly and blows with extreme violence; generally, and especially in winter, it blows with the greatest strength after a strong gale from southeast and is most persistent and violent on the eastern coast. Its general direction is across the Adriatic, and the limited breadth of this sea is one of the causes of the risk attending it, for a vessel unaided by steam and unable to carry sail may be rapidly driven towards the coast of Italy, where there is scarcely a place of shelter for large vessels.

Vessels generally let fly everything to receive the first blast, then bear up to the southward for any port they can fetch, or remain under bare poles till it is exhausted.

Off the gulf of Cattaro the bora, although less violent, sometimes renders it impossible for vessels to carry any sail, even when overtaken at a short distance from land; very often in this part of the Adriatic, on standing out at once, the wind will be found more moderate, and a vessel may then run for a shelter or keep at sea.

In winter, this wind is to be feared, especially in Vrullja bay or cove near Makarska, at the mouth of the Narenta, and off the valley of Giulana, Sappioncello; it is also usually exceedingly fierce between Zuri island and Planka point, from the high land in the vicinity of Sebenico.

In the channels of the Quarnero, and at the entrance of this gulf, too much precaution cannot be taken; the bora here rushes down from the whole line of the Julian Alps with such irresistible fury that it is not only prejudicial to navigation, but extremely so to agriculture, which has in some parts been consequently abandoned; the chief part of the maritime trade of Fiume can only be carried on during the fine season, and the otherwise eligible haven of Porto Re is almost useless. Whole districts are rendered uninhabitable, and as not a bush nor a blade of grass can grow on the shores most exposed, local craft usually anchor off the parts where vegetation is most abundant. When Velebit Gebirge, [23] or the high mountains of Croatia, are capped by white clouds a vessel should not venture into the Quarnero.

The bora sometimes obliges vessels anchored in Trieste road to seek shelter under Salvore point and along the coast of Istria. It is the more dangerous in the channels of the islands, because it generally takes vessels on the beam and there is but little room; the mariner should at all times keep under the weather island, in order to be able to bear up.

It gives sufficient notice of its approach to an attentive observer to allow of precautions being taken. When small dark clouds are seen rising from the mountains of the eastern coast of the Adriatic, and taking irregular directions, and large white, round, isolated clouds gather on the tops of the high mountains of Dalmatia, a bora may be shortly expected, which will continue to blow until the former disappear, and the latter no longer adhere to the land. As a general rule, the clouds only leave the sides of the mountains when the wind loses its force and is about to cease.

The barometer is no positive guide, though it generally falls slightly on the approach of a bora, and at times corresponds with the violence of the coming wind, yet it generally rises during the gale. If to the fall of the mercury are added any of the indications above mentioned, there should be no hesitation in taking every precaution that prudence may suggest.

The heaviest boras are at times announced some hours before they burst by a dense black cloud on the horizon in the northeast, with light fleecy clouds above it, a rather lurid sky, and an unusual stillness of the atmosphere. The general direction of these gales is between north and northeast, and the ordinary continuance about fifteen or twenty hours, with heavy squalls, thunder, lightning, and rain at intervals. The bora most feared is that which, after blowing in sudden gusts for three days, subsides, and then returns for three days longer.

It generally dispels any hovering clouds or fog, and when it blows with great force the weather is very clear; a few small round clouds moving rapidly being alone visible; if the atmosphere should not be cleared after 24 hours, the wind will probably continue a long time, or a south-easter will spring up. In winter it is frequently accompanied by thick fogs and snow, causing excessive coldness.

It usually comes on at the rising or setting of the sun, abating, or frequently ceasing, at noon or daybreak: but should it continue in force at these periods, it may be expected to last a considerable time.

In winter it is most persistent, sometimes blowing for nine, fifteen, or thirty days, with short intervals of calm, during which it is not prudent to make sail.

[24] In summer it seldom or never lasts longer than three days, and is then usually moderate; if it increases in strength, it is generally for a short time only, and after a great deal of rain; it has, however, some difficulty in rising as long as the mountains of the eastern coast are wet with rain; when it then occurs it is of short duration, and the force is generally in proportion to the dryness of the land. March, the end of May, and especially the early part of June, seldom pass without a gale.

