TECTONICS BLOG Rev

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Hydrogeological interpretation of some Nazca Lines along the South Bank of Rio Ingenio

Figure 1. Captured GE display of Nazca lines from a hydrogeological perspective including surface-water-diversion elements, trails and hypsography. The oldest glyphs are located high along the south bank of Rio Ingenio where groundwater seepage naturally occurred because of the hydrogeological framework . The lines are water circuits that divert stream flow downgrade and across the pampas for field irrigation. The oldest glyphs are cross-cut and overprinted by younger water mains and distribution circuits.

South view of the Nazca aquifer along the South Bank
of Rio Ingenio highlighting a modern aqueduct.

Figure 2. The top diagram is a hydrogeological profile of the Nazca aquifer showing surficial and bedrock aquifer components. The middle figure is a captured GE display of the aquifer from an oblique view looking Southeast that shows the perched nature of the Nazca aquifer sitting above active valley farms and a modern aqueduct (bottom GE figure).

The Nazca Lines in Google Earth 2019

Figure 3. Nazca physiography, hydrography, and early geoglyphs as seen on 2019 GE imagery.

'The Oculate Being' with GE image overlay
Figure 4. A renowned anthropomorphic Nazca geoglyph is carved into a hillside above the pampas and has no apparent water-related utility. An internet search for aerial photos of this feature includes one shown below that was added to GE for an enhanced display of its details.

Tectonic setting and the Nazca Impact Craters

Figure 5. Captured GE displays of the suspected Nazca impact crater (~23 Ma) and associated East-Pacific Rise, Nazca Ridge(s), far-field lithospheric welts, tectonics plates, and volcanoes. The oblique impact came in from the ESE and imparted deeply penetrating and widespread fracture systems that helped shape the East Pacific region.

Table 1. Names, geographic coordinates and diameters of two of the larger, suspected craters associated with the Nazca impact event.

Crater      Longitude (dd)   Latitude (dd)   Diameter (km)
Nazca-1     170.817829         19.056199            60
Nazca-2     171.412033         19.828540            80

Regional geological map and cross sections

Figure 6. GE captured views (top and middle) and corresponding regional tectonic profiles (bottom) across the Nazca Ridge and continental margin.

Geological setting and cross sections through
part of the Rio Grande drainage

Figure 7. GE display of U.S. Geological Survey geology theme showing a trace of regional synclinorium, the alluvial blanket hosting the Nazca aquifer, and the Rio Grande fault-system interpretation. Geological cross sections across the depresión de Ica-Nasca (fig. 11) illustrating how bedrock is gently titled by normal faulting atop a structural culmination.

Nazca aquifer surficial and bedrock elements

Figure 8. The Nazca aquifer has both surficial and bedrock components. The bedrock is gently tilted to direct flows downslope to the south bank of Rio Ingenio where thick alluvium occurs. The blue lines are traces of open, synclinal (V) fold axes. Dip/strike values noted on 3D white ellipses.

Nazca Lines structural setting and bedrock stratigraphy of the Tertiary Changuillo Formation

Figure 9. Morpho-structural map and a representative bedrock section from Delle Rose and others (2019) . Note how the depresion de Ica-Nasca is the keel of regional synclinorium.

Nazca 1:100:000 scale stratigraphy

Figure 10. 1:100,000-scale geological mapping includes a stratigraphic column showing the two principle units comprising the Nazca aquifer (Wetzell and Matos, 2003).

The geoglyphs are ‘earth markings’ in the form of shallow trenches or raised berms and mounds with up to 60 cm relief and large areas cleared of soil and stones.

Figure 11. Profile depiction of a Nazca line by Masini and others (2016).

Timeline of some pre-Columbian human-cultural periods, complexes, and traditions with respect to Holocene global temperature

Figure 12.The Nasca culture falls into a time when human social communities and networks were proliferating worldwide but subject to local environmental constraints and global climate change.

Nasca Art temporal and thematic categories

Figure 13. The Nasca art defines early, middle, and late cultural stages depicted first by naturalistic motifs, followed by agrarian and religious ones, and culminating with militaristic themes with many human trophy heads symbolically (?) serving as planters (from Proulx's Nasca iconography and ritual-heads website).

Two GE examples of Nazca geoglyph stages

Figure 14. GE imagery is used to digitize early, localized and naturalistic glyphs that become superimposed by later ones that are part of expansive water-diversion circuits.

