Exploring Climate Events
and Human Development
the move into the cliffs for defense from enemies? Perhaps, but there
are other plausible explanations, like the fact that less labor would
be needed to maintain structures that were protected from the elements,
or that moving into rock shelters kept the population off the best agricultural
lands. Moving into alcoves at the canyon heads also provided reliable
sources of water for the community.
During the 13th Century, the
Ancient Pueblo peoples of Mesa Verde and nearby regions also abandonded
their masonry homes. For many decades the conventional wisdom was that
severe drought pushed them from the region due to crop failures. Paleo
proxy data from tree rings and packrat middens have been used as evidence
that a severe drought had hit the region. Analysis of bones from the inhabitants
which showed malnutrition seemed to confirm the drought theory. (See Johnson,
Other researchers took another look at climate just to make sure they weren't missing something, and Matthew Salzer (2000) noted there was significant volcanic activity, with one particular event-- likely the largest of the Holocene that occurred in 1259 A.D. -- that may have chilled the atmosphere, thereby shortening the growing season and perhaps disrupting normal rainfall patterns. (See Volcanic Aerosols for access to data).
As with many studies of how
humans relate with and are impacted by the environment, the reasons for
the Ancestral Pueblo people's migration south to become the Pueblo peoples
in modern day New Mexico and Arizona are complex and likely not solely
related to one single cause. But because their culture was agriculturally
based and the region was relatively arid, periods of drought and shorter
growing seasons may well have played a significant role in their southward
move. It is known from early Spanish records that later droughts in the
17th century had a devastating impact on the Pueblo villages. (Cordell,
Graphs of paleoclimatic data in the Southwest offer more on the regional climate variability . For more on the Ancestral Pueblo people and how they responded to climate change, visit the Colorado Plateau- Land Use History of North America's website on Climate Change on the Colorado Plateau, the Bureau of Land Management's Anasazi Heritage Center and Mesa Verde National Park.
Other cultures where extended drought has played a role in the collapse of societies include the Mayan, Egyptian and Persian civilizations.
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