Errant stones: the spheres of Moeraki
Sabrina Mugnos

The book Mugnos Sabrina to discover the natural wonders of the world brings us this time (Science and Knowledge No 37). In New Zealand to explore the Moeraki Boulders ...

Taken from Science and Knowledge n. 37 .

We in New Zealand, a slice of Oceania, quell'elusivo continent so remote and exotic as to be almost unbelievable, as unimaginable, even in the times of the early school years. Yeah, because the globe has to wring a good span to show its location, scattered in the immensity of the Pacific Ocean. But its actual distance can be felt only by covering it: from Italy to take the planes - which take turns to mo 'relay at the speed of 900 kilometers per hour - must fly over 25 hours to cover nearly 20,000 miles that need to reach it. Given that the circumference of the Earth only twice. For us Europeans is undoubtedly one half way across the world. Yet, once there, you feel at ease. The inhabitants are hospitable, friendly and serene, the towns are welcoming, clean and equipped with all modern comforts. For the power you'll be spoiled for choice menu of land and sea, through an endless array of ways to cook ethnic food, always good and plentiful. The only small, uncomfortable, at least for us, Mediterranean climate can be. Last year in summer (or in January-February, as we are in the Southern Hemisphere) the temperature was always below 18 degrees, made more rigid by the cold wind and constant characteristic of the island lands. And the sea water is quite cool.
Finally, the same territory is familiar. A luxuriant vegetation covers the surface almost completely, and there are pastures everywhere, pleasantly interrupted by the cultivation of the vine, in the northern South Island, which feeds a renowned wine-making tradition.
It reminds us to be in the immensity of the ocean when it is admired by tens of kilometers long beaches, swept by a mighty wind, full of plants, shells and exotic animals, like seals, elephant seals, penguins and albatrosses.
But the landscape of New Zealand can offer unexpected surprises even him to consecrate the temple's impetuous nature, as majestic volcanoes, some still hyperactive and full of lush hydrothermal activity, massive glaciers and fjords.
In this bizarre scene could not miss a geological extravaganza like the Moeraki boulders (or Moreaki Boulders, in original condition).

As the marbles on the foreshore
This is a group of perfectly round spheres dotting the rocky shoreline of the beach Koekohe, near the small settlement of Moreaki on the coast of Otago, South Island.
Scattered like marbles on the shore, there are over fifty - between intact and crushed. Some are over two meters in diameter and weigh over seven tons, while others come to a few tens of centimeters in size, but on average their diameter is about one meter.

Maori legend has its own explanation of their origin. The group Ngai Tahu, who lived in the area surrounding, the stones associated with the wreck of the Arai Te Uru big canoe, following a storm while sailing southward balls would be the transfiguration of part of its load, or baskets, round food and pumpkins. But other elements of the event have been crystallized in the landscape: the boat would become the reef that extends into the sea up to Shag Point, and the big rock, Hipo, the navigator. And yet many of the hills between Moeraki and Palmerston bear the names of crew members, and the wave that flooded the boat.

Incubated from the sea, arised from the earth
Science, of course, offers another explanation, no less romantic.
At first glance, the rocks seem to have been chiseled and then deposited by the sea, but in reality, their origin must be sought in the opposite direction, or at the mountains that rise behind the beach.
For millions of years, in fact, they have kept the cliffs after they forged in their laps. Then the weather have washed away the softer rock, freeing them and allowing them to roll on shore. It was, in short, a sort of birth.
But their first incubator was just the sea. The process began about 60 million years ago (during the Paleocene), when much of North Otago was covered by the ocean.

Their formation began when small quantities of cementitious material (such as calcium carbonate, silicon dioxide, iron sulphide or iron oxide) dissolved in the water (which remains trapped between the particles sediment during the deposition of sediment on the ocean floor) went to congregate around the organic material present in the sediment deposited on the muddy sea bottom. In practice, objects such as shells, bones and fragments of plants, act as condensation nuclei around which the minerals dissolved in water gradually begin to crystallize. After thousands and millions of years this has led to these gigantic spheres that geologists call concretions.
Finally, about 15 million years ago during the Miocene, the seabed rose up above the sea level, where the erosive forces began their slow work: the rock matrix, ie the former seabed mud, was slowly eaten boulders and saw the light.
Continue reading about Science and No Knowledge. 37 .

Written by Sabrina Mugnos
Geologist, has studied and visited dozens of volcanoes around the world through exploration adventurous and sometimes extreme. It takes many years even archaeoastronomy and astrobiology. His book, The Maya and 2012. Scientific inquiry (Macro Publishing) , is enjoying great success in Italy and in several foreign countries. Involved in courses, seminars and conferences at international, is a frequent guest of television and radio.
For more information: www.sabrinamugnos.com .