Ministerio de Educación
The origin of islands

  • A los lectores
  • A los profesores


    On contemplating the great geological feats carried out by the crashing of the waves against the coastlines in different parts of the world, wise men have often wondered what role the sea plays in the formation of islands. Among land scattered across the surface of the ocean, some arrayed in groups or series, others solitary, it is difficult to tell those separated from the continents by the sea from those which have always existed as worlds apart. Is it possible, considering the present state of science, to try and classify islands according to their origin? Yes. Such a task can be undertaken.

    With the help of the latest resources that botany and zoology have to offer to physical geography, it is reasonable to state that sooner or later we will be able to determine with certainty the way in which each of the oceanic lands was formed and how old they are approximately.

    It is obvious, therefore, that islands, islets and rocky reefs which are close to the coast should be natural quarters of the continent which they are part of geologically. At the foot of high mountains which project advanced capes into the sea, resembling the roots of a holm oak, it is possible to see the crest of lateral links spreading in several places across the surface of the ocean. The profile of continental heights is gradually worn down; mountains are succeeded by hills and then by rocky promontories whose roughness is submerged under the layer of water. An insignificant strait, a simple inlet where the waves meet, separates the cape from a less elevated island, but further away the wide canal opens up and the summit which sticks out of the surface across the submarine valleys is nothing but a rock needle. Beyond lies the open sea, where the submerged reefs, if any, are only given away by the whitewashing foam.

    On all rough coasts, there are plenty of those islets which belong to the primitive architecture of the continent, and in certain spots they form real archipelagos. Norway, western Scotland, the Chilean Patagonia and all the regions where the fjords turn the coastline into an immense labyrinth are bordered with countless islands which also have their inlets, their straits and their islet belts. Indeed, since the not so distant disappearance of the icefields which used to fill all the space between cirques of the snowed plateaus and the outer promontories, the primitive relief has suffered little change; the land alluviums brought about by the torrents have watered very few valleys, and the bases of islands and capes, submerged deep down into the waters, have not been able to serve as a support to sea alluviums, similar to those which spread along shallow coasts.

    The isolated rocks (surrounded by ice in days gone by, just as the garden of Mont Blanc is today) rise now above the waters; but it’s not for that reason that they are no longer ridges of the continental relief; in more shallow waters, where the action of sea alluviums might have had a greater influence, they would have long been connected to the shore.

    Among the islands which have to be considered as simple quarters of the great neighbouring lands, we should also mention, not only those which have been raised by sea or river alluviums – simple prominent banks which are usually found along shallow coasts and near river mouths –, but also the islands which are due either to the gradual rising or to the gradual sinking of the bottom of the ground. For instance, the series of island sandbanks/dunes that protect the coastline of Vrisia and Holland against the attacks of the North Sea, from Wangeroogc to the Texel, is surely the remains of the old coastline and signals – far better than the half-sunk coasts of the Dollart and Zuiderzee – the true divide between sea and land.

    Due to the opposite phenomenon, the coasts of Scandinavia, which slowly rise above the waves, have been enriched by the new islands during the current geological age. In the labyrinth of the Norwegian fjords, on the Lofodcn Isles, in the Cuarken archipelago, some hidden reefs have first become visible as rocks and then as vast islands where land vegetation has replaced algae. While the continent was reclaiming land from the sea, every now and then little islets would rise, spreading across the water like leaves of a gigantic plant. Island rocks rise slowly from the bottom of the ocean, lifted by the same force that affects the neighbouring continent. This phenomenon has not only been witnessed on the coasts of Scandinavia. Perhaps the big island of Anticosti, which stretches over 200 Kms in the Gulf of St. Lawrence, is one of those lands which have risen slowly, because – according to Yule Hind’s statement – no snakes or batrachians can be found in the granite valleys of its hills, unlike on the coasts of Labrador and Canada. Should this be so, we cannot assume that Anticosti has ever been connected to the American continent; it must have risen from the water, in the same way as the islets on the Scandinavian coasts.

    Something quite different happened to Great Britain and most of the islands near the outline of continental masses. It is certain that England was once part of Europe. This is proven by the perfect match between the shores on each side of the Strait of Calais; we also find evidence for this in the flora and fauna on the bigger British Isle, whose animals and flowers are the settlers of a nearby world. Not one single species truly is the result of the spontaneous production of the soil of old Albion. Ireland separated from England in the same way during the current geological age, and around the two main islands we can also find numerous isolated secondary fragments, such as Wight, Anglesey and the Sorlings.

    Many islands situated like England and Ireland, near the continents, are also the waste that the waves, maybe helped by the gradual sinking of the ground, have separated from the shores of firm land. The magnificent archipelago of the Sonda, the Molucas and the islands close to Australia represent the most remarkable example of this division of continental masses. A channel, 30 metres wide and 200 metres deep, stretches between the two big islands of Borneo and Celebes and, reaching further southward, it separates the two volcanic lands – very close to each other – of Bali and Lombock. This channel is the old strait that used to serve as the common border between the continents of Asia and Australia. To the west, Java, Borneo, Sumatra, the Malay peninsula and the Cambodge rest on a submarine plateau which stretches at only 60 metres below sea level. To the east, Sumbava, Flores, Timor, the Molucas, New Guinea and Australia also lie on a sort of pedestal which has been sinking and upon which zoophytes build large reef barriers. As naturalist Wallace’s research in the Indian archipelago reveals, all animal and plant species are completely different on each side of this separating channel; the flora and fauna are Asian in the west, and in the east they are of Australian kind. Even the birds – for which a strait a few miles wide does not represent a big obstacle – are completely different on each group of islands.

