Annotated Bibliography for Environmental Geology Seminar

Allison has gone through the data published by Larson and Michaelsen (1990) and determined that their data do not unequivocally say that the population of the Virgin Branch Anasazi changed either so rapidly or so highly in conjunction with the varying amounts of discharge on the Virgin River. Allison points out flaws in L and M’s dating methods (both in terms of ¹⁴C and by using pottery shards) and shows that a simple reassignment of just a few settlements to a different time period can make an "abrupt population change" become no change at all. We think that these two papers (Allison, 1996 and L and M, 1990) read together will make an interesting set of papers to read and discuss.

This paper discusses the abandonment of the Colorado plateau in 1300 AD from a purely cultural standpoint. We thought it was interesting that they are able to explain the abandonment without invoking environmental causes at all (in fact, they refer to some of the papers we’ve included here, and refuted them). Their theory is that other peoples (the Numics) moved into the area and displaced the Anasazi.

This is an incredibly dense paper combining the research of several people. They have looked at the environmental evidence of climate change (such as pollen, arroyo cutting, 14C dating, and tree ring data) and tried to draw correlations between those data and the abandonment of the Colorado Plateau. If we were cruel, we would have had the class read this, because it is one of the most rigorous geologic papers trying to correlate climate to demographic patterns. They have put ALL their data into two incredibly dense and impossible-to-read figures, which is kind of amusing.

This is a compilation of essays/papers regarding the environment and behavior of the Anasazi up to their relatively sudden abandonment of the Colorado Plateau in 1250 AD. The first two essays discuss the science of anthropology in general, and how anthropologists come up with models explaining the inferred behavior of a people. It also talks about how the Anasazi culture had to be so diverse and complex because they were constantly dealing with environmental stress (they lived in an arid and mountainous region where there was a very narrow band of arable land–valleys were too dry and the mountains were too cold) and environmental variability. Why would a large population suddenly leave the San Juan drainage and all move to the areas which are currently still occupied by modern Pueblo Indians? The following essays go on to discuss the environment of the San Juan drainage area, including the alluvial chronology, vegetation (pollen analysis), and dendrochronology. The final essays discuss the Anasazi demographics, the relationship between demographics and cultural change, and Anasazi adaptive strategies. This book contains a huge amount of information, and is one of the more scientifically-rigorous of the ones I’ve read. Unfortunately, there is no good synthesis of all the geologic/ecologic data with respect to what the people were doing back then, because I would have had you read it. Each of the essays are really dense and take some time to plow through–and each are so specialized that on their own they don’t give a complete picture of what was happening in the Southwest back then. But these folks completely believe that the Anasazi moved due to environmental stresses.

Using tree ring data and population estimates for the Virgin Anasazi of southwestern Utah, Larson and Michael have determined that the this community was strongly affected by droughts. They counted the number of rooms in a settlement and estimated the number of people who would typically occupy those rooms–and then figured out a date for that settlement from the type of pottery found in it in order to figure out the demographics of the Virgin River area. They measured tree rings from the area, dated them using dendrochronology, and calibrated them to a long-term, modern discharge record. They compared the demographics to the discharge data and determined that there was a drought from 1000 to 1015 AD that forced people to change some of their agricultural practices and encouraged them to build up stores of food. Then there was a wet period, which corresponded to a higher dependence on agriculture and a population boom. When that wet period ended with a long drought, the high population and the dependence on agriculture and stored food made the people less able to adapt to the drier conditions and they were forced to leave.

We have not actually read this book yet, though we’ve requested it and may have read it by the time we have our discussion. We found out about this book from a book review in QR. The book review says that this book does an excellent job of making available to the scientific community a huge wealth of information, including "palynological, dendroclimatological, and meterological data to provide a paleoenvironmental context for the occupation of the region by Pueblo Indians from 700 to 1300 AD." Petersen sees that the climax of the Anasazi culture occurred during the Medieval warm period, but from the review we cannot tell if he makes any postulation on why they ended up abandoning the Plateau.

