Ice deposits in lava tubes as evidence for droughts in the Southwest US

Abstract:

The southwest United States (hereafter the Southwest) has some of the best known and most conspicuous archeological sites in North America. One of the controlling factors in the development of the cultural mosaic in the precontact Southwest was water availability. The type of water resource, as well as its accessibility and reliability, strongly influenced settlement and subsistence strategies, agricultural intensification, ritual activities, demographic trends, and migration from the late Basketmaker II period (ca. AD 300-500) through the early to mid Pueblo to period (AD 750-1000) in the Zuni-Acoma area of the Little Colorado River drainage. Water availability for Native Americans in the Southwest during periods of prolonged droughts is poorly understood as regional hydroclimate records are scant or contradicting. Here, we show that radiocarbon-dated charcoal recovered from an ice deposit accumulated in Cave 29, western New Mexico, provide unambiguous evidence for five drought events that impacted the Ancestral Puebloan society between ~AD 150 and 950. The presence of abundant charred material in this cave indicates that they periodically obtained drinking water by using fire to melt cave ice, and sheds light on one of many human-environment interactions in the Southwest in a context when climate change forced growing Ancestral Puebloan populations to exploit water resources in unexpected locations. The melting of cave ice under current climate conditions is both uncovering and threatening a fragile source of paleoenvironmental and archaeological evidence of human adaptations to a seemingly marginal environment.

This research was funded by the National Park Service (P16AC01228) and NSF-AGS 2024248.