The Earth

An Intimate History (Text Only)

Richard Fortey

• Publisher: HarperCollins
• Year: 2010
• ISBN:
  9780007373338
• Topic: Physical Sciences
• Subtopic: Geology & Earth Sciences

This ebook edition does not include illustrations.

‘The Earth is a true delight: full of awe-inspiring details… it blends travel, history, reportage and science to creat an unforgettable picture of our ancient earth.’ Sunday Times

1
Up and Down

It should be difficult to lose a mountain, but it happens all the time around the Bay of Naples. Mount Vesuvius slips in and out of view, sometimes looming, at other times barely visible above the lemon groves. In parts of Naples, all you see are lines of washing draped from the balconies of peeling tenements or hastily-constructed apartment blocks: the mountain has apparently vanished. You can understand how it might be possible to live life in that city only half aware of the volcano on whose slopes your home is constructed, and whose whim might control your continued existence.

As you drive eastwards from the centre of the city the packed streets give way to a chaotic patchwork of anonymous buildings, small factories, and ugly housing on three or four floors. The road traffic is relentless. Yet between the buildings there are tended fields, and shaded greenhouses. In early March the almonds are in flower, delicately pink, and there are washes of bright daffodils beneath the orchard trees; you can see women gathering them for market. In the greenhouses exotic flowers such as canna lilies can be glimpsed, or ranks of potted plants destined for the supermarket trade. Oranges and lemons are everywhere. Even the meanest corner will have one or two citrus trees, fenced in and padlocked against thieves. The lemons hang down heavily, as if they were too great a burden for the thin twigs that carry them. The soil is marvellously rich: with enough water, crops would grow and grow.

This was an abundant garden in Roman times, and it still is, even if crammed between scruffy apartments and scrap metal yards.

Volcanic soil is rich in minerals; it is correspondingly generous to crops. Outside the city, Vesuvius is more of a continuous presence; the ground rises gently towards its brown summit. New buildings cling on to the side of the mountain, even high up among the low trees and broom bushes that clothe its flanks. The buildings are indistinct, however, hidden by a creamy-yellow haze of petrochemical smog spreading outwards from the frantic centre of Naples towards the mountainside. You pass a road sign to Pompeii, but from the road there is little to distinguish this suburb from any other, for all its fame.

When the road rises into the hills that abut the southern margin of the Bay of Naples, the urban sprawl begins to thin out. The orange groves are more orderly, with the trees neatly planted in rows inside cages made of makeshift wooden struts, draped over the top with nets. The slopes become much steeper than on the volcanic flanks – close terraces piled one upon the other, each banked up with a wall of pale limestone blocks. Medium-sized trees with small, grey-green leaves – which appear almost silvery in the afternoon light – cling to the most precipitous terraces. These are olive trees, the definitive Mediterranean survivors, oil-producers and suppliers of piquant fruit. Their deep roots can seek out the narrowest cracks. They relish limestone soils, however poor they are in comparison with volcanic loam. The villages in this part of the bay are as you would expect of regular, tourist Italy, with piazzas and ristorante-pizzerias and youths with slick hairstyles on the lookout for a fast buck. Even this long before the summer season there is opportunity for a smooth operator. You find yourself agreeing to hire a cab for a day for €200 to hug the congested roads, when you could travel faster on the excellent Circumvesuviana railway for a tiny fraction of the price. Somehow, you, the visitor, have become the rich volcanic soil primed to yield a good harvest.

Near the tip of the southern peninsula, Sorrento commands a wonderful prospect of Mount Vesuvius across the entire Bay of Naples. From this steep-sided town, Vesuvius looks almost the perfect, gentle-sided cone. It could be a domestic version of Mount Fuji, the revered volcanic mountain in Japan. It can appear blue, or grey, or occasionally stand revealed in its true brown colours. On clear days Vesuvius is starkly outlined against a bright sky: a dark, heavy, almost oppressive presence. Or on a misty morning its conical summit can rise above a mere sketch or impression of the lower slopes, which are obscured in vapour, as if it were cut off from the world to make a house for the gods alone. At night, ranks of lights along Neapolitan roads twinkle incessantly. Vesuvius is often no more than a dark shape against a paler, but still Prussian blue sky. The lights might persuade you that the mountain was still in the process of eruption, with points of white illumination tracking lava flows running down the hillsides. From Sorrento, you can make of Vesuvius what you will, for within a day it will have remade itself.