The bora often succeeds a slight fall of rain following a long drought; should it not blow in such a case, southeast winds may be expected.

The bora at times does not admit of the use of a single sail, when a vessel cannot escape being set on the coast of Italy. Should it admit of any sail being carried, the tacks are so short that the vessel may get embayed on that coast, without much chance of beating off again.

In December, 1811, the French frigate Flora, of 44 guns and 340 men, was surprised by a bora, on her passage from Trieste to Venice, which threw her on the coast near Chiozza, where the captain and two-thirds of her people perished. In 1815 two merchant vessels which had anchored off the mole of Trieste were struck by a bora in the night, and foundered with all hands; and in 1820 the Monte Cuculi, a fine Austrian corvette of 20 guns, was met by a bora while under all sail, and instantly went down with the whole of her passengers and crew.

The bora is caused by the cold wind in the elevated valleys and mountains rushing down into the warmer basin of the Adriatic. At Trieste it comes down with fury by the pass in the Julian Alps, but its greatest strength rarely reaches beyond 30 miles from the shore.

Sirocco

Southeast or sirocco winds are common throughout the Adriatic; they are usually steady, and only reputed dangerous on account of the heavy sea, thick fogs, and rain which accompany them; when they occur in winter the land is entirely concealed from view. They are frequently succeeded by a fresh northwest breeze.

The indications are a very sensible mildness of the atmosphere, even in winter, and dark clouds settling on the summits of the islands and lofty mountains of the eastern coast; these signs occur some time before the wind, which generally passes gradually over the whole sea.

A swell from the eastward often precedes this wind, and at times lasts after it has ceased; this swell, and an increase in the strength of the regular current setting to the northwest along the eastern coast, with a rise of the sea above its ordinary level, are sure signs of a southeast wind.

The barometer always falls with a southeast wind, and generally with all winds from the southward; when it continues to fail with the indications described, a southeast wind may be expected to blow with great force.

[25] If after continuing some time the wind should die away, and be succeeded by a calm or by variables, and the signs above mentioned continue, a renewal may be soon expected.

It is more frequent in winter than in any other season, generally blowing alternately with the bora; between the two winds there is nearly always an interval of light variable wind.

It commonly lasts three days, and very seldom beyond nine days in winter. It comes on by degrees, and only blows with violence after thirty-six or forty hours; as its direction is right up the Adriatic, the sea gradually increases, the clouds become heavier, rain falls in abundance, and the weather becomes very foggy, especially in October, November, December, and January.

Sailing vessels near and outside the islands of the eastern coast may be in danger, should the southeast wind subside immediately after blowing hard and leave a heavy sea, which often occurs in the evening; when in this locality shelter should be sought for when clouds are gathering on the summits of the islands. The eastern coast between Ragusa and gulf of Drin is also dangerous, and especially off the gulf of Cattaro. On the whole of the western coast, and along the Venetian shore, where no shelter whatever is found, the sea breaks heavily.

In summer the southeast wind is never strong, and towards the middle of the Adriatic it generally alternates with light breezes from the east, and sometimes from the northwest In this season should the clouds which collect on the summits of the islands, particularly of Lissa, become detached, and rise in thick globular masses, a northwest wind may be expected to succeed.

When southeasterly winds die away in winter, spring, and autumn, they are generally followed quickly by those from west, and northwest to north, which bring fine weather.

The Siffanto

Besides the bora and sirocco, which are the two principal winds in the Adriatic, the southwest or siffanto, and southerly winds, prevail occasionally. The southwest wind is frequently violent, but does not last long; it sometimes shifts suddenly to the southeast; these sudden changes are very dangerous in the vicinity of the mouths of the Po, where they always occur in strong squalls called furiani, with a heavy sea.

