Introduction A Land of Superlatives Imagine a single mountain chain stretching uninterrupted over the same distance as that from New York to Moscow -- over 4500 miles (7000 km) of rock and ice, smoldering volcanoes and needle-sharp granite spires, buffeted by storms and interspersed with dripping cloud forests and searing deserts. Above its entire length the mightiest bird alive soars on 10-foot (3-m) wings, effortlessly riding the thin, frigid winds 3 miles (5 km) above sea level. Far from a fantasy, this place exists. It is called the Andes of South America, the youngest, longest, most varied mountain range on earth. Here lives the great Andean condor which, though a fraction of the size of its Pleistocene ancestor, is the largest, heaviest flying land bird in the world. Like an enigmatic mountain spirit, it can be seen gliding high over icy crags and abyssal canyons, intelligent and wary, personifying all that is wild and free throughout this ultimate wilderness. Plate Tectonics The Andes are a geologically dynamic mountain chain, still in the full throes of formation. Think of the surface of our planet as a great restless tectonic jigsaw puzzle made up of jagged, jostling plates of earth crust shifting this way and that, a process known as continental drift.

Driven by the deep inner forces of heat convection within the earth''s mantle, some plates separate (such as that forming the Great Rift Valley of East Africa), while others collide (as in the Himalayas), and still others rasp and scrape uneasily past one another (as in California''s San Andreas fault). Where two plates of unequal density converge, the heavy oceanic plate will sink beneath the older and lighter rocks of the continental plate, very often giving rise to violent volcanism as seen in Japan, Russia''s Kamchatka Peninsula and Alaska. Nowhere does a continent and ocean floor plate meet on a vaster scale than the encounter between South America and the eastern Pacific Ocean''s Nazca Plate. Having separated from the great supercontinent Gondwanaland some 200 million years ago, South America drifts steadily westward, whereas the oceanic Nazca Plate is propelled just as inexorably eastward by the undersea volcanism feeding the actively spreading mid-ocean ridge like a gigantic conveyor belt. Where the two meet the basaltic seafloor is forced to take a deep plunge beneath the floating continent, creating what is known as a subduction zone, where the crust is reabsorbed into the earth''s mantle. At a rate of several centimeters (about an inch or two) per year, the two plates thus override one another, grinding and buckling as they go, and rumpling South America''s entire western seaboard into a geologic-scale crumple zone: The Andes. This mountain-building process, which began 70 million years ago, gave rise to the great mountains we see today in just the second half of that period, a mere bat of an eyelid in geologic time-scales. And it is still constant and ongoing, revealing itself in a breathtaking variety of contorted shapes and forms many thousands of feet high.

Seashores are thrust skyward and ancient layers of sediment are folded and rolled upon themselves as if they were dough. In central Peru massive slabs of bedrock are squeezed up into sawtooth cordilleras, growing by several feet with each shuddering earthquake. Far to the south granite spires likewise claw the stormy Patagonian skies. Elsewhere swarms of volcanoes add their stamp to the already tormented ridges and plateaus, more than 200 of them grouped into three separate clusters. These are the products of intense heat released by friction deep within the subduction zone, where the oceanic plate is reabsorbed. Between the upward thrust of the continent and the downward plunge of the seafloor the vertical contour of the mountains is mirrored below the sea where the crust angles down some 25,000 feet (7500 m) into the abyssal Peru-Chile Trench before vanishing beneath the continent. North of the Equator As the condor flies, so the Andes keep changing, for no two areas are similar. From the shores of the Caribbean to Cape Horn, at the doorstep of Antarctica, they slash unbroken through 67 degrees of latitude.

Acting like a great rampart blocking some of the earth''s major wind patterns, the Andes even create some of their own extremes of climate. At the Equator, where intense sunshine glints off small rounded glaciers topping smoldering volcanoes like white woolly hats, the Andes run roughly north-south in two parallel cordilleras that are separated by Ecuador''s fertile, heavily populated central valley at about 9000 feet (2700 m) elevation and 50-100 miles (80-160 km) wide. Further to the north, in Colombia, the volcanoes give way to gentler mountains. Here they swing eastward while forking into three distinct ranges separated by even deeper agricultural valleys. Bathed on either side in moist tropical air from the Pacific Gulf of Panama and the Caribbean Sea respectively, these mountains are rain-drenched throughout, save for dry, sheltered microcimates. At the Colombia-Venezuela border, as if losing their momentum, the easternmost of these three branches divides one last time before petering out. One final hurrah comes with the impressive 18,935-foot (5775-m) massif of the Santa Marta mountains -- Colombia''s highest range -- which stands alone near the Caribbean coast. Southward Through Peru and Boliva From the Equator looking southward, both mountains and climate change radically.

At the Ecuador-Peru border the bold march of the Andes seems to hesitate, momentarily fragmented. With low saddles dropping to about 1500 feet (450 m), this is the closest to a gap in the chain as the Andes experience over virtually their entire length. Making a sudden kink, they then quickly re-form and run fair and straight in a southeasterly direction throughout most of Peru, a backbone laid bare by upthrust, with several parallel ridges rippling a broad, sere plateau known as the puna. Here the western slopes of the Andes herald some of the driest environments on earth, the Sechura and Atacama deserts, starved of moisture even though the Atlantic air flow that saturates the Amazon basin laps their eastern flanks. At the junction with Chile and Bolivia everything changes once more. Here major faults gouge the chain and create some of the deepest canyons in the world, surrounded by snowy volcanoes sputtering ash into the thin mountain air. Like a teeming army these active volcanoes advance in a column for hundreds of miles due south far into Chile, while another, much more tranquil string of mountains, the Cordillera Real, takes an enormous detour eastward through Bolivia. Between the two is encased a vast high-altitude basin known as the Altiplano, bordered by mountains all around and perched more than 2 miles (over 3 km) above sea level.

This bowl once held huge inland seas, which were transformed by a gradually desiccating climate into a series of enormous salt pans, eerie white crystallized expanses stretching as far as the eye can see under the cold glare of the sun. The Chilean Subtropics For the rest of the journey the Andes trace a straight and narrow line southward, barely curling east one last time just as they reach the tip of the continent. In central Chile another dramatic climate reversal takes place where the prevailing South Pacific winds from the west spread a cloak of humidity onto the Andes'' seaward slope. Gradually they are transformed from the parched, snowless volcanoes and geyser fields of the north into the increasingly wet and wild realms of the temperate south. Lakes and waterfalls mold the great Valdivian forest of Chile, which soon gives way to the much cooler fjords and islands of the more extreme latitudes. Here, Southern Ocean tempests in full force unleash their fury, carving the land and feeding the only icecap outside of polar regions. Temperate rainforests of Gondwanaland character envelop the misty slopes. Massive tumbling glaciers slice and wend their way fro.