The Bay of Naples is where the science of geology started. The description of the eruption of Vesuvius and the destruction of Pompeii in AD 79 by Pliny the Younger is probably the first clear and objective description of a geological phenomenon. No dragons were invoked, no clashes between the Titans and the gods. Pliny provided observation, not speculation. Not quite two millennia later, in 1830, Charles Lyell was to use an illustration of columns from the so-called ‘Temple of Serapis’ at Pozzuoli, north of Naples, as the frontispiece to volume one of the most seminal work in geology – his Principles of Geology. This book influenced the young Charles Darwin more than any other source in his formulation of evolutionary theory: so you could say that the Bay of Naples had its part to play, too, in the most important biological revolution. Everybody who was anybody in the eighteenth and nineteenth centuries visited the bay, and marvelled at its natural and archaeological phenomena. For geology – a latecomer to the pantheon of sciences – the area is the nearest thing to holy ground that there is. If you were going to choose anywhere to retrace the growth in our understanding about how the earth is constructed, what better place to begin? Where else more appropriate to explain first principles? The long intellectual journey that eventually led to plate tectonics started in this bite out of the western shin of Italy’s boot-shaped profile. A voyage around this particular bay is a pilgrimage to the foundations of comprehension about our planet.

Everything about Sorrento is rooted in the geology. The town itself is in a broad valley surrounded by limestone ranges, which flash white bluffs on the hillsides and reach the sea in nearly vertical cliffs – an incitement to dizziness for those brave enough to look straight down from the top. Seen from a distance, the roads that wind up the sides of the hills look like folded tagliatelle. Stacked blocks of the same limestone are used in the walls that underpin the terraces supporting the olive groves. In special places there are springs that spurt out fresh, cool water from underground caverns. These sources are often flanked by niches containing the statue of a saint, or of the Virgin: water is not taken for granted in these parts. There are deep ravines through the limestone hills, probably marking where caves have collapsed. The country backing the Bay of Naples is known as Campania, and the same name, Campanian, is applied to a subdivision of geological time belonging to the Cretaceous period. If you look carefully on some of the weathered surfaces of the limestones you will see the remains of sea-shells that were alive in the age of the dinosaurs. I saw some obvious clams and sea urchins, belonging to extinct species, emerging from the cliffs as if they were on a bas-relief. A palaeontologist can identify the individual fossil species, and use them to calibrate the age of the rocks, since the succession of species is a measure of geological time. The implication is clear enough: in Cretaceous times all these hilly regions were beneath a shallow, warm sea. Limy muds accumulated there as sediments, and entombed the remains of the animals living on the sea-floor. Time and burial hardened the muds into the tough limestones we see today. They are sedimentary rocks, subsequently uplifted to become land; earth movements then tilted them – but this is to anticipate. What one can say is that the character of the limestone hills is a product of an ancient sea.