A southerly wind is often preceded by the same signs as a southeasterly wind, and it also gives rise to a high sea. Winds from south and southwest are little felt among the islands, which afford protection from them; and when they are light in the offing, calms are nearly always to be found within the islands. They do not last long, and are generally succeeded by westerly and northwesterly breezes. The Maestro or northwest wind is of rather frequent occurrence in the Adriatic, but mostly during the summer, on the western coast, and in the northern part of the sea; it is always followed by winds from southeastward.

On the eastern coast it generally rises about mid-day, and subsides towards evening, when it is commonly succeeded by land or by variable winds, which in fine weather sometimes continue after sunrise.

In the fine season a strong northwest wind occasionally succeeds a southeaster along the western coast; but it abates at night, and during the morning is generally succeeded by light land breezes.

Winds from northwest, north, and west do not raise much sea, and they always enable vessels to leave the Adriatic.

Local observations on the winds

At the entrance of the Adriatic the winds change with the seasons, being generally from south, southeast, and west, in autumn and winter, and from northeast and north in spring and summer. The latter may last for some time, but very seldom more than three successive days. westerly winds, though often blowing hard, with rain in winter, are not to be dreaded, as good shelter from them can be found. Winds from east and north sweep over the mountains of Epirus, which in winter are covered with snow, causing intense cold; those from the southward produce a suffocating heat, rendered still more disagreeable by rain and thick fogs.

The entrance of this sea is liable to very sudden gusts, and when it continues to blow hard the sea is short and confused, subsiding, however, with the wind.

On the eastern coast, from the gulf of Drin to the gulf of Quarnero, the bora blows almost constantly in winter with great violence. southeast winds, accompanied by thick fogs and rain, prevail on this coast during the autumn, and often render impracticable approach to the gulf of Cattaro and the adjacent shores.

Land breezes of variable strength are common at night on the eastern coast, during the whole year, and at the entrance of many ports continue for a long time after sunrise.

In the neighborhood of the Narenta, when the clouds, which generally cover the top of mount Bukavac, rise and break, the bora may confidently be expected with hurricane strength; if these clouds are scattered in the sky, the bora is already blowing near the land, though it may not have reached the offing. Very intense cold is experienced in winter in this part of the Adriatic on the approach of the bora.

A curious phenomenon, which occurs in the mountains of Montenegro, may be noted here. In the most steady season of the year, in the finest day, and with the purest atmosphere, when not a speck of [27] cloud is perceptible, thunder is heard among the mountains, and it is observed that at these times all the rivulets and springs in the neighborhood discharge a greater quantity of water than usual.

In the gulf of Quarnero the bora is the prevailing wind; there, more than at any other part of the eastern coast, it renders navigation very dangerous, and between cape Promontore and Unie island it gives rise to formidable whirling gusts and a heavy sea. It sometimes blows furiously in Morlacca channel, along the Croatian coast, and as far as the middle of the gulf, while there is a dead calm at the islands at its entrance and in the offing. It is easy to know from the appearance of the Velebit Gebirge, the high mountains of Croatia, whether the bora is blowing, or about to blow, in Quarnero gulf. When the summit of this chain of mountains is covered with large whitish clouds, and small dark clouds are seen to rise from the gorges, every possible precaution should at once be taken against a gale.

The bora is less violent in summer, when it is called the borino; it abates chiefly at the entrance of the channels in the vicinity of the coast of Croatia, where it is followed by a light breeze from eastward, which blows until about 9 o'clock in the morning; then, after an interval of calm, the wind sets in from northwestward until evening during nearly the whole of the fine season.

In the gulf of Quarnero the dark clouds which precede easterly winds alight first on the summit of mount Ossero, at the north end of Lussin island, then on Maggiore and Velebit mountains, after which they gradually cover the lesser elevations. In the winter the bora and the sirocco sometimes contest violently with each other for the mastery in this gulf; caution is therefore requisite in the navigation of these waters, and with southeasterly winds, even if blowing hard, any signs of the bora must be carefully watched.

The bora is almost constant in winter on the coast of Istria, where it sweeps along the shore. It is almost impracticable in a sailing vessel to take a harbor while it lasts, for on approaching land it is generally found to blow out of the inlets.

