Adios

We have finally reached the end of reviewing the main theories for the Classic Maya collapse! Admittedly, before I got reading in depth, I was always biased towards the drought hypothesis as it seemed like a convenient explanation for such a societal and political change. I initially believed that drought triggered a chain of destructive events beginning with crop failure that eventually led to the demise of an already out-of-balance cultural system. The series of severe droughts most likely placed a great deal of stress on the elites, in turn affecting their systems and leading them to fight over tributary domains, as food and water resources continued to diminish with the advent of a natural disaster. Socio-political upheaval combined with environmental degradation that may have resulted from deforestation in the face of a hungry population ultimately led to a crumbling society.

However after reviewing all this in further detail, I now believe that they did not overshoot the carrying capacity, and while there may have been deforestation (some of which was necessary in order to build the large cities and construct magnificent monuments), with some areas more deforested than others, I do not think that this could have been a factor leading towards their collapse (McNeil, 2011). The evidence towards a severe drying trend is unequivocal, yet it did not seem to affect all sites. The drought theory still remains controversial among many archaeologists who advocate a blend of overpopulation, a weak economic base, and an internecine struggle for control among the elites, with a subsequent dramatic fragmentation of political power, as the main factors for causing the collapse (Aimers, 2011). McAnany and Negron also reject the drought hypothesis as the ‘prime mover’ of societal change.

After speaking to Dr Elizabeth Graham, an archaeologist and lecturer here at UCL, I think that economic change had a great role to play in the collapse. A bad economy can ruin a society, even today. We have seen that drought affected the Aztecs and Toltecs too, but their demise was ultimately attributed to other factors. If they were able to deal with the drought conditions, surely the Maya, who were the first complex Mesoamerican civilisation to exist were perfectly able to do so too, just as many societies can today. Yet in times of economic stress, divine rulers would not have been as resilient to a drought, adding to the socio-political problems.

 Economic change could also potentially explain the differential abandonment of dynastic centres that lasted over 125 years. As population declined in the south, the north experienced a large influx of population- at least temporarily. The first major dynasties to dissolve were those that ruled over landlocked centres like Calakmul. Those located strategically near the coast and major waterways such as Tulum (on the Caribbean coast of modern-day Mexico) continued to flourish well into the Postclassic period. Perhaps the coastal populations were the last to collapse because they were near to trading ports, and because they had more accessible water resources, unlike Copan and Calakmul that sat astride permanent water sources, which were highly dependent on rainfall. This leads me on to my final point. Did the end of the divine rulership actually qualify as an apocalyptic collapse, as identified by some movie producers (e.g. Mel Gibson) and writers (e.g. Jared Diamond), or did the so-called ‘failed’ civilisation just transform? After all, there are still 7 million descendants inhabiting the Yucatan peninsula today. 

 A prime example is Mel Gibson who produced the movie ‘Apocalypto’, in which he depicted the Maya in an unflattering manner. While it received good reviews, it was an extremely inaccurate portrayal of the rulers and priests as blood-thirsty savages (I have learnt this only after post 9!!). So if you do end up watching it, do not take it too seriously!

Nevertheless, that is another matter. We cannot ignore the fact that the civilisation was reduced to a mere 3% of its original size and the role of climate change as a destabilising factor should not be dismissed. Climate has long played a role in the rise and fall of many civilisations, including the disappearance of the Anasazi people of the American Southwest between ~1275 and 1300, as well that of the Akkadian Empire in Mesopotamia some 4,200 years ago, and the Mochica culture in Peru around 1,500 years ago, to name but a few (American Scientist, 2005). All these societal collapses have been attributed to droughts, evidenced by the increasingly precise high-resolution records of palaeo-climate.


You may be wondering how this is relevant for us today. Well, owing to the complexity of the climate system and consequently the significant uncertainties in our knowledge of climate change, one of the many challenges facing climate scientists and policy makers is predicting future impacts. Given current circumstances of global warming, it is of real interest to contemporary societies to understand how they can overcome the uncertainty in climate change in the coming years, using the past as a guide toward a better future. Ultimately, we are more interested in what changes will occur and how these changes will translate into impacts that matter to humans. There is already enough evidence that many of the potential impacts of global environmental change carry severe risks that can even be catastrophic. Yet knowing how ancient cultures responded to such changes may give us valuable lessons that can help improve humanity's future responses and policy-making. One thing we can learn from the Maya collapse, in particular, is the importance of water conservation and efficient management. Applying such principals of decision analysis to elements of current understanding and using models of virtual reality therefore seems like the most viable option to try and mitigate risks of climate change as soon as possible, to avoid the same fate as the Maya and other great cultures in human history. 