The massive limestones continue westwards on to the island of Capri, which is a twenty-minute ferry ride from Sorrento and bounds the southern edge of the Bay of Naples. The island rises sheer from the sea, circumscribed by steep limestone cliffs, and your first thought is how could it support the smallest village, let alone a town. The town of Capri lies at the top of a vertiginous funicular railway running from the harbour. The buildings are ancient and quaint, and, naturally enough, built of the local stone. The blocks themselves are often concealed under stucco. There is a fine medieval charterhouse where the pale limestone is put to good effect in columns supporting cloisters. Almost everything else is fabricated of limestone – walls, floors, piazzas. In the bright Mediterranean light there is an overwhelming sense of whiteness; some of the villas glimpsed on the hillside have the appearance of frosted cakes tucked under umbrella pines. Only dark basalt must have been imported from Vesuvius to make the surfaces of the streets: this volcanic rock is less liable to shatter than limestone. It is not difficult to imagine the racket that iron-rimmed wheels made as they clattered over these roughly-matched, large blocks. On the inner side of the island there are truly astonishing vertical limestone cliffs dropping hundreds of metres to the sea. The Roman Emperor Tiberius spent his declining years in a palace on the island, the ruins of which endure. According to the prurient accounts of his chronicler Suetonius, he indulged every kind of sexual perversion in a life of epicene self-gratification. Small boys were favoured. Those who displeased him were liable to be thrown off the monstrous cliffs. There is a subtle undercurrent in the Capresi atmosphere that hints at such darker things. Just offshore there are two enormous and forbidding sea-stacks – masses of limestone isolated from the main cliff by the relentless erosion of the sea. According to Norman Douglas, this was the abode of the Sirens, whose alluring and fatal song Odysseus was able to resist only by being strapped to the mast of his vessel, while his muffled crew rowed onwards to safety. Capri makes you wonder whether an idyllic hilltop haven might eventually also deprave and destroy. One of the grandest villas (now a hotel) overlooking the fearsome cliffs was built by the Krupps dynasty, once the armourers of German ambitions. Unexpectedly, the builder apparently immersed himself in studying the growth of lampreys, a primitive and parasitic fish. On this island there is a seamless continuity with the past – with Hellenic myth and Roman decadence and medieval devotion. The island gardens have seen the ages come and go, perched high upon the hardened sediments of a sea far more ancient than human frailty.

There is something different about the cliffs behind the harbour in the middle of Sorrento. From afar they have a greyish cast, a dull uniformity, lacking all the brilliance of limestone. The streets career downwards towards the sea below the central piazza, following a steep-sided valley. Now you can see the rock in the valley sides. It is brownish, like spiced cake, and displays little obvious structure. Look closely and you see that embedded within it, like dates in a home-bake, there are darker patches. Some are little more than wisps, others are larger – angular pieces of another rock, here nearly black, there umber brown, some including little bubbles. Then you notice that the same rock has been recruited by the local builders to construct the high walls that line the steeply sloping path, comprising blocks a few tens of centimetres across, neatly cut and used like bricks. Clearly, this rock is softer than the rough limestones that bolster the hilly vineyards and terraces. Then you notice that the same stone has been used to construct the older buildings. Down by the port there are shops and cafés painted jolly ochre and sienna, but where the stucco has peeled – or where warehouses have simply been left undecorated – the same rock is revealed as having been used for their construction. Much of the town has grown from the identical rock that forms the steep cliffs backing the harbour.

This rock is called the Campanian Ignimbrite. Its origin was a catastrophe that happened 35,000 years ago: a gigantic volcanic explosion threw out at least 100 cubic kilometres of pumice and ash. The evidence still covers an area of more than 30,000 square kilometres around the Bay of Naples, extending from Roccamonfina in the north to Salerno in the south. The violence of this eruption would make the event that buried Pompeii seem like a small afterthought. An explosion of steam and gluey lava blew out a great hole in the earth at the edge of the Tyrrhenian Sea – not so much a bite out of Italy’s profile as a huge punch. A vast cloud of incandescent material buoyed up with gas flowed like a fiery tidal wave across the limestone terrain. Lumps of volcanic rock were carried along willy-nilly in the mayhem: destruction of vegetation was complete. When the cloud settled, in many places it was hot enough to fuse solid: the wispy remains of volcanic fragments testify to this welding.^* There were almost certainly Palaeolithic human witnesses to this destruction, who must have thought the gods had gone berserk. The legacy of the earth’s ferocity is this apparently mundane rock that looks like cake. The angular fragments of rock within can now be seen for what they are – pieces of a destroyed volcano. It is ironic that this destruction has now been reversed into constructing buildings that are ‘safe as houses’. Naturally, nothing is safe in this uncertain world. Looking down from the limestone hills you can imagine the hot, devastating clouds settling over where limoncello is now brewed and pizzas are spun, dumping down on the low ground as a thick, lethal blanket. These kinds of rocks were deposited from pyroclastic surges. Another eruption about 23,000 years later was marginally less devastating and did not spread so widely – it produced a different deposit known as the Tufo Galliano Napoletano, the Neapolitan yellow tuff. Rather than the colour of cake, it is the colour of Dijon mustard. Once you can recognize it, you spot blocks of it in many walls and buildings around Naples itself – it is almost reminiscent of the ‘London stock’ bricks that make the Georgian parts of the English capital so appealing. It is there in the walls of Roman remains. Most experts believe that the volcanoes that remain to this day in the Campi Flegrei are aligned around the edge of the massive hole, or caldera, left behind as the legacy of this second huge eruption. The Bay of Naples itself hides most of it. It may yet blow again.