Southeasterly winds in winter become more southerly on reaching cape Promontore, but close to the land, along the western coast of Istria, they will be found drawing to the eastward.

Southwesterly winds are dangerous on the latter coast, upon which they blow and cause a heavy sea; although generally of short duration, the land becomes obscured, when it is difficult to take a harbor.

In summer, when the weather is fine, a light and variable breeze from northeast to east blows almost every morning, nearly throughout the gulf of Trieste; it generally draws to the west towards noon; then to the south, [28] and continues till evening. In this gulf two opposite winds sometimes blow at the same time with equal force — the one north of Salvore point, the other between cape Promontore and Rovigno; vessels should therefore always approach Salvore point with great caution if the sky be not clear in the northeast, which is a sure sign that the bora is blowing in the north part of the gulf.

In winter, on the western coast between Venice and Gargano head, the prevailing winds are the bora and sirocco, which blow alternately; if they last for any length of time the sea rises and the navigation becomes dangerous, particularly near the mouths of the Po.

In summer, on this coast, the winds are light and generally off the land during the night and until midday; then from the south or southeast till evening. The sea breeze on the Venetian shore usually comes on feebly and gradually, but sometimes springs up quite suddenly at the head of the gulf, accompanied by thick fogs; it is then of short duration.

In spring the winds here are variable; in autumn they are almost always from southeastward.

The southwest wind sometimes blows in violent squalls off mounts Conero and Gargano.

Off the coast between Gargano head and cape Sta. Maria di Leuca, the bora generally blows from the north except in a very heavy gale; an off-shore wind is frequent at night, while the bora continues in the offing.

From a meteorological journal kept at Venice for five years, it appears that at the head of the Adriatic southerly winds are most frequent during the summer months to September. The wind is seldom from the northward between April and July, and it is generally variable during fifteen days of each month of the year. It is to be observed that about twenty days of fine weather, with light breezes or calms may be depended on in any month of the year.

The rain-gauge shows that 32 inches of rain fell annually, of which 4 inches in September, and 6-1/2 inches in October, January, February, May, and December — periods at which southerly winds are not very frequent in the upper part of the gulf.

The range of the barometer is but small throughout; its indications should, however, be consulted in navigating the Adriatic. The mercury usually rises with winds from the northward, and falls with those from the south or southeast bora gales generally produce a momentary depression in the mercury; sometimes this fall is very slight, and far from adequately announcing the coming storm. Mariners should therefore be on their guard when it descends, though but little, especially if the fall be accompanied by the appearances already described as precursors of the bora. [29]

CURRENTS

A regular northwesterly current sets from the Corfu channel along the eastern coast, sweeps round the gulf of Venice, and thence, more rapidly, outward along the western coast. It is almost inappreciable beyond a distance of six to 10 miles from the shore. This general action is accompanied by a sufficient tidal influence to cause a variety of local sets called ligazzi, some of which prevail right across — a natural consequence of the outline of the Adriatic and the numerous islands.

The rate of the Adriatic current appears to be very irregular, varying in calm weather according to locality and season; it is least in summer, when there is scarcely any current on the Venetian or Italian shores as far southward as the Tronto river, but where it increases in strength, and at times runs at the rate of three miles an hour, its greatest speed being within three miles of the shore.

The currents in Corfu channel greatly influence those in the Adriatic. In this channel, and between the Ionian islands, the stream is remarkably affected by the wind, but generally sets to the northward.

There is sometimes in the Corfu channel a surface current to the southward, which is retarded of increased according to the force and direction of the winds in the offing. When it blows rather strong from from the north the waters set to the southward at the rate of 1-1/2 or two miles an hour, and a fall of three to four feet is occasioned. A southerly wind causes a rise to about the same amount, and the current then sets northwards. But this is not confined to the channel, although it is there the most marked, for over the whole Ionian sea southerly winds cause a rise of about a foot, and northerly winds a fall of about the same amount; if the winds are strong and continuous, the elevation and depression are greater.