Ocean-Drilling Program Site 1236 Coring results

Figure 15. Major climatic and sedimentation changes occur in the stratigraphic record of the Nazca Ridge at
~24 Ma, the suspected age of the Nazca impact crater.

Nazca aquifer model extent (left) and
water-diversion circuits

Figure 16. Geospatial elements and fresh-water flow directions in the Nazca aquifer

Starburst geoglyph hydrology

Figure 17. Ancient water-resource engineering techniques were used to short-circuit shallow-subsurface flow in alluvium to irrigate fields and distribute water through trenched circuits from radial centers.

The original Nazca lines are a myriad of very old (~70 BCE – 700 CE), large geoglyphs spread over 200,000 acres of the Peruvian pampas that are visible from the air and adjacent mountains. The glyphs have spiral, zigzag, trapezoidal, round, and quadrangular forms including large rectangular fields cut into pediment alluvium atop plateaus and alluvial valleys at altitudes ranging between 400 to 1000 m elevation in the Andes Rio Grande drainage. The highest concentration is located along the southern bank of Rio Ingenio, a major, central tributary of the Rio Grande drainage. This marginal-marine continental setting receives less than 1-inch of rain per year so that ground disturbances are preserved. Surface alluvium weathers to a dark desert varnish that lends stark contrast to uncovered, lighter substrate giving form to the glyphs. The lines likely originated from human augmentation of natural hydrogeological conditions to divert seasonal water flowing down mountain streams into irrigated fields sitting atop a perched aquifer with gently tilted bedrock directing hydraulic flows. Seasonal runoff naturally flows downhill to the area having the most glyphs where agricultural systems evolved from early paddies having zoomorphic and phytomorphic forms into subsequent, outlying, expansive fields with trenched irrigation systems. The porous, unconsolidated, surficial materials of the Nazca aquifer get seasonally recharged and gradually discharged remotely along the plateau edges where 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 caused by subduction of the Nazca ridge, a thickened segment of oceanic crust that's being shoved beneath the South American margin at a speed of ~50-60 mm per year. The battering-ram effect arches overriding continental crust upward into a structural culmination where the oldest bedrock is unroofed along the convergent tectonic-plate boundary. The Rio Grande drainage is developed on the eastern flank of this culmination and follows deeply rooted faults that propagate landward and flower upward through the crust to form an array of normal fault blocks stepping down from the culmination crest. 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.

The union of two independent paths of geological research merged one day in 2019 with the result being a discovery of how a unique tectonic setting gave rise to a unique human culture at the dawn of the Common Era. The first path is structural hydrogeological research being conducted on the Nazca lines in central Peru that stems from exploring their nature beginning in 2013 during college laboratory exercises using Google Earth (GE; figs. 1 to 4). The second path is the impact-tectonics work showcased in earlier blog posts that led to the discovery of a suspected, large, Early Miocene (~ 24 Ma) impact-cratering event that set the tectonic stage for the glyph development (fig. 5 and table 1). The bolide-impact fractured and thickened the Pacific lithosphere Eons ago resulting in the Nazca Ridge, and subsequently the East-Pacific oceanic rise (fig. 5). Ensuing, eastward tectonic-plate drift and subduction of the thickened Nazca Ridge is preferentially raising the western continental margin into the Andes Antiplano culmination (fig. 6). The Nazca lines were crafted on the eastern flank of the culmination where down-faulted blocks of gently titled strata are arranged to funnel mountain runoff into a desert aquifer (figs. 7 and 8). The most dense occurrence of geoglyphs are etched into the surface of the Nazca aquifer, a thin alluvial blanket resting on bedrock along the northern edge of the pampas that is cut by the Rio Ingenio (figs. 1 to 3). This work therefore portrays the tectonic setting of the central Andes Mountains of Peru and bordering parts of the Eastern Pacific and the geological components of the aquifer that provided ample freshwater resources to sustain a growing population in a desert environment.

As a final point of introduction, archeologists and anthropologists refer to the culture as 'Nasca', but all geographic names and places as well as geological feature, like the Nazca Ridge, use the consonant "z" rather than "c". So in accordance with my understanding of this dichotomy, I use both versions depending upon whether the subject is animate or not. . .