On a concluding note, I would like to thank you all for reading my blog! I have thoroughly enjoyed my time here on the blogosphere. I would also be greatly interested to hear your views on what caused the Classic Maya 'collapse', so feel free to comment! Adios for now amigos. 

References:

McAnany, P.A. and T.G. Negron (2010) 'Bellicose rulers and climatological peril?' In: McAnany, P.A. and N. Yoffee (eds) Questioning Collapse, Cambridge: Cambridge University Press, 142-175

Last but not least

In the next post I will be concluding the blog, after having exhausted the literature and attempting to gain both sides of the story for each theory, so to speak. If you look in the right-hand sidebar I have added a list of the theories I have discussed (although many of these are interlinked, for example agricultural failure and deforestation or agricultural failure, disease and diets). Hopefully this will simplify things and remind you of what has been mentioned over the past couple of months, so you too can come up with your own conclusions! 

Tree-mendously accurate?

This post may seem rather contradictory after the last couple, but I found a very recent paper that actually gives very robust evidence for drought, with the location and dating accuracy in check. Stahle et al. (2011) have discovered two Montezuma baldcypress trees in Mexico (Barranca de Amealco, Queretaro and Los Peroles, San Luis Potosi) that provide millennium-long, annually-resolved palaeoclimatic records (the first exactly dated records for Mesoamerica might I add). Not only do they reconstruct past rainfall, but they can also be used to date archaeological sites to a highly accurate level, especially in comparison to the proxies such as speleothems and sediment cores that have been constrained by age estimates.

The Queretaro record shows that the most severe drought of the past 1,200 years occurred between AD 897 and AD 922, which extended into the central Mexican highlands. Both records confirm the Terminal Classic series of droughts (Figure 1), indicating that they were centred at AD 810 and 860 – the same as the dates given by the Cariaco Basin core.  I have drawn up a table (below) showing all the key dates for severe dry periods (provided by the studies mentioned in this blog) to see how they all compare with this new reconstruction and to make it less confusing:

Location of proxy	Proxy used	Peak drought conditions
Queretaro and San Luis   Potosi, Mexico	Tree rings	AD 810, 860, 897-922
Macal Chasm cave, western Belize	Speleothem (luminescence, colour, δ18O and δ13C)	AD 754-798, 871 and 893-922
Lake Chichancanab, Yucatan, Mexico	Lake sediments (δ18O, δ13C and gypsum/calcite ratios)	AD 922
Cariaco Basin, northern Venezuelan coast	Laminated marine sediments (titanium content)	AD 810, 860 and 910

Did drought affect other cultures?

I know at the beginning I said I would briefly look at the other Mesoamerican cultures, but there has been so much on the Maya I haven’t had a chance yet. This paper actually documents the rise and fall of other civilisations throughout Mesoamerica including the Aztecs and Toltecs. So...did drought affect them? Before I answer this question, have a look at the map below to see what parts of Mesoamerica they inhabited:

Map of Mesoamerica showing the areas dominated by the Maya, Toltec and Aztec
Source: http://www.erin.utoronto.ca/~w3env100y/env/ENV100/hum/map.htm

Toltecs

The Toltecs dominated central Mexico during the early Post-Classic era; since they lived in the highlands where freezing conditions in the autumn shortened the growing season, early growing season drought would have affected them severely. The tree-ring reconstruction shows that a 19-year drought prevailed from AD 1149 to 1167, which may have easily caused famine. There is a possibility that drought played a role in their demise by pushing the Chichimeca population to migrate to the Toltec state, causing instability and eventual abandonment.

Aztecs

The collapse of the Aztecs is less complex than that of the Maya, as much of the population was decimated with the arrival of the Spanish in 1521, who used weapons unfamiliar to them and introduced new diseases and infections that they were not immune to. A drought during the Colonial era may have also contributed to the dramatic depopulation, weakening their society and making them more vulnerable. The new reconstruction indicates that it was the worst Mesoamerican drought since AD 771, lasting from 1378-1404 (as you can see in figure 1); despite this their collapse has ultimately been attributed to the Spanish conquest (McAnany and Negron, 2010). 


References:

McAnany, P.A. and T.G. Negron (2010) 'Bellicose rulers and climatological peril?' In: McAnany, P.A. and N. Yoffee (eds) Questioning Collapse, Cambridge: Cambridge University Press, 142-175

Explosive Eruption?