Written by an Outside Magazine contributor, this is an easy-to-read and interesting narrative of one man’s quest to find out as much as he can about the Anasazi. He talks about what people know about the Anasazi, what they don’t know, and the history of archaeology in the area. Why did they move from the valleys onto the cliffs? Why did they end up leaving the cliffs? How were they all connected to each other through the Chacoan system? What are those roads for? What role did environment play? What role did religion play? What role did cannibalism and domination through fear play? Roberts discusses all these questions and ultimately comes to the conclusion that no one really knows just yet. Roberts presents arguments from all sides regarding why the Anasazi moved up into the cliffs (were they defensive sites, or religious sites? Did very many people REALLY move into cliff dwellings?) and whether the Anasazi society was peaceful (they were portrayed as such for a long time, only relatively recently are the massacres and cannibalism coming to light). With respect to why the Plateau was abandoned, Roberts presents the argument from Bill Lipe that there must have been some sort of "pull" on the people to move, not just some "push" from environmental stress. The "pull," they think, was the Kachina phenomenon–a new religion based on the existence of many many supernatural beings and the rituals associated with those beings. The original move to the cliffs was associated with a return to old Chacoan ways of living (some sort of escape from the Kachina phenomenon) and subsequent abandonment (acceptance of the Kachinas). These rituals could have brought communities together in such a way that they WANTED to move to other areas to be with other people.

Drawn from his book, In Search of the Old Ones, this article discusses the pre-, during-, and post-Chaco culture of the Anasazi. He talks about the various causes for their abandonment of the Colorado Plateau, including both "push" (environment, warfare, disease) and "pull" (religion) theories. He discusses the Chaco culture itself, including evidence of cannabalism; and the onset of the Kachina Phenomenon, which followed it. There is still a lot left to learn about both the Anasazi and the role the Chaco culture played in their eventual abandonment of the CO plateau. Really, archaeologists are still very unconvinced about any of the theories of abandonment. This article was fun to read (as most National Geographic articles are) and has lots of really beautiful photographs–people who are interested in this stuff should really find the original.

This book is mainly written for other archaeologists. It gives a very detailed and thorough study of the Black Mesa Anasazi, especially regarding culture, demography, hunting and gathering patterns, and the seasonality of their behavior (did they live in certain places at certain times of the year?). Powell goes through all the different phases of development of the Black Mesa Anasazi, including population problems, rainfall and climate patterns, and the availability of vegetation. Powell uses a variety of statistical analyses in order to support each conclusion.

This is a transcript of a panel discussion in which people discussed the reasons for the migration of the Anasazi. This little book is interesting because the panelists bring in a number of different opinions (from a Zuni man (and scientist) who says that they were searching for "the center," to archaeologists who don’t have such a strong opinion about anything and really just don’t know for sure). It’s an easy read, and kind of amusing to read a transcript of people talking, rather than what somebody wrote. I’m including it here because I went to the trouble of getting it from interlibrary loan, but it really doesn’t have that much information in it.

The authors use oxygen isotopes from a 6 m sediment core from lake Punta Laguna in southern Mexico to determine periods of aridity and humidity during the last 3,500 years. They correlate these data with the archaelogical record of the Mayan civilization during that time. Oxygen isotopes in lakes become "heavier" during times of relatively high evaporation (and by inference, drought or dry conditions) because the lighter ¹⁶O isotopes have a higher vapor pressure and evaporate more readily than do their heavier brethren. Curtis et al. have picked out of the core, specific taxa that make shells in equilibrium with the ambient water. They have also ¹⁴C dated the core, and corrected for a "hard water" effect common in CaCO₃-rich waters such as these. Based on the isotopic records and the radiocarbon dates, they recognize that from about 1600 BC to 300 AD EP conditions were like those of today (fairly wet). From 300 AD until 1100 AD, the climate was much drier (including at least 3 prolonged droughts). From 1100 until now, conditions were consistently wetter. The collapse of the Mayan civilization occurred during the latter stage of the dry period. This paper was exceptionally-clear and easy to follow. The methods section was particularly well-written and answered a lot of questions before you could think to ask them.