A thorough, modern treatment of the Nasca culture and their natural resources is provided in a book by Lasaponara and others (2016a) titled "The Ancient Nasca World". This work details over three decades of multidisciplinary Italian research upon which this work principally uses when summarizing cultural traits for geological comparison. Other important works incorporated here include the work of Donald Proulx, Professor of Anthropology Emeritus of the University of Massachusetts that studies the Nasca for decades and maintains a university web site detailing associated aspects.

The Nasca culture stemmed from the Paracas culture, inland wayfarers traveling the Peruvian coast along the foot of the Andean Mountains prior to the Common Era (fig. 5). At this time organized human societies were being established inland in semi-arid lands where river resources provided the freshwater needed to support rural agriculture and the organization of urban cultural hubs with monumental architecture, deity worship, and ritual sacrifice. Much earlier, limited human occupation of the Nasca valley reaches far back as 4000 BCE in spatial association with groundwater springs located at Cahuichi (fig. 3; Della Rose, 2019).

The Nazca lines likely originated from human augmentation of natural hydraulic conditions that diverted spring runoff from bordering mountains into agricultural gardens and fields sitting on a perched aquifer underlying an expansive plateau in an arid coastal setting (figs. 2 and 7). Most of the geoglyphs are probably water trenches, canals, and fields etched into alluvial terraces (fig. 1) draped atop gently tilted bedrock of intermediate igneous and volcanic composition (figs. 9, 10, and 11). Exposed pebbles and cobbles at the top of the alluvial blanket developed a dark, desert varnish after eons of weathering in an arid, marginal-marine setting. The varnish is the oxidized coating of iron-rich mafic rocks that lends stark contrast to unexposed, or in the case of the Nasca lines, thousands-of years old excavated substrate formed of light-colored fine sand to clay (fig. 11) giving visual contrast to the numerous geoglyphs cut into the alluvium over time, and observable from mountain elevations, aerial flights and remote sensing (figs. 3 and 4)

The Nasca architecture, graves, and iconography conveyed on pottery and in textiles are arranged by archeologists into early (proliferous ~70 BCE - 200 CE), middle (transitional ~200-400 CE ), and late (monumental ~400-700 CE) thematic stages (fig. 12). These stylistic, iconic depictions of an antiquated culture only convey so much information, so the cultural significance and meaning of the Nasca lines have been a matter of considerable study, analysis, and debate since the 1940s, with the area being designated a United Nations World Heritage Site in 1994. The lines have been measured and categorized in great detail including their lengths, widths, geometric arrangements, and intriguing zoomorphic (animal), phytomorphic (plant), and anthropogenic forms (figs. 3 and 4). Early archeological work on the lines by Xesspe Mejia in 1942 noted the linear similarity between the glyphs, water channels, and aqueducts that tapped the water table. Many other, similar associations have followed that demonstrate the lines definitive link with water, irrigation, and agriculture. Potsherds litter the terrain and are incorporated into earthen mounds leading researchers like Silverman and Proulx (2002) to associate the lines with water-related ceremonial paths through irrigation networks reflecting social space. A detailed hydrologic study of the Nazca area was conducted by the University of Massachusetts geologists in the 1990s in association with David Johnson (1999). That work also noted the association of the lines with aqueducts and concealed faults that channel groundwater flow.

The Nasca flourished during a time when global climate temperatures were a few degrees Centigrade cooler than now and consistent through a 700-year period before the onset of a series of droughts that preceded a 500-year slide into an anomalously chilly time known as the little ice age (fig. 12). Close scrutiny of geological cores taken from Holocene Andean glaciers and nearby lakes show that dust storms peaked around 600 CE (Thompson and others, 1985) within a 190-year prolonged drought (~540 - 730 CE; Lasaponaro and others, 2015). This climate shift shrank water availability that most likely led to societal fragmentation, collapse, and redefinition. Precipitation levels during the Nasca period were more than now because the riverine oases and river dwellings of current inhabitants are focused in valley floors whereas many abandoned Nasca villages and earthworks extend upslope as much as 200 m. Springs rains that now provide vital resources for current river dwellers must have run harder and longer to charge the paddies, terraces, and ponds crafted at the higher elevations.

