The Disappearance of the Anasazi—How much is really mystery?

 

In “The Ancient Ones: The Anasazi and Their Neighbors, “ chapter four of his book Collapse, How Societies Choose to Fail or Succeed, Jared Diamond synthesizes the archaeological research on the Southwestern US communities that flourished and then seemingly “vanished.” Diamond believes that communities need to maintain self-sufficiency in order not to collapse. He contends that when societies become dependent upon importing their needed resources, they become more vulnerable to collapse.

His thesis is that Chaco Canyon was abandoned because of BOTH the human impact on the environment and because of drought. The drought was the last straw or “proximate” cause of collapse for a society that had become overpopulated for the amount of resources it had to maintain self-sufficiency. With the increase in population due to their success at managing water and goods and developing an intricate and complex society, the society starved when drought became severe, and they had no other resources to draw upon since they had ruined the soil, deforested the region, and were dependent upon “outliers” who probably revolted to support them.

The collapse of the Anasazi communities illustrates the theme of human environmental impact and climate change intersecting, environmental and population problems spilling over into warfare, the strengths but also the dangers of complex non-self –sufficient societies dependent on imports and exports, and societies collapsing swiftly after attaining peak population numbers and power.

 

Diamond references a great deal of research regarding these features to help us understand how communities like Chaco Canyon were able to survive successfully for six hundred years but then suddenly fail:

 

  1. Dating of tree rings
  2. Dating of packrat middens
  3. Artifacts, including pottery and “luxury” items, such as turquoise and shells
  4. Human remains, dated and studied
  5. Human middens

 

Although they were a relatively small society, the Anasazi constructed in stone the largest and tallest buildings erected in North America until the Chicago steel girder skyscrapers in the 1880’s

 

Anasazi structures can be dated to within a year, enabling us to understand the societies’ histories pretty finely

 

The cultures and societies of the American Southwest are numerous (approximate dates of collapse): Mimbres (1130 AD)

Chaco Canyon, North Black Mesa, Virgin Anasazi (middle or late 12th century); Mesa Verde and the Kayenta Anaszi (1300); Mogollon (1400), and Hohokam (15th century)

They did not vanish as a people; they were incorporated in communities such as the Hopi and Zuni pueblos.

 

 

The Fundamental problem: the US Southwest is a fragile and marginal environment for agriculture, with low and unpredictable rainfall, quickly exhausted soils, and very low rates of forest regrowth. Environmental problems, especially major droughts and episodes of streambed erosion, tend to recur.

 

Packrat middens: a virtual time capsule of plants growing within a few dozen yards of the midden. Paleobotanists can reconstruct changes in local vegetation.

Tree rings: archaeologists can date building sites to the nearest year by the tree rings of the site’s wood construction beams.

Tree rings: because rainfall and temperature vary seasonally in the SW, tree growth rates also vary seasonally. The dry climate results in excellent preservation of wooden beams from trees felled over a thousand years ago.

            Width of rings vary according to the amount of rainfall. Narrow rings means drought; wider rings indicate a wetter year, so tree rings also give us a picture of the past climate.

 

Origins and Agricultural Beginnings: 11,000 BC: first humans reached the Americas with colonization of the New World from Asia by peoples ancestral to Native Americans (this theory is disputed by some Native American communities). Agriculture arrived from Mexico, where corn (arrived 2000 BC), squash (800 BC), beans (later), and cotton (400 AD) were domesticated. By AD 1, Native Americans were in residence in villages in the SW, and were primarily dependent upon agriculture with ditch irrigation. Their populations exploded until the retrenchments began around 1117 AD.

 

Three types of agriculture emerged to cope with water management problems:

  1. dryland agriculture: relied on rainfall at higher elevations where there really was enough water to grow crops. The Mogollon used this practice at Mesa Verde. Risk: too cool to grow plants.
  2. planting in areas where the ground water table was close enough to the surface to nourish plants’ roots. This method was employed in canyon bottoms with intermittent or permanent streams, such as Chaco Canyon. Risk: this process worked during wet years; when drought recurred, the newly expanded population could not be fed and thus starved and the society collapsed. Solution: move frequently. This became impossible as populations grew too large to shift successfully. Solution: plant in a variety of places. This worked for awhile in Chaco Canyon, but required a complex political and social system for distributing food among the different sites. When the complex system collapsed, people starved.
  3. Collecting water runoff in ditches or canals, a method used in Chaco Canyon and by the Hohokom. Risk: the human cutting of ditches results in sudden heavy water runoff from rainstorms, leading to cutting deep channels in the ditches, called arroyos. With the water now running deeply, the water level dropped below the fields and thus irrigation became impossible without pumps. Second risk: irrigation can wash away the dams and channels. 
  4. A different and successful strategy used by the Hopis and Zunis, communities that still flourish today: plant corps and live near permanent and dependable sources of water, but on landscape “benches” above the main floodways and thus avoid washing away the fields and villages. Also, practice a diverse economy, exploiting ecologically diverse zones, so that each settlement would be self-sufficient.

