Geophysical and geochemical survey on the Nazca lines

The Nazca geoglyphs in the stone desert in southern Peru are part of the world cultural heritage. These remarkable drawings have roused the interests of scientists from different disciplines. A joint project of Peruvian and German scientist was launched in 2005 to perform geoscientific studies including geophysical, geochemical, and mineralogical investigations in the desert of Nazca and Palpa. The investigation of shallow structures beneath the Nazca lines aims at a better understanding of the alteration and weathering processes of the desert soils. Suitable geophysical, mineralogical, geochemical, and geotechnical methods should be identified. Our paper reports the application of acombined resistivity and georadar survey at a single test site. The resulting images of the two methods indicate similar structures. Georadar enables a fast and continuous data acquisition but is restricted in its depth of penetration in dependence of the nominal frequency. Despite the dry surface conditions the electrical method yielded good results in the desert area. The resulting resistivity images for both vertical and horizontal slices provide structural information that might be interpreted in terms of lithology and water content. The deepest horizontal slice at a depth of 3.5 m indicates channel structures with lower resistivity. The alignment of these structures is different from the gullies observed on the surface. The lower resistivity might result from higher water content in these channels. Conclusions for a durable conservation of the Nazca lines and areas can only be drawn reliably once the physical and chemical processes at and in the vicinity of the geoglyphs are understood correctly. Our approach tocombine geophysical, mineralogical and geochemical methods proves to be successful to extend the knowledge of these processes.