At the entrance of the Adriatic, between Corfu and cape Linguetta, on the Albanian coast, the current generally runs to the northwest about half a mile an hour, increasing perceptibly as cape Linguetta is approached; it is generally greater with the winds from the southward.

The currents are very variable and frequently strong towards the middle of the entrance, where in fresh northerly breezes they set to west-northwest and west-southwest at the rate of three-quarters of a mile to a mile an hour; along the western coast between capes Otranto and Sta. Maria di Leuca the current is generally strong, except in calm weather and during the fine season when the wind blows directly on this coast. In a calm, at six miles from the land, the current sets about south by west at the rate of a mile an hour, and near cape Sta. Maria di Leuca at more than two miles. In fresh winds from the northwest they soon attain a strength of two, three, and even four miles and hour.

[30] The westerly direction of the current at the entrance of the Adriatic may be considered almost constant; at times, however, under the influence of winds from west and southwest, along the Ionian islands, and far as cape Linguetta, there is a set to the eastward of about a mile an hour, and even more between the islets northwestward of Corfu, where in December it has been found running north by east 1/4 east two miles an hour in a smooth sea, with a light southwesterly wind.

From Saseno island at cape Linguetta, the stream appears to divide into two parts, the inshore branch taking a northerly direction as far as the gulf of Drin, with an irregular and often scarcely perceptible rate, but which at times with southeast winds amounts to one and 1-1/2 miles an hour. This current follows rather regularly the coast as far as cape Rodoni; its greatest velocity being near the headlands, but in the bays it appears to be diffused. Beyond the gulf of Drin it follows the direction of the coast.

The other branch from Saseno island runs generally in the direction of Meleda island, with a velocity varying in calm weather from half a mile to two miles an hour. When influenced by southwesterly winds, and even in calms, this current frequently sets northeastward, about three-quarters of a mile an hour. Between cape Linguetta and Meleda island, southing in the currents is rarely found; it is only met westward of this line, where it increases as the coast of Italy is approached, especially with a northerly breeze.

Off the gulf of Cattaro, the inshore current of the Albanian coast is deflected by an outset, caused by southeast winds, which drive the water towards the coast; the two streams produce off the gulf eddies which may affect a sailing vessel, if becalmed.

Beyond Cattaro the general current resumes its course, and off Ragusa is obstructed by the numerous islands to the northward, when it sets chiefly to west-northwest and west

Among the islands, the stream is generally in the direction of their length, or from east to west, and it is more regular in the larger channels than in the others. The rate varies according to the wind and state of the tide, which latter is considerably felt here and on the coast abreast; with southeasterly winds it sometimes reaches 3-1/2 to four miles an hour, especially at the eastern entrances. In the narrow channels it is more rapid and variable, in consequence of the water within them with difficulty finding its level, at flood and ebb, outside the entrances.

In the Narenta channel the current sets to the west, acquiring great strength in easterly winds, and when the waters of the river are swollen; when these winds fall, the stream is observed to advance along [31] the Sabbioncello peninsula, leaving a counter current favorable to the navigation of the channel along the island of Lesina.

In Meleda channel, with the wind blowing hard from southeast, the current runs west-northwest at the rate of three and four miles an hour.

In Curzola and Sabbioncello channels, the westerly set is tolerably regular; but southeast winds accelerate it, particularly in the latter, which then becomes almost impracticable to sailing vessels from the westward.

The current in fine weather follows the general direction of Brazza channel. Irregularities are produced by the offsets of the Narenta and the Cetina, but they are of short duration.

In Solta channel the stream sets round and upon the Zirona islands.

In the small channel of Spalatro, it is variable in force and direction.

Outside the islands of Lagosta and Lissa there is a regular westerly current, but on closing them it becomes uncertain. About Lissa the set is nearly always to the west; with continuous southeasterly winds it runs with great strength, particularly towards the western part of the island, whence it strikes off to the northwest and causes an eddy which renders this passage dangerous. The westerly current, in this part of the Adriatic, is accelerated by the outset from the channels of the various islands.

