THE TECTONIC SETTING AND HYDROGEOLOGICAL NATURE OF THE NAZCA LINES

The Nazca lines are a myriad of very old (~70 BCE – 700 CE), large geoglyphs spread over 30,000 acres of the Peruvian pampas that are visible from the air and adjacent mountains. The glyphs have spiral, zigzag, trapezoidal, and quadrangular form including large rectangular fields cut into pediment alluvium atop a plateau between 400 to 500 m elevation along the southern bank of Rio Ingenio, a major tributary of the central Andes Rio Grande drainage. Surface alluvium weathers to a dark desert varnish that lends stark contrast to disturbed, lighter substrate giving form to the glyphs. This marginal-marine setting receives less than 1-inch of rain per year so that disturbed ground remains preserved. The lines likely originated from human augmentation of natural hydrogeological conditions to divert spring water flow from bordering mountains into irrigated fields sitting atop a tectonic bench having gently tilted bedrock forming a structural funnel. Seasonal runoff naturally flows downhill to this area where agricultural systems evolved from early paddies with zoomorphic and phytomorphic forms into subsequent, expansive fields with trenched irrigation. The porous, unconsolidated, surficial materials of the Nazca aquifer get periodically recharged from seasonal mountain runoff to discharge freshwater gradually along the plateau edge where the springs were first discovered, then engineered into sophisticated water-supply systems as cultural centers arose. The Nazca lines were developed to take advantage of natural hydraulic conditions reflecting a unique structural setting where a thick ridge of oceanic crust (Nazca ridge) is being subducted beneath the South American margin at a speed of ~1 cm per year. The battering-ram effect arches overriding continental crust upward into a structural culmination where the oldest bedrock is unroofed along the convergent-plate boundary. The map geometry of the Rio Grande drainage resembles a candelabra with a seaward base from where deeply rooted faults propagate landward and flower upward into normal faults atop the culmination. Prior archaeological work and published geological data are augmented with a remotely sensed structural hydrogeological framework to exemplify how the Nazca aquifer was utilized over time. The framework was built and rendered using Google Earth, QGIS, SketchUp Pro, and a 3-point structural-plane solver programmed for use with NASA's WorldWind virtual Earth globe. By identifying the hydrogeological nature of the lines, more recent 'counterfeit' ones can be discerned.