In a study very similar to Curtis et al., (1996) paper, these researchers develop an ¹⁸O chronology for Lake Chichancanab ("Sport Utility Vehicle" in Yucatec Maya) in southern Mexico. They measure the ¹⁸O on shells, and also measure CaCO₃ and S in the sediments (in times of excessive dryness, both calcite and gypsum are precipitated in this lake). The temporal resolution in this 4.9 m core is not as precise as in Lake Punta Laguna (it has been ¹⁴C dated back to around 9200 BP). With these data, they get a picture of EP variability throughout the last 9200 years. The find that conditions were like today, except for a period between 1300-1100 BP, which was dryer.

Rue took cores from Petapilla Swamp (1.3 m core) and Lake Yojoa (1.5 m) in order to extract a pollen record. The cores were ¹⁴C dated (back to ~1000 BP and 5000 BP respectively) and show evidence of slash-and-burn agriculture during the Mayan civilization. They say that they do not see any evidence of climate-induced changes in flora, which makes them think that all palynological change was due to anthropogenic causes (we think this is a little sketchy). They use the palynological evidence tell when forests were cleared and when crop plants were established. We looked up and included this paper because Sabloff refers to it, and because it discusses how we can see evidence of agriculture in the pollen record.

The main point of this commentary is to review past interpretations of Mayan civilization and change. Sabloff highlights some of the new findings, including some pollen work (Rue, 1987) which indicate that Mayans used slash and burn agricultural practices. Ecological stress and degradation were very important in the collapse of Mayan civilization, especially in the southern lowlands of the Yucatan (an area particularly hard-hit by environmental degradation).

Again, Jeremy comes through with a witty and insightful commentary on recent understandings with respect to the collapse of the Mayan civilization. We liked this short essay because it puts the Curtis et al. (1995) work into a broader Mayan perspective. It raises the question of the importance of the effect of internal cultural stresses on how well a society can adapt to environmental change.

Lean and Warrilow have created a numerical model which predicts the effect of deforestation of the Amazon rainforest on climate. They use an atmospheric global climate model (a 3 yr. simulation) where they replace the tropical rainforest and savanna with pasture. The end result is in less precipitation and evaporation, decrease in soil moisture, and an increase in surface temperature. These are mainly a result of the changes in surface roughness (decreased evaporation and increase in temp.) and in albedo (decrease in moisture flux). This paper just tells us that humans can have a fairly profound impact on environment and climate–it doesn’t just go the other way (but we knew that already). Curtis et al. (1996) referred to this article in their paper, which is why we checked it out.

This article was remarkably easy and fun to read, and if it weren’t 22 years old we may have had the class read this one. It traces the evolution of humans from their origins to the present, and gives the geologic conditions and context for that evolution (geology is in the broad sense–tectonics, atmosphere, climate). It did not really get into causal relationships (such as: people lived in caves because it was chilly outside) but rather discussed observations (during the Pleistocene, it was cold in northern Europe, and people lived in caves then). This paper is nice in that it draws from many data sets from around the world (from austrolapithacus fossils in Eastern Africa to cave paintings in Lascaux, to stone tools found in the Americas).

These folks looked at human remains (well, campsites) found in debris flow deposits in a particular valley within the Atacama desert in northern Chile They postulated that this region formed some of oasis in this really dry region, containing more plants and animals than the surrounding region. Therefore, people tended to make camp there. They determined that major storms must have triggered debris flows every 500-1200 years, and moderate storms came every 100-200 years (also triggering debris flows, but smaller ones). This paper was confusing in that we had a tough time figuring out how they tried to correlate climate patterns to human demographic patterns.