Date of Award

12-2015

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Quaternary and Climate Studies

Advisor

Daniel H. Sandweiss

Second Committee Member

Alice R. Kelley

Third Committee Member

Gregory Zaro

Additional Committee Members

Daniel F. Belknap

Abstract

The El Nino global climate anomaly is a major cause of weather variation that can have far-reaching effects on human populations around the world. Northern coastal Peru is an area of historically major impacts where strong El Nino events have resulted in catastrophic flooding and mass wasting, leading to significant social disruption. There is a growing body of literature on the prehistoric chronology of El Nino and how it affected human populations of the past, but more work is needed. In order to address the timing and characteristics of past El Nino events I investigated the alluvial sedimentary sequences at two archaeological sites of the Moche Period, San Jose de Moro and Huaca del Sol, to infer patterns of past El Nino flooding. Both sites are located adjacent to braided rivers and are constructed on floodplains composed of thick alluvial sequences that are reflective of some aspects of the region’s past climate.

San Jose de Moro is located along the Chaman River, just north of the city of Chepen. Due to the limited size of the river’s drainage basin and the extremely dry nature of the regional environment, flooding is limited to periods of El Nino rainfall and all alluvial deposits at San Jose de Moro are thus thought to be El Nino related. The exposed sedimentary sequence at the site reveals a prominent shift from broad, relatively flat floodplain deposits to cross-bedded, channelized deposits, which may have resulted from several causes, including channel avulsion, a change in stream character related to vegetation stabilization, a change in river base level, stream capture, or a change in climate resulting in an increase in the intensity or frequency of precipitation events. An increase in precipitation may be related to an increase in El Nino activity.

Huaca del Sol is located along the Moche River, near the city of Trujillo. The Moche River has a much larger drainage basin and extends much higher into the Andes Mountains than the Chaman River. Because of this, flooding may be caused by non-El Nino events but El Nino is still one of the major sources of flooding within the drainage. At Huaca del Sol the stratigraphic sequence has significant textural variation throughout, and is consistent with a pattern of regular shifting and avulsion characteristic of braided streams. There is thus no clear evidence of any environmental changes having a significant effect on the stratigraphic sequence at the site.

Both San Jose de Moro and Huaca del Sol are located on floodplain surfaces created at least in part by El Nino-driven aggradation that produced broad, elevated areas with decreased risk of El Nino flooding. The presence of these sites on this landscape shows that this environment was attractive for both occupation and ceremonialism. These results demonstration that in addition to being a cause of weather variation and catastrophism, El Nino should also be seen as a constructor of favorable landscapes that is essential to understanding the physical setting of prehistoric human settlements in northern coastal Peru.

Comments

As of 2002, Degree of Master of Science (MS) Quaternary and Climate Studies published under the auspices of the Climate Change Institute.

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