It must be appropriate now to visit Mount Vesuvius. It is 1281 metres high – not a great peak, but grand enough. Strictly speaking, only the cone itself should be called Vesuvius: the wider region, including older volcanic remnants, should be called Somma Vesuvius. To reach the mountain, go to Erculaneo station and catch the bus waiting outside in the bustling suburb. The route climbs upwards through improbably narrow streets, and then out into fields planted with almonds and vines. The mountain produces a wine called Lachrymae Christi – the tears of Christ – as evocative a name as you could wish for an indifferent rosso. Now you can see close up the random assortment of houses that were visible only as flashes of light from the other side of the bay. They seem perilously close to the volcanic cone, and unplanned, as if dropped haphazardly from the sky. Higher still, there is dense scrub, and then, looming above you, the cone itself. The bus disgorges its passengers, who must then climb to the summit along a relentless upward trail. You are following in famous footsteps, for the poets Goethe and Shelley were here before you. Nor are you ever alone: the view provides an irresistible photo-opportunity for tourists of all nationalities. The conurbation of Naples stretches away below, as insubstantial as postage stamps pasted on the landscape.

The dominant colour is a warm brown-black. Nobody could pretend that a huge slope of clinker is aesthetically pleasing. The waste of the mountain has a curiously industrial feel, like slag from a smelter; it is easy to understand the classical notion of Vulcan’s forges working away in the earth’s interior. An excellent guide-book by Drs Kilburn and McGuire of University College, London, reveals that these unpromising pieces of debris are scoria and lithic fragments of the March 1944 eruption. Looking down, you can make out the edges of these latest flows in Vesuvius’ long history extending beyond the base of the cone itself, like chocolate sauce sliding off a steamed pudding. By the pathside, there are occasional large boulders that show black crystals the size of a fingernail; these are pyroxene minerals that had time to crystallize out deep within the chamber of liquid rock – or magma – beneath the volcano. Like everything else around, these rocks are igneous in origin: formed in fire, cooled from melt derived from the earth’s depths. The crater itself is the kind of gaping hole that induces despair in those suffering from vertigo: it is 500 metres across, and 300 metres deep. From the far side of the rim path you can just make out the amphitheatre at Pompeii, with the misty blue of the Bay of Naples beyond; it seems entirely plausible that destruction could be meted out at a distance by suitably violent explosions. The crater sides are sheer. Wisps of steam still arise from one side, like smoke from a poorly extinguished cigarette. Looking across the crater, you can readily see that it is made of piled layers of lava metres thick. You can also make out where flowing lava was replaced by explosive pyroclastic deposits, which are crumbly and easily eroded. Here is evidence for the origin of the kind of lethal clouds that wiped out Roman Herculaneum in the AD 79 eruption. The crater is not stable. Listen: there is a continuous tinkling, like ice in a glass, as pebbles fall from the sides into the interior. The volcano is temporarily quiescent, but there are many descriptions of it while awake. Here is a little of what the philosopher Bishop Berkeley had to say about it in 1717:

