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 Seanot 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 arepieces 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 widelyit 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 itselfit 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.
Excerpted from Earth by Richard Fortey Copyright © 2005 by Richard Fortey. Excerpted by permission of Knopf, a division of Random House, Inc. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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