As we reach the end of the quest to find the cause of the collapse, I came across this blog post that posted an article by Richard Thornton, who talks about a study that places the blame on superheated volcanic gases and ash. Naturally I researched this further, but could not find the article mentioned. I did however find a similar article on the said Palenque Hydro-Archaeological Project. It is essentially a study of Palenque (as you may have guessed from the project name) – a large Maya city and the background of the blog- that has just been completed after 5 years, by the Foundation for the Advancement of Mesoamerican Studies (FAMSI). Located on the edge of the Chiapas Highlands, Palenque had a plentiful water supply, enabling it to become one of the most sophisticated and prosperous cities of the Maya region, yet inexplicably, it was one of the first to collapse. Palaeo-climate data provide very little evidence of a severe dry period that may have caused the abandonment of Palenque. Instead, a heavy layer of tephra (volcanic ash) dated for around 800 AD was found, along with evidence of destruction attributable to high heat.

Volcanic eruptions most certainly have the potential to ruin a society, causing massive causalities and property damage. The very recent awakening of the Popocatépetl volcano, near Mexico City, which prompted Richard Thornton to write his article, is a prime example. Several million lives could be lost if the volcano were to erupt, especially since last-minute evacuation of such a large metropolitan area is impossible.

There has been a long history of violent volcanic eruptions in Mexico, including that of Xocoteptl around 930 AD, in what is now northwest Mexico City. In fact, Mexico and the other Mesoamerican countries sit atop one of the most active geological zones in the world, containing numerous active and dormant volcanoes. For example, there is a chain of volcanoes (known to be active for the past two millennia) in the Chiapas state of Mexico and bordering Guatemala:

Location of El Chichon Volcano and surrounding cities.  The dotted line shows  the  areas most affected by the ashfall from the 1982 eruption. Source: Espindola et al. (2000)

The 1982 El Chichon volcanic eruption in this region was the worst known one in Mexico’s history, displacing over 20,000 people and causing at least 2,000 fatalities. This was partly due to the fact that people were not anticipating it, and so there was little time to escape once it had begun, and also because prior to the eruption it was not considered a hazardous volcano (De la Cruz-Reyna and Martin Del Pozzo, 2009). 

Before 1982: aerial photo of the summit of El Chichon volcano, Mexico

Post-1982 eruption: a kilometer-wide crater was formed, replacing the summit during the  most violent eruption in Mexico (known to humans) that killed 2,000 people and wiped out 9 villages.
Source: http://www.agiweb.org/geotimes/nov07/article.html?id=feature_danger.html

Espindola et al. (2000) suggested that such catastrophic eruptions may have been the prime mover of collapse of the Maya civilisation between 830 and 915 AD, after studies of past volcanic activity of El Chichon. They found that there have been at least 11 explosive eruptions in the past 8000 years, occurring around 550, 900, 1250, 1500, 1600, 1900, 2000, 2500, 3100, 3700 and 7700 years BP (note that the dates are rounded average calibrated radiometric age years). The 1250 BP eruption (i.e. centred around 676-788 AD) overlaps with the dates of the collapse of the western lowlands, including Palenque, which is located very close to the volcano (see map above). Had the Maya been unaware of the imminent danger of a volcanic eruption, the impacts would have been even more severe. Additionally, the impacts would not have been restricted to local areas due to the pyroclastic flows (a mix of ash, volcanic gases and lava) that would have reached distant sites, causing respiratory problems and potentially death. 


It seems volcanic eruptions may have been a primary cause for the collapse of Palenque, but I do not think it is possible to extrapolate this to explain the abandonment of the other cities. The small amount of literature on this particular subject is not sufficient enough for me to base a proper conclusion on, but for now I will discard this theory and begin to conclude the blog.  

Drought Doubt

Although the drought theory may be a popular explanation for the Classic Maya collapse, it assumes that the Maya were not able to adapt to such climate changes.  Many archaeologists believe that it fails to explain the complexity of the “collapse” and rightly so. Although there are a multitude of sites showing the occurrence of devastating droughts, many sites do not actually show this (see map below), in particular Laminai and other sites along the eastern Caribbean strip in Belize (Aimers, 2011).