In light winds and calms, the set to the west is at the rate of about three-quarters of a mile an hour between Pelagosa and St. Andrea islets, but with fresh northwest winds its force proportionately decreases.

Near St. Andrea and Pelagosa islets, the current, particularly in winter, has no regular direction, but produces dangerous eddies; these islets should, therefore, be avoided. After passing Lissa and St. Andrea the current apparently takes its former direction, parallel to the islands and the coast.

About Planka point the current is always rapid and variable, and in southeast winds violent eddies are produced. From this point, and among all the islands to the northwest, the tide is considerably felt, and contributes greatly to the irregularity of the current.

At 10 miles seaward of the islands north of Planka point the general direction is north by west, with a rate decreasing gradually from three-quarters to less than half a mile between Grossa island and cape Promotore, but in a strong bora it entirely ceases.

Off Premuda island a branch of the northwest current flows southwest towards Anchona, and joins the stream along the Italian coast.

Between Planka point and Zuri island the currents resume their regularity and westerly direction, modified only by strong northerly winds and the set of the sea.

[32] The stream runs generally in the direction of the islands between Zuri island and the Quarnero; but in the narrow channels the water is in a state of constant agitation, and the numerous rocks and islets which lie in them destroy all regularity of flow.

In the four passages between Zuri and Zlarina islands, and in the vicinity of Sebenico, the set is almost always in an oblique direction, with a velocity frequently of three and four miles an hour, which demands great attention. Amongst the extensive cluster of islands and rocks southeast of Incoronata island it is rapid.

At the eastern entrance of Mezzo channel and in the vicinity of Tre Sorelle islets the current runs with great strength, regular in fine, but very variable in rough, weather.

In Pasman strait it is liable to great irregularity, caused by the rocks and islets; strong winds give the stream a motion inclining across the eastern entrance of that channel, when it acquires a rate of three to four miles an hour.

In the Zara channel it sets northwestward with some regularity, with a velocity at times reaching three and four miles an hour.

In Quarnero gulf, and the channels of the Dalmatian coast, the currents are irregular, varying in rate and direction according to wind and tide; they are also influenced by the rivers and numerous islands. Gales from the offing throw a large body of water into the channels, where it is pent up till the wind abates, then runs back with rapidity; if, on the contrary, the winds are from the northward for any length of time, the water is driven into the offing, and as soon as the wind moderates returns with force.

In the Great Quarnero channel, with northerly winds, and during the whole continuance of the flood tide, a counter current will be found setting to the northward along Cherso island. In proceeding to Fiume it is, therefore, preferable to keep along that island instead of the Istrian coast until in the Farasina channel. With the same winds the southerly current at times attains a rate of four miles an hour and in a sailing vessel is almost insurmountable.

During a heavy bora a stream sets along the coast of Istria to the southwest, and out of the Quarnero channel at about a mile an hour; it advances more slowly towards Premuda island, where it takes a southwest by south direction; in approaching St. Andrea islet it sets south-southwest and south As the parallel of St. Andrea is approached, the influence of the general southwest current is more and more felt.

Well out in the offing, in the vicinity of Pomo islet, and between the islands of Lissa and Premuda, very irregular streams will be found.

About cape Promontore and the rocks which surround it, the currents [33] are very strong and variable. Under the influence of the bora they set to the west and west-northwest more than a mile an hour, and their effect is felt as far as Pola. Caution is therefore necessary when in the vicinity of this as well as all other projecting points on the eastern coast.

In ordinary weather, beyond cape Promontore and as far as Trieste, the stream sets slowly along the coast of Istria, strongest at Auro point, at the Marmi Grande and shoals in the vicinity of port Orsera and Salvore point, but its breadth does not generally exceed two or three miles. With northwesterly winds there is a strong set towards the Brioni islands.

Between Salvore point and Trieste the current turns towards the B. and is always felt at the latter place, where it sweeps round the bay on its course to the Venetian shore at the rate of about a mile an hour, decreasing in the offing.