I saw a vast aperture full of smoke, which hindered me from seeing its depth and figure. I heard within that horrid gulph certain extraordinary sounds, which seemed to proceed from the bowels of the mountain; a sort of murmuring, sighing, dashing sound; and between whiles, a noise like that of thunder or cannon, with a clattering like that of tiles falling from the tops of houses into the streets. Sometimes, as the wind changed, the smoke grew thinner, discovering a very ruddy flame and the circumference of the crater streaked with red and several shades of yellow…

Nowadays, handwritten labels creak in the wind. On the top of the cone you can make out a solar-powered global positioning system. So often in Italy there is this odd mixture of the improvised with the latest technology.

Vesuvius is an irritable mountain. It has been erupting for 25,000 years or so. It will do so again. It is a classic in geological literature because several of its eruptions have been accurately described over two thousand years. It also demonstrates many kinds of different volcanic activity, from sluggish flows that slowly and inexorably eat up landscape and houses, through ash-falls that suffocate, to pyroclastic flows and surges that run faster than a racing car and engulf the plains in heat and terror. It is a vulcanological case-book. After the AD 79 debacle, which killed two thousand people and buried Herculaneum and Pompeii, there was a great eruption that began in the morning of 16 December 1631. Within a day, ash from Naples had reached Istanbul, more than 1000 kilometres distant. This eruption killed almost twice as many people as had died at the time of the Roman Empire. The rich volcanic soil had once more encouraged the growth of a prosperous people, who had spread over vulnerable areas. Massive pyroclastic flows took their toll. So did the engulfing slurries of mud and ash that flow downhill when heavy rains blend with volcanic outpourings. Ironically, the particles thrown up by a major event serve to ‘seed’ rainclouds in the atmosphere; thus in this tragedy the four ancient elements – earth, air, fire, and water – conspired towards a common deadly destruction. Naples itself, however, was spared. There were many subsequent minor eruptions, usually about eleven years apart, all of which avoided it. An eruption is now overdue, and might well be a big one. The latest, 1944, eruption was studied in detail: something like thirty-seven million cubic metres of magma were expelled within a few days in March of that year. Much was released in the form of ash and ‘bombs’, black masses often shaped like horns or twisted loaves. There were several eruptive phases separated by periods of quiescence, when the crater collapsed temporarily to block the throat of the vent. The almond blossoms everywhere shrivelled on the branch. The villages of Massa and San Sebastiano were destroyed by slow-moving lava flows. The Times (of London) correspondent eloquently described the process:

The progress of destruction is almost maddeningly slow. There is nothing about it like the sudden wrath of devastation by bombing. The lava hit the first houses in San Sebastiano at about 2.30 a.m. but by dawn it still had not crossed the main street only 200 yards away, but was nosing its way through the vines and crushing down the small outhouses more slowly than a steam roller…For a while it seemed as if it would engulf the houses as they stood but then, as the weight grew, a crack would appear in the wall. As it slowly widened first one wall would fall out and then the whole house would collapse in a cloud of rubble over which the mass would gradually creep, swallowing up the debris with it…Masses of steam of slightly darker quality rose as cellars full of casks of wine exploded. Over all one heard a steady cracking as the monster consumed hors d’oeuvre of vine stalks, olive trees and piles of faggots stored in backyards…

If it had been a pyroclastic surge, the whole thing would have been over in a second.

A geologist amongst the crowds at Pompeii would probably be there to observe the effects of an ash-fall that destroyed a whole city as much as to wonder at the level of luxury enjoyed by the Roman elite. Nonetheless, the city’s sheer size comes as a surprise. The discouragingly large crowds at the entrance soon disperse, and you are left to pick around at your leisure. Some of the roads allow a clear view of Vesuvius, and it is not so difficult to envisage the huge shower of hot ash that so effectively entombed this wealthy city for the archaeologists: the warning earthquakes, the great b...