Study Area

Study Area

The region to the east and northeast of Akapana was chosen for geophysical study because little was known about this large, open space. Excavations in and around this area provide important clues to what might be lie beneath the surface elsewhere, and provide a baseline for interpretation of geophysical anomalies. The stratigraphy can be simplified into two separate phases. Deeper deposits generally represent earlier period architecture (before about A.D. 800). A gravel layer is encountered above this, which is interpreted to be a pavement that covered earlier architecture, representing a period of urban renewal beginning at roughly A.D. 800 (Couture and Sampeck 2003). The urban renewal included razing the earlier architecture, so it is only found in fragmentary form and it is clear that stones from earlier structures were taken for use in subsequent building (Couture 2002; Couture and Sampeck 2003). Conduits for controlling water flow are commonly found beneath the gravel layer, but are associated with the pavement construction. It has long been established that monumental and residential architecture at Tiwanaku is generally oriented with the cardinal directions (Kolata 2003a), so geophysical anomalies oriented in this way probably represent architecture. In contrast, conduits can be oriented in any direction, allowing us to interpret angled linear geophysical anomalies as conduits. Prior to urban renewal the monumental core was a place of domestic residence, so remnants of these are expected (Couture and Sampeck 2003). Typical residential compounds consist of a large walled enclosure, perhaps 30 m in width (Williams, et al. 2007), which enclose distinct social groups (Kolata 2003b). Wall foundations are often built of parallel courses of stone (often local field stone but sometimes andesite or basalt is included) filled with adobe (Kolata 2003b). Features inside residential compounds are highly variable, but may include residences, cooking areas, and specialized craft areas (Kolata 2003b).

The use of andesite imported from the Lake Titicaca shore up to 90 km away from Tiwanaku (Ponce Sanginés and Mogrovejo Terrazas 1970) presents a somewhat unique and beneficial situation for archaeological geophysics. Rock constructions of all types should be detected by GPR as long as it is within the upper meter, but magnetometry data easily distinguishes between igneous (e.g. andesite) and sedimentary (e.g. sandstone) rocks. Thus, the combination of GPR and magnetometry data allow subsurface architecture to be delineated and the probable rock type identified. Vranich (2006) has shown that andesite is concentrated on the east and west facades of several Tiwanaku monuments, where pilgrims most likely would have passed. In contrast, north and south facing sides were constructed to be less showy and included minimal amounts of andesite. Andesite must have had very important ritual significance because the architects and craftsmen of Tiwanaku went to the shores of Lake Titicaca for its procurement. The presence of Andesite at the site, and fine workmanship would have been impressive and awe-inspiring to the pilgrims.