Between 150 and 950 A.D., five serious droughts struck the area that is now New Mexico. Each time this happened, new research published in the journal Scientific Reports reveals, the region’s inhabitants lit ice blocks found in lava tubes—cavernous, cylindrical passages formed by rivulets of flowing lava—on fire to collect drinking water.
For the study, researchers extracted an ice core from a frigid lava tube buried almost 50 feet underground at El Malpais National Monument.
“We started seeing these dark areas,” lead author Bogdan Onac, a geoscientist at the University of South Florida, tells Isaac Schultz of Atlas Obscura. “I said, ‘Wait a minute. Something is going on—why is it black here?’”
The dark marks turned out to be bands of soot and charcoal. Using radiocarbon dating, the team found that the bands corresponded with years that scientists knew droughts had occurred.
Kenny Bowekaty, an archaeologist and tour guide who is a member of the Ashiwi people of the Pueblo of Zuni, tells E&E News’ Jacob Wallace that ancestral Puebloans probably used the icy corridors for religious purposes, in addition to gathering water and storing animals they hunted.
“Ice to the Ashiwi people is still a resource of life,” Bowekaty, who was not involved in the new study, says. “There’s a lot of compounded uses for what would have been considered ice caves.”
He adds that the Ashiwi continued making religious pilgrimages to the ice tubes until the early 1900s. More recently, though, melting ice has forced them to restrict travel to the caves.
Per Science News’ Rachel Fritts, the research team traveled to the site in 2017 with the intention of studying ice cores to learn about ancient climates. The shape of the tubes, carved out in the landscape by long-ago lava flows, helps keep ice frozen by pushing hotter air up and out of the cave and making cooler, denser air sink. Atlas Obscura notes that the National Science Foundation, the National Park Service and the Western National Parks Association backed the project in an attempt to document secrets held in the ice before they’re lost to climate change. The ice block studied by the team has already shrunk from around 35,000 cubic feet to less than 1,800.
Based on pottery shards found near cave entrances and ancient road networks that cross the area, researchers had previously suspected that ancient people harvested water from the caves. But this is the first time scientists have been able to connect water collection to periods of droughts. In addition to charcoal pieces, the team found a pottery shard dated to 1097 A.D.—likely evidence of the use of vessels to collect water.
People have resided in the El Malpais area for more than 10,000 years, with the largest ancient populations living there between 950 and 1350 A.D., according to the National Park Service. During that era, the region was connected to the Chaco system, a political, economic and religious culture centered about 80 miles north. The ancestral Puebloans of El Malpais built complicated multi-story buildings in the Chaco style. Around 1250, the local communities appear to have dispersed, with people resettling in the pueblos of Acoma to the east and Zuni to the west. The Zuni-Acoma Trail, a more than 1,000-year-old highway in the area, cuts through the lava flows of El Malpais.
“This study demonstrates the ingenuity of indigenous people who used the area,” Barbara Mills, an anthropological archaeologist at the University of Arizona who was not involved in the study, tells Science News. “It also shows how knowledge about the trails, caves and harvesting practices was passed down over many centuries, even millennia.”