In the gulf of Trieste, in fine weather, the currents are regular, and their direction always southerly. At a short distance off the coast of Istria the motion of the waters is in general towards the southwest or the Venetian shores, and is tolerably regular in fine weather; but it is greatly influenced by wind and tide. This irregularity is much more perceptible on the eastern coast than on the western.

During the fine season there is scarcely any current in the middle of the gulf.

About midway between cape Promontore and mount Conero, the set varies between south-southwest and southeast, at a rate generally of one-quarter to half a mile an hour. There is little or no current during the fine season.

The inshore current, from the head of the gulf of Trieste, always sets slowly about west by south, following the various sinuosities of the coast. It is hardly perceptible during calms in summer, and southwest winds, but under the influence of the bora it probably runs about a mile an hour.

The tides which are perceptible on this coast, and the rivers which empty themselves into the sea between the Tagliamento and Maestra point, have the effect of diverting the current from its usual course; the rivers also bring down quantities of mud and sand, which alter the shape and direction of the banks along the coast, and affect the set of the stream. At Venice, in particular, the sea flows rapidly into the channels and harbors of the lagoons; in receding, the streams in strong sea winds give rise to wide and dangerous eddies.

The general direction of the southerly current is never destroyed, though it may be influenced by wind or other causes, and its continuance is proved by the direction and form given to the banks at the entrance of the harbors and the mouths of the rivers.

A proof of the constant southwesterly direction of the currents from [34] the gulf of Trieste to Maestra point, is the uniform deposit of alluvial matter which has been occurring for ages on this seaboard, an effect which could not have been caused by winds or tides. Deep water is found on the coast from Trieste to the mouth of the Isonzo, while the shores southwestward of this, towards the Piave, and at the entrances of the lagoons, are fronted by shoal water over a sandy bottom; even the lagoons have a tendency to fill up, notwithstanding an incessant scour. At the mouth of the lagoons, at Malamocco and at Lido, large accumulations of sand are formed in a triangular shape, with the apex pointing southward. Between Venice and Trieste are the Isonzo, Tagliavento, Livenza, Piave, and other streams; and it is evident that the sand and mud brought down by them are carried southward by a regular and constant current. If, on the contrary, the water flowed at all to the north at the head of the gulf of Trieste, the port, as well as all those on the eastern coast of Istria, would present the same inconvenience.

From the delta of the Po the streams spread out to the eastward, and then bend to the south and southeast; in spring, on the melting of the snow, and after abundant autumnal rains, the action of the freshets is most perceptible.

From Maestra point the current of the western coast of the Adriatic takes its general direction to the southeast As far as Ancona, it is subject to the deflection caused by the offset from the numerous streams and rivers; its rate is never considerable, seldom exceeding a mile an hour, after the great freshets of the Po, when the surface of the sea to a distance of eight or 10 miles in the offing is colored by the mud brought down.

The constant southeasterly set of the waters along the Italian coast of the Adriatic is demonstrated by the immense deposits formed by the Brenta, the Adige, and the Po, which, by their continued accumulation, cause a gradual advance of the shore seaward, and tend to encumber the harbors. Rimino, Fano, Pesaro, Sinigaglia, and Ancona are said to be filling slowly. The old Rimino light-house is now two miles inland.

In the vicinity of Ancona, and principally to the southward of the port, the current deflected by the projection from mount Conera sets to the eastward, frequently at the rate of a mile an hour; but if the wind blows long from northwest to northeast, the rate exceeds two miles an hour, and the stream may then be dangerous to vessels approaching the land for Ancona, as it sets on St. Clemente rocks.

In the neighborhood of Ancona the regular current of the Italian coast acquires its greatest strength.

Between mounts Conero and Gargano head the current continues its [35] course, following the Abruzzo coast; its rate is estimated at a mile an hour in fine weather, but it is more rapid near the shore of mount Gargano.

The coast of mount Gargano causes a portion of the current to branch off to eastward, while the other part sweeps round the head close along shore, and flows across the entrance of the gulf of Manfredonia without entering it.

The harbor of Manfredonia, which dates from 1256, is slowly filling with sand washed up by the sea during southeast gales, but not from the effect of currents.