Map showing sites with (in pink) and without (in blue) evidence of drought.
Source: Metcalfe (unpublished), provided by Dr. Elizabeth Graham, an archaeologist at UCL

It is therefore important to note that the palaeoclimate data that has been presented needs to be interpreted with care, keeping in mind that they are not always unambiguous. The location, chronology and the proxy used for past rainfall are all important when evaluating various records. For instance, the greater the distance from the area of interest (the Maya region), the less representative the archive will be – pretty self explanatory. So in the case of the Venezuelan marine sediment core record, does it actually inform us of what the climate was like some 2,700 kilometres away in the Maya lowlands? Figure 2 shows us how far away it really is.

Archaeological evidence from the sites marked in blue imply different rates of abandonment at different places. For example, in the Petexbatun region collapse occured in the 8th century, for Chichen Itza in the 11th century and for Mopan Valley possibly as late as the 13th century. Other sites like Laminai were not abandoned until the 1600s (after the Spanish invasion).
The sites marked in red have provided drought evidence, each with different (although still fairly similar) timings of occurrence. This contributes to the doubt surrounding the drought theory. 

Another important point to consider is how well the record is dated. Of course it will never be 100% accurate or precise, as there are numerous problems attached with all types of dating, but there are still some proxies that are far more accurate than others, especially tree rings. Other problems arise from calibrating a proxy and rainfall; we cannot always rely on it to be correct.

While there is enough robust evidence showing that a series of drought did occur, much remains to be understood. The difficulty in comparing palaeoclimate and archaeological records does not help matters and will require mutual cooperation from both fields in order to fill in the large gaps in our knowledge (Hodell, 2011). 

T minus 366 days

Just thought I would let you all know that according to the Mayan calendars we have exactly one year (366 days to be precise as 2012 is a leap year) to live before the world ends...

Deforestation Dispute

The last post advocates the theory of deforestation as a contributor towards collapse and a potential cause of the droughts. However (there is always a however) the hypothesis has been disputed by many who have observed present-day sustainable farming practices by the modern Maya, resisting the idea that the Classic Maya would have done things differently and willingly wreaked havoc on the land. If you cast your minds back to post 4, you may think this is very contradictory considering I commented on the fact that these sustainable methods were not utilised across the Maya region and only at a few sites, but recent evidence by McNeil (2011) has made me think otherwise...

Since the mid-1980s the archaeological site of Copan, Honduras, has been held up as the ‘type site’ for the deforestation hypothesis. It has regularly been used to exemplify how human ignorance of environmental limits  can destroy a city and has been used as a warning for modern populations, in particular by Diamond (2005).

However, recent analysis of pollen in a sediment core taken from the same pond as a previous study that suggested major deforestation occurred, does not support this (Figure 1). Indeed the 3000-year old record does show two periods of heightened deforestation during the Middle Preclassic and the Late Preclassic/Early Classic period (when the Maya began to construct their magnificent cities). Yet surprisingly, the landscape near the city centre was MORE forested during the Late Classic period than the Early Classic, contrasting to many predictions.  

Graph of pollen percentages from the sediment core from Petapilla Pond. 

Interpreting the diagram:

An abundance of the microscopic charcoal and the presence of Zea species of pollen imply that the deforested landscape is a product of human clearance and agriculture and not a product of natural grasslands. During the most dramatic level of deforestation (occurring at 512 cm into the core), 89% of the pollen record is composed of herb pollen that is indicative of human disturbance.

At the second peak of deforestation, coyol palm (acromcomia aculeate), a plant new to the pollen profile, is shown to increase in abundance, likely reflecting agroforestry practices.  

In contrast, during the Late Classic (shown between 270.5 and 250.5 cm) the pollen sequence indicates rapid RE-forestation where terrestrial arboreal pollen increases in composition from 59.8% to 89.8%. Herb pollen is actually much less than expected, especially in comparison to the biggest peak of deforestation.

The decline in herb pollen doesn’t support the environmental degradation hypothesis either; similar patterns have also been found in other pollen profiles from Lake Tamarindito and Coba, both of which were heavily populated during the Classic period. In fact there is ample evidence of how the Maya took care of the surrounding land, creating terraces to reduce erosion, wetlands to maximise their use of land and water along with raised fields and dams. Despite this, it is still widely believed that the Maya devastated their environment.

As you can see, there is great controversy surrounding the deforestation hypothesis, much like Easter Island (see Jenny’s blog for more information)!

Just to add...an interesting hypothesis is that the series of droughts may have actually led to re-forestation as populations starved and migrated elsewhere in search of water and food, allowing the forest to recover. OR perhaps this new evidence actually contributes to the mosaic pattern of collapse, where some cities were not deforested as much as others. Who knows?