Extensive Desert ‘Lava Tubes’ Sheltered Humans for 7,000 Years, Archaeologists Find

Formed after volcanic activity, the underground caves periodically hosted early humans and their livestock in Saudi Arabia, facilitating cultural exchange

a person stands in a dimly lit cave
A researcher explores the depths of Umm Jirsan. Green Arabia Project

Each year, researchers, tourists and hikers from around the world visit the Umm Jirsan lava tube system in Saudi Arabia, looking to explore the sprawling network of underground tunnels formed by lava flow millions of years ago. The geological wonder—with passageways covering some 5,000 feet—is located in Harrat Khaybar, one of the country’s largest volcanic fields that last saw an eruption during the 7th century C.E.

Now, a new study suggests prehistoric humans and their livestock periodically lived inside these naturally hollowed-out structures for 7,000 years during the Neolithic Age and the Bronze Age.

From previous research, archaeologists knew ancient humans were present in northern Saudi Arabia. However, the region’s hot, windy and arid conditions have led organic remains to deteriorate over time, leaving lots unknown about these early inhabitants, Vishwam Sankaran reports for the Independent.

But in the cooler, sheltered underground tunnels, prehistoric remains have been better preserved. In the new paper, published last week in the journal PLOS ONE, archaeologists reveal a range of discoveