The landscape around the Nazca geoglyphs and its history

The subsoil of the geoglyph landscape around Nazca and Palpa is built of (geological spoken) young sediments, which accumulated along the western rim of the Andes and which have their origin ultimately in the erosion of these montains. Here, were the Nasca Plate is pushed under the South America Plate, while the folding of the Andes still continues, many geological disturbances and break lines can be found.  The flatter areas of the pampa desert, now about 500 m over sea level, were originally much deeper, partly for some time below of the sea level. Later on, they arised to different levels. In (geological spoken) youngest time, especially during the Ice Age periods rich of rain, valley systems and erosion channels were formed. So today there are many high plains, which are divided by much deeper valleys and eroded on its rims. Only few of the greater rivers valleys have water all the year. Nowadays, nearly all recognizable erosion channel systems are constantly or nearly constantly dry. So they are relicts from former times richer with rains. – To the east, the spreading of geoglyphs goes into the western foothills of the Andes.

The whole landscape belongs to the areas with the lowest precipitation of the earth and is, except of the oasis-like river valleys, a desert (pampa): a northern branch of the huge Atacama desert extending parallel to the coast. Reasons of the low precipitations are particularly a cold ocean current parallel to the coast, called Humboldt current, which prohibits a wet atlantic climate near the coast rim of the southern part of the west coast of South America. In addition, a mountain ridge between plateau and coast, the so-called coast cordillera, has an offscreening effect. Only when the cold cast current drops out, the so-called El-Niño-accident, it may come to unusual rainfalls (in recent time obviously more abundant). More or less over the whole year there are day tempatures between 20° and 30° C.

So, the few annually wet river valleys are oasises and basis of human life in this region – since about 3500 years, when still much less area was desert. They can only be used enduringly for agriculture only by cleverly devised irrigation systems. Today, cotton plantations are dominating.

By strong winds, the surface of the pampa is blown out in a way, that a cover of remaining smaller and bigger stones prevents from further wind erosion. Correspondingly, in other areas big wandering dunes can be found, so the Cerro Blanco, the highest located wandering dune of the earth. The uppermost stone pavement of the pampa is principally unchanged since thousands or ten thousands years. The longer it is untouched, the more purple brown is it coloured by weathering, while the unweathered subsoil is much lighter. Either this changes by natural erosion (i. e. by water courses) or by human interventions. These may be very old, as the geoglyphs theirselves originated by removing of the uppermost stone pavement, or very recent, as traces of vehicles, buildings, cultivating efforts, grafittis or other soil movements.

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