    We are, therefore, bound to see on the Australian archipelagos the remains of a big continental mass which shattered in numerous fragments in a more or less remote time. The same could be said of the islands in the Aegean Sea, in Denmark, in the polar archipelago of the New World, of the labyrinth of the Magellan isles and of most of the lands surrounded by shallow waters near the shores.

    With regard to the big Mediterranean islands – Cyprus, Crete, Sicily, Sardinia, Corsica and the Balearic Islands – they too must be the remains of vaster regions connected to such parts of the world as today’s Asia, Europe and Africa. For, even though these lands – except for Sicily – all rose from the bottom of abysses whose average depth is between one and two thousand metres, the fossil and the living species on the Mediterranean islands do not differ from those in the neighbouring continents and therein lies their origin. From a geological point of view, we could say that the lands on the western shores of the Mediterranean basin – Spain, Provence, Italy, Tunisia, Algeria and Morocco – together with the nearby islands make up a more distinctly determined set than Central Europe from Gibraltar to the Caspian shores. Despite the abysses in between them, each of the coasts situated on both sides of the Tyrrhenian has kept a similar physiognomy as regards soil, flora and fauna.



    The Mediterranean islands could also be considered either as quarters of the nearby continents, or as remains of old land partially swallowed by the sea. In any case, there are island masses in the middle of the sea which geologists can only recognise as witnesses of continental spaces which disappeared. Madagascar, for instance, though very close to Africa, seems to be a sort of peculiar world with its own flora and fauna and whole animal families – especially monkeys and snakes – which have more representatives on the planet. How strange! The island of Ceylon, half united to the Hindustan through the reefs, islets and sandbanks in the Rama Bridge, also differs a lot from the neighbouring peninsula in the overall physiognomy of its animals and plants; and instead of being a simple quarter of Asia, maybe it is the remnant of some old continent which used to spread across the Indic Ocean, comprising Madagascar, the Seychelles and some other islands, now almost imperceptible on the map.

    Among the fragments of worlds now disappeared, we also have to mention most of the Antilles and New Zealand. The greater Antilles represent along with the lands of North America a more remarkable contrast than that between Ceylon and the Ganges peninsula. Taking into account the relief and nature of their geological foundations, Haiti and Jamaica do not resemble the low lands of the American shores on the other side of the gulf; their animal and plant species remarkably differ from those on the neighbouring continent, despite the fact that winds, currents, migratory birds and human beings have been contributing for many centuries to bring animals and plants from one coast to the other. As far as New Zealand is concerned, this is a radically different world whose flora and fauna have an essentially original character; neither its fossil species nor its living ones resemble those found in Australia or South America. And so, most scholars seem to support Hochstetter’s view, who sees in New Zealand and on Norfolk island the fragments of a continent isolated since the oldest geological age. Just as Great Britain can be considered as a group of islands hardly separated from its neighbouring continent, its beautiful colony in the antipodes represents an old world gradually reduced to a simple group of islands by the erosion of the sea and some sinking activity.

    The present shape of the islands sometimes enables us to recognise what they used to look like when they occupied a much bigger space. From their relief and ramifications, mountain ridges show their original configuration in a general kind of way; they are like fragments of a skeleton around which imagination can build up the shape of the old continental body.

    Besides, many of these islands – of which we have no more than their primitive bones left and whose plains have disappeared – are cut out in the most peculiar way and their shores present capricious sinuosities. For instance, Choa Canzuni, in the Comoros archipelago, is a set of two solid islands connected by a sort of pedicle; Nosi Mitsiu, in the same spot, seems like a trunk of two broken branches; Celebes and Gilolo, remarkable for the parallelism between their gulfs and promontories, seem to have been built from the same model. And from what we know about the mountains in Borneo, we are inclined to believe that if that big island sank into the sea, the silhouette of its shores would look like those of its two neighbours in the Molucas Sea.

    Beside the fragments of continental masses, old and new, all the reliefs which stick out of the surface of the ocean are islands built by the zoophytes or by volcanoes rejected by the bottom of the sea; this is without exception the origin of prominent lands. We know that some are arranged as ring-shaped reefs, made up of other rings smaller in shape, while the lava cones which rise out at sea boast their hunchback scarp-shaped slopes out of the surface, revealing the independence of their origin with a slope which regularly prolongs itself under the sea. We can see that – as the Stromboli volcano shows/reveals, and even more on the island of Panaria – the waves do not stop washing away the underwater slopes, spreading out the lava and ashes cast by the craters.

    Compared to the lands of continental origin, true islands – made up of lava or built by coral – cover a small area. Taking the general layout of the globe into account, it seems that the separation between the sea and the new emerging spaces must have been much more determined in the earlier stages. On the one hand, lots of ongoing land; on the other, deserted oceans; that must have been the natural distribution, but the incessant activity carried out on our planet – as in all celestial bodies – has altered the shape of continental reliefs and the cavities in between that separate them beyond recognition. In the same way as through rain and snow the sea has scattered lakes over the regions that rise above its level, so have the lands given the ocean thousands of islands and islets which so gracefully change its surface. The river alluviums, the erosive power of the waves, the inner forces that slowly lift or sink vast regions and make lava cones spurt violently, and the countless organisms which put the substances in the sea water to work, all those geological agents have worked jointly to sow islands of different shapes and sizes across the sea, sometimes grouped, others in small groups or totally isolated. Afterwards, the winds, the rain, thunder and other atmospheric meteors, ocean currents, the ebb and flow of the tide, the wave ripples, everything that moves and floats in the water and in the air (birds and fish, algae and wood, foam and dust) have not stopped contributing directly or indirectly to the introduction of life on those islands populated by animal and plant species and, thus, prepare a dwelling for mankind.

    The Oceans. Eliseo Reclús.