 

Focus on Chaco Canyon

 

Flourished from AD 600 until 1150-1200, deeply advanced, largest buildings in pre-Columbian North America

Today: treeless landscape, deep-cut arroyos and sparse low vegetation

Completely uninhabited except for NPS rangers’ houses

AD 600—lived in underground pit houses, like other SW Native American communities

AD 700—invented techniques of stone construction

AD 920—Pueblo Bonito: two stories, ultimately five or six stories, with 600 rooms, and logs as roof supports weighing up to  700 pounds

At first, this was an environment with advantages:

  1. narrow canyon caught runoff, creating high alluvial ground-water levels and high rates of soil renewal (good water, good dirt)
  2. high diversity of plant and animal species (deer)
  3. low elevation and long growing season
  4. originally had nearby juniper and pinyon pine woodlands for construction logs and firewood. Pinyon pinenuts also provided protein (75%)

 

Major disadvantages:

  1. water management and use of channel irrigation resulted in deep arroyos around AD 900. With water levels below field levels, irrigation was impossible until arroyos filled again. Arroyo cutting develops very suddenly. To compensate for the arroyos, the Chaco Anasazi stored rainwater by building dams inside side-canyons above the elevation of the main canyon. They also laid out field systems that rainwater could irrigate, and they stored rainwater that came down over the tops of cliffs, and they built a rock dam across the main canyon. Images of floods:

 http://www.chacoarchive.org/gallery.html

 

  1. deforestation. We know there was deforestation because of the chemical composition of the packrat middens. Packrat middens were first found in 1849 by gold miners who thought they’d try eating them—they’re sweet but make you nauseous because they’re full of  dried rat urine, rat feces and rat garbage (packrats gather sticks, plant fragments, mammal dung: the dried urine cements it all together into a tempting ball). The midden can be radiocarbon-dated. They found pine needles in the middens in 1975 in middens collected at the NPS campground near Pueblo Bonito. They knew, then, that the middens were over a thousand years old, and that there had been a pinyon pine  and juniper forest within yards of Pueblo Bonito at that time. Middens dated to before 1000 AD still had pine needles in them; after that, they do not.  Chaco Canyon was quickly deforested because it is a dry climate where the rate of tree regrowth cannot keep up with the rate of logging.

 

http://www.nps.gov/chcu/photosmultimedia/photogallery%2Ehtm?eid=144965&root_aId=205#e_144965

images of Pueblo Bonito

 

rain in 2006

 

http://www.friendofchaco.org/2006%20Rains.html

 

http://sbsc.wr.usgs.gov/cprs/research/projects/global_change/middens.asp

packrat middens

 

Paleo slide set

 

http://www.ncdc.noaa.gov/paleo/slides/slideset/index16.htm

 

 

Construction practices changed: the inhabitants went to mountains up to 50 miles away to haul logs, without draft animals, of ponderosa pine, spruce, and fir trees.  By analyzing isotopes of strontium, researchers concluded that the Chaco Canyon Anasazi were hauling logs from Chuska Mountains and the San Mateo Mountains.

1029 AD: population still increasing in Chaco Canyon—big spurt of construction—built the Great Houses and hundreds of small settlements on the south side of the canyon. Archaeologists guess at a population around 5000-some argue more, some less.

 

Development and Reliance upon Outlying Communities

 This population survived for awhile by relying on outlying satellite settlements—where it might rain and thus they would have a food surplus to share with the major settlement in Pueblo Bonito-- joined to Chaco Canyon by miles of roads still visible today.

 

Collapse: Chaco Canyon had to import its goods but it exported nothing. Imports included pottery, stone, turquoise, macaws, shell jewelry, copper bells, and food. A mini-empire resulted, with those elite living in luxury at Pueblo Bonito and outlying “peasants” much less well-fed but raising the food. We know this from studying the garbage in the various locations and the burials: the “outliers” had a higher rate of infant mortality, were more anemic, and were shorter than those people at Pueblo Bonito.

 

What happened? Warfare and starvation, leading to cannibalism (controversial). People were eating mice whole; evidence of cannibalism resulting from murders during war (unburied bodies, skulls with cut marks caused by scalping, skeletons were arrowheads inside the body cavity, proliferation of defensive walls, bones with smooth ends—hallmark of boiling in pots—bones cracked to extract marrow—residues of the human muscle protein myoglobin on the pots’ insides, dried human feces containing human muscle protein, normally absent from human feces)

Drought: AD 1130. Sometime between AD 1150 and 1200, Chaco Canyon was abandoned and remained empty until Navajo sheepherders reoccupied it 600 years later.

 

The moral of the story: we can get away with a lot of waste when times are good.

“We forget that conditions fluctuate, and we may not be able to anticipate when conditions will change. By that time, we may already have become attached to an expensive lifestyle, leaving an enforced diminished lifestyle or bankruptcy as the sole outs” ( 156)