Ice-Cores, Sediments and Civilisation Collapse: A Cautionary Tale from Lake Titicaca

Article excerpt

Introduction

In 1993, Andean archaeologists began to argue that the great state of Tiwanaku located on the southern shores of Lake Titicaca in today's Bolivian highlands experienced a collapse in the twelfth century caused by a devastating 300 year long drought (Ortloff & Kolata 1993; Kolata 1993, 1996; Binford et al. 1997; Kolata et al. 2000). The argument employed an array of techniques for the determination of the past climate--including glacial ice cores, pollen samples, lake sediment cores and AMS radiocarbon dating. The results have been used to construct an argument which concluded that a massive environmental change had produced the inevitable abandonment of raised field agriculture (Ortloff & Kolata 1993). Without a means of subsistence for Tiwanaku's large urban centre, the authors suggested that civilisation collided with an environmental threshold which could not be resolved by human endeavours (Kolata 1993, 1996).

Studies of environmental constraints and thresholds have always played a role in the fabric of archaeological studies (Redman 1999; Van Buren 2001). From the cataclysmic volcanic eruption of Pompeii to ancient Egyptian droughts to the great Mayan collapse, archaeologists make this association all over the world and throughout time (Fagan 1999). Recent publicity about El Nino, global warming and climate extremes has promoted a popular infatuation with environmental conditions and their impacts on cultures that has led to an increase in academic and secular publications about the subject (for example, see Stanley 1998; Redman 1999; Stevens 1999; Henderson et al. 1999; Keys 2000; Thompson 2000; Van Buren 2001; Fagan 2003).

Today, archaeologists look to modern technological advancements in meteorology and palaeoclimatological research to uphold environmental reconstructions, and this has undoubtedly brought a new generation of archaeologists and palaeoclimatologists together to search for environmental extremes and thresholds. However, this creation of multidisciplinary research teams has also shown up an ambiguity between the disciplines. The interdisciplinary discourse can compromise measured empirical data by conscious and subconscious preconceptions of final interpretive goals. This promotes a circular reasoning between palaeoclimatologists and archaeologists, which ignores the mismatch between environmental and archaeological timescales (Driver & Chapman 1996).

In the Andean case study presented here, scientific inferences and calculations of ice and lake sediment core data have been published four times in the archaeological literature as an 'empirical reality' (Kolata et al. 2000). But a detailed analytical review of the scientific evidence will show that information has been selected to support the drought argument, thus promoting a false empirical reality to the archaeological community. This paper will show that the main problem with interpretation is that palaeoclimatologists and archaeologists have failed to distinguish between the timescales appropriate to environmental and archaeological evidence.

An Andean 'Agrarian' collapse and Tiwanaku history

Tiwanaku is the highest archaeological urban centre in the world. The site is situated approximately 20km south-east of Lake Titicaca along the Rio Tiwanaku in today's Bolivian Altiplano (Kolata 1993). Since the first descriptions by Pedro de Cieza de Leon ([1539] 1969) in the sixteenth century, Tiwanaku has been plagued by myths and legends of environmental collapse. Calancha ([1638] 1939) in the seventeenth century spoke of cataclysmic fire and flood that ravished the landscape and destroyed the culture. Castelnau ([1850-1851] 1939) in the mid-nineteenth century proposed that some cataclysmic event had made the land too harsh for human subsistence. Half a century later, Posnansky (1945) described Tiwanaku as a sophisticated society that was the centre of the New World but underwent collapse resulting from a cataclysmic environmental event that made the Bolivian Altiplano into a cold harsh climate. …