Based on prior work, and with augmentation of new geological details here, the sequence of glyph development is congruent with the three societal stages defined by their ceramic and textile iconography (figs. 12 and 13), and the discovery of freshwater springs in the Nazca region subsequently led to ancient water-resource engineering practices that fashioned the landscape as part of the resulting societal footprint. The various landscape elements reflect cultural evolution from early coastal ties that shaped naturalistic motifs through subsequent agrarian and militaristic societal stages concluding with polygonal agricultural fields extended over roughly five times the area of that where the earliest glyphs are focused (figs. 1, 10 and 11). Lasaponaro and others (2016) note the steady advance of the populations up stream in different valleys to tap groundwater reserves in addition to earlier efforts on the pampas focused on harnessing spring runoff from the mountains. It is unclear exactly when the Nasca developed aquifer-management methods, but the demands that water scarcity placed on a burgeoning population must have spurred ingenuity in both the manner in which freshwater was accessed and managed that influenced population volume.

I was introduced to the Nazca lines as a teen in the 1970s from reading von Daniken’s (1969) Chariots of Fire. Because of their unique, curious nature, I decided to use them decades later as a prop for teaching college-level physical geology laboratories designed to learn GE. During this time I began mapping the Nazca regional geology using GE to characterize the tectonic setting by adding published geospatial themes for the area and compiling new ones (figs. 5 to 8). The latter includes a detailed structural analysis of stratigraphic layering in fault blocks (fig. 8)that relied upon a custom geology tool developed at the New Jersey Geological & Water Survey (NJGWS) in 2014. This tool uses NASA's WorldWind virtual Earth globe to pinpoint three places along traces of geological planes seen on bare ground in aerial imagery, then extracts their spatial coordinates from the globes digital-elevation model (DEM) to calculate the 3D plane dip and dip azimuth. Multiple oriented planes are generated within an analysis session and saved as data files that are compatible for input into GE as 3D object models.

The Nazca geoglyphs are visible on the Peruvian coast in GE at 50 km eye altitude and become clearer when viewed even closer to ground surface (figs. 1 to 4, 14 and 16 to 17). This study was conducted by highlighting places and features in GE using vector and raster data in the form of placemarks, polylines, polygons, custom imagery, and embedded symbols with notation. GE is a versatile platform that can be used to place features in a geospatial perspective to facilitate the geological analysis of an area like this and resulting in this hypothesis based-on remotely sensed geospatial information. Nazca geoglyphs on the pampas were constructed with hydrologic, flow-through designs that were developed in a manner that first captured natural seeps, then later incorporate more-widespread water-diversion schemes that directed seasonal runoff into fields and aquifer-recharge portals that promoted freshwater discharge into the campo barridas for prolonged periods afterwards (figs. 14, 16 and 17). Recognition of their hydraulic nature helped decipher their relative timing of development that is primarily based on geological cross-cutting relationships (fig. 14). The evolution and complexity of the glyphs through time represent landforms made by an early, expressionistic, sea-faring culture that subsequently evolved into agrarian and concluding militaristic ones. But other, newer glyphs occur among the ancient ones, and apparent counterfeit ones can be discerned when considering the hydraulic designs having 'open' forms versus 'closed' forms.

The Nazca tectonic plate is currently drifting eastward at less that 70 mm year where it has been colliding with and shoved beneath the western continental margin of South America for at least the past 24 Ma (fig. 5 to 7). The comparatively thicker and less-dense continental crust of the South American plate is lifted by thermal and isostatic effects as the oceanic lithosphere is subducted and assimilated into Earth's upper mantle (fig. 6). Regional directions of plate drift differ slightly between the Nasca and South American plates, with the latter having northerly trends in the continental interior (fig. 5). The Nazca lines are located along the continental margin where the Nazca Ridge is being subducted as part of the Nazca plate. The Nazca Ridge is one of a set of thickened, linear oceanic segments radiating outward from the center of the Nazca Plate from a disrupted region where secondary fracturing and magmatism appear to stem from a bolide-impact event, with a central crater herein named the Nazca crater (fig. 5).