The branch setting eastward from the coast of mount Gargano flows towards Pianosa and Pelagosa islets, and meeting the western stream already mentioned produces rapid eddies. Around and among the Tremiti group, the easterly current is of great strength.

From Gargano head to Otranto, the inshore stream, having resumed its southeast direction, attains its greatest velocity, which is estimated at 1-1/4 miles between Gargano head and Brindisi, and nearly 1-3/4 miles an hour between the latter and Otranto; with northerly winds this rate rapidly increases, and sometimes exceeds three miles an hour. It is generally weak in summer, especially with on-shore winds, but with those from northwest its strength is sufficient to require attention.

The sand carried by the currents, and proceeding from the rivers Candelaro, Ofanto, and Carapella, is said to have formed the ridge of land which borders Salpi lake. Also, that farther south it is slowly filling the harbors of Barletta, Trani, Bari, and Brindisi more than 100 miles distant.

The current after passing cape Otranto follows the trend of the coast southward, and flows close round cape Sta. Maria di Leuca into the Mediterranean.

The off-shore currents on the Italian coast are variable in their strength and direction according to prevailing winds. The bora winds drive the water towards the Italian, and southwest winds towards the Dalmatian, coast, while southeast winds cause an irregular curve on either side. After a strong wind has lasted two or three days, a current contrary to that previously running will always be found as soon as the wind abates, and will continue until the former has resumed its usual course.

From the great influence of the slightest change of wind on the currents of the Adriatic, it is supposed that they do not extend to any great depth; and, according to some observations, the motion of the stream does not reach beyond four or five fathoms, while from others it is considered to extend to a depth of 11 fathoms.

TIDES

The tides of the Adriatic, like those of the Mediterranean, are [36] very slight and irregular, but an approximate knowledge of the rise of the tide, and of the time of high and low water, may often be of use; and attention should always be paid to the various causes likely to produce irregularities in the tide of any harbor visited. At the mouths of the rivers, especially of the Po, when the waters are swollen by rains or the melting of snow, the rapid outset necessarily retards the floods and accelerates the ebb. The land should therefore be approached with caution at such times, and if necessary the advice of local pilots obtained.

The tidal action is scarcely perceptible at the mouth of the Adriatic; it is first felt at Cattaro on the eastern, and at Brindisi on the western, coast, becoming stronger towards the northern part of the gulf.

On the shores of Dalmatia the tides are weak and irregular; observations show a slight range of tide in calm weather, but none with fresh northwest winds.

In strong southeast winds there is sometimes a rise of one to nearly two feet, and in the channels, and the narrow passages between the islands, a rapid tidal stream of short duration is produced.

The tide stream off the coast of Istria has been found to set against the northeast wind at the rate of nearly a mile an hour, and then return to its southeast course; and at times the effect of the ebb stream has been to cause an apparent stillness of the offing and central waters.

On the western coast the rise varies from one to nearly four feet at springs, according to local circumstances and prevailing winds.

bora gales cause a rise along the coast of Italy; at Barletta, Bari, Monopoli, and Brindisi a tidal action is said to range from a few inches to three feet.

At Venice, with a heavy gale from southeast, the sea sometimes rises six feet above the general level; these gales render the lagoons unapproachable and the channels unsafe; northerly winds cause a fall sufficient to uncover the mud of the lagoons.

A mean of five years' observations at Venice, according to Professor Toaldo, gives a rise and fall of two feet at spring; also the approximate establishments of the ports of Malamocco and Ohiogga 10 h. 30 m., and of that of the port of Venice 11 h. 15 m.

VARIATION OF THE COMPASS

The general direction of the lines of equal variation in the Adriatic and in that portion of the Mediterranean sea contained between the meridians of 10° and 25° east is nearly north and south (true), ranging in amount at the present time, 1880, from 12° in the western part to 7° at the eastern.

The annual decrease at the northern part of the Adriatic sea is nearly 7', and at its southern 6'; near cape Malea or St. Angelo it is about 5'.


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Created: Tuesday, March 22, 2016; Updated: Wednesday, June 22, 2016
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