Geoscientists discover Ancestral Puebloans survived from ice melt in New Mexico lava tubes
A lava tube in the El Malpais National Monument yields centuries-old
insights of survival in the face of harsh climate change

Date:
November 18, 2020
Source:
University of South Florida (USF Innovation)
Summary:
New study explains how Ancestral Puebloans survived devastating
droughts by traveling deep into the caves of New Mexico to melt
ancient ice as a water resource.



FULL STORY ==========================================================================
For more than 10,000 years, the people who lived on the arid landscape of modern-day western New Mexico were renowned for their complex societies,
unique architecture and early economic and political systems. But
surviving in what Spanish explorers would later name El Malpais, or the
"bad lands," required ingenuity now being explained for the first time by
an international geosciences team led by the University of South Florida.


========================================================================== Exploring an ice-laden lava tube of the El Malpais National Monument and
using precisely radiocarbon- dated charcoal found preserved deep in an
ice deposit in a lava tube, USF geosciences Professor Bogdan Onac and his
team discovered that Ancestral Puebloans survived devastating droughts
by traveling deep into the caves to melt ancient ice as a water resource.

Dating back as far as AD 150 to 950, the water gatherers left behind
charred material in the cave indicating they started small fires to
melt the ice to collect as drinking water or perhaps for religious
rituals. Working in collaboration with colleagues from the National
Park Service, the University of Minnesota and a research institute from Romania, the team published its discovery in Scientific Reports.

The droughts are believed to have influenced settlement and subsistence strategies, agricultural intensification, demographic trends and migration
of the complex Ancestral Puebloan societies that once inhabited the
American Southwest. Researchers claim the discovery from ice deposits
presents "unambiguous evidence" of five drought events that impacted
Ancestral Puebloan society during those centuries.

"This discovery sheds light on one of the many human-environment
interactions in the Southwest at a time when climate change forced people
to find water resources in unexpected places," Onac said, noting that
the geological conditions that supported the discovery are now threatened
by modern climate change.

"The melting cave ice under current climate conditions is both uncovering
and threatening a fragile source of paleoenvironmental and archaeological evidence," he added.



==========================================================================
Onac specializes in exploring the depths of caves around the world where
ice and other geological formations and features provide a window to
past sea level and climate conditions and help add important context to
today's climate challenges.

Their study focused on a single lava tube amid a 40-mile swatch of
treacherous ancient lava flows that host numerous lava tubes, many with significant ice deposits. While archaeologists have suspected that some
of the surface trails crisscrossing the lava flows were left by ancient inhabitants searching for water, the research team said their work is
the earliest, directly dated proof of water harvesting within the lava
tubes of the Southwest.

The study characterizes five drought periods over an 800-year period
during which Ancestral Puebloans accessed the cave, whose entrance sits
more than 2,200 meters above sea level and has been surveyed at a length
of 171 meters long and about 14 meters in depth. The cave contains an
ice block that appears to be a remnant of a much larger ice deposit
that once filled most of the cave's deepest section. For safety and conservation reasons, the National Park Service is identifying the site
only as Cave 29.

In years with normal temperatures, the melting of seasonal ice near cave entrances would leave temporary shallow pools of water that would have
been accessible to the Ancestral Puebloans. But when the ice was absent
or retreated in warmer and dryer periods, the researchers documented
evidence showing that the Ancestral Puebloans repeatedly worked their
way to the back of the cave to light small fires to melt the ice block
and capture the water.

They left behind charcoal and ash deposits, as well as a Cibola Gray Ware pottery shard that researchers found as they harvested a core of ancient
ice from the block. The team believes the Ancestral Puebloans were able
to manage smoke within the cave with its natural air circulation system
by keeping the fires small.

The discovery was an unexpected one, Onac said. The team's original goal
in its journey into the lava tube was to gather samples to reconstruct the paleoclimate using ice deposits, which are slowly but steadily melting.

"I have entered many lava tubes, but this one was special because of the
amount of charcoal present on the floor in the deeper part of the cave,"
he said. "I thought it was an interesting topic, but only once we found charcoal and soot in the ice core that the idea to connect the use of ice
as a water resource came to my mind." Unfortunately, researchers are now racing against the clock as modern climate conditions are causing the cave
ice to melt, resulting in the loss of ancient climate data. Onac said he recently received support from the National Science Foundation to continue
the research in the lava tubes before the geological evidence disappears.

Joining in the exploration and research were Dylan S. Parmenter, whose
master's degree at USF was on the topic and is now a doctoral student
at the University of Minnesota, Steven M. Baumann and Eric Weaver of the National Park Service, and Tiberiu B. Sava of the Horia Hulubei National Institute for Physics and Nuclear Engineering in Romania. The research was funded by the National Park Service and the National Science Foundation.


========================================================================== Story Source: Materials provided by University_of_South_Florida_(USF_Innovation). Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Bogdan P. Onac, Steven M. Baumann, Dylan S. Parmenter, Eric Weaver,
Tiberiu B. Sava. Late Holocene droughts and cave ice harvesting
by Ancestral Puebloans. Scientific Reports, 2020; 10 (1) DOI:
10.1038/ s41598-020-76988-1 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/11/201118080741.htm

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