The suspected Nazca impact event was discovered while using GE to examine the regional tectonic setting. This event awaits scholarly confirmation, but appears to have been a shower of bolides or a fragmented, larger one of uncertain composition because of the many circular depressions lying amid a set of linear, ocean-floor fractures along a 390^o heading (fig. 5). This set of fractures compliments others where secondary magmatism has risen and thickened the oceanic crust in a region covering almost one-half million square kilometers relative to undisturbed, or 'normal' oceanic crust (fig. 5). The main crater lying at the center of this strain field is about 85 km in diameter (table 1, fig. 5). The bolide impact heading is assumed to parallel the 390^o fracture set that shows symmetric alignment with ocean-spreading ridges, aseismic ridges, and other structural lineation mapped on the sea floor (fig. 5). The same set of far-field lithospheric welts surrounding this impact center as seen elsewhere including a major lithosphere arch located at about 2900 kilometers radial distance that directly corresponds with major segments of the East Pacific Rise! This agrees with prior observations that impact-tectonic strains can form tectonic-plate boundaries and influence subsequent movements including far-field crustal welting around large craters reaching distances of at least 2900 km (Herman, 2005). Deep-sea core 1237A provides a good indication of the timing of the event, as major sea-level and sedimentation changes occurred in the area at about 24 Ma (fig. 15). The tectonic setting defines the unique geological architecture of this area because it is the only place along the convergent tectonic margin where the thickest and most extensive oceanic ridge in the region is being forcefully inserted beneath the continental margin to raise the Andes Antiplano (fig. 6).

The physiographic expression of the Rio Grande drainage resembles a candelabra with a seaward base that branches symmetrically outward on both sides of the Rio Grande at the depresión de Ica-Nasca (fig. 7). The major tributaries of the Rio Grande probably follow deeply-penetrating fault systems along which surface water preferentially incises. It is difficult to prove this without direct subsurface evidence, but surface drainages normally follow dense fracture systems in general, and are portrayed as such here. Because of the unique tectonic setting of the Rio Grande drainage, strata generally dip toward the central tributaries, thus directing surface and shallow subsurface water downhill to the area where the earliest Nazca lines were first crafted (figs. 7 and 8). The oldest, most naturalistic glyphs are focused high on the southern bank of the Rio Ingenio where natural seeps occurred from the edge of a perched, pampas aquifer, and where the early Nasca first impounded seasonal runoff for growing crops (figs. 1 to 3).

The Nazca aquifer is comprised of Quaternary alluvium draped upon of gently tilted, fractured, faulted, and warped Tertiary and younger bedrock (figs. 7 to 12). The hydrogeological framework therefore has both surficial and bedrock components with bedded strata overprinted by secondary and compound tectonic structures. Detailed stratigraphic aspects of the area are based on prior map and detailed geological studies (Wetzell and Matos, 2003; fig. 10, and Delle Rose and others 2019; fig. 9) but the structural controls on the conceptual aquifer model were derived from using the aforementioned WorldWind virtual-mapping application (fig. 8).

The regional geological cross sections show that the physiographic feature named depresión de Ica-Nasca defines the southwest limit of the Nazca lines because it is the keel of a structural synclinorium between strata dipping seaward off flanking mountains (fig. 9) with a high groundwater-recharge potential as opposed to shoreward strata that dip inland, lack the recharge potential, and is therefore a comparatively poor aquifer. But the Nazca lines rest on the northeast limb of the syncline also because thick alluvial fans emerge from mountain passes that mantle fractured bedrock and become seasonally saturated (fig. 8).

The porous, unconsolidated, surficial materials of the Nazca aquifer therefore get seasonally recharged from the mountain runoff that also infiltrates into underlying fractured bedrock strata of the Tertiary Changuillo Formation (fig. 9). Seepage discharges along the riverbanks and plateau edges occurs from both surficial and fractured bedrock lying directly above modern, active aqueducts (figs. 1 and 2). Bedrock strata are gently tilted in adjacent fault blocks that weather deeply along fault systems that surface-drainage systems follow and and provide aquifer recharge (fig. 8). The Nazca aquifer was likely discovered along the Eastern bank of the Rio Ingenio where natural freshwater springs seeps from a perched aquifer provided a desert oases that was subsequently groomed and managed to feed water into localized gardens and agricultural plots before more expansive, cultivated fields were developed to meet the needs of a growing theocratic society. But the reason that the freshwater resources are located there is because this tectonic setting is unique along the entire length of the South American Andes Mountains. The battering-ram effect from inserting a thickened section of oceanic crust beneath the continental margin results in the overriding crust arching upward into a a structural culmination where the oldest bedrock is exposed at ground surface along the western side of the South American continent (fig. 2). The Rio Grande and tributaries follow emergent, but concealed normal faults that branch upward and landward from deeply rooted faults situated on the eastern flank of the Andes structural culmination (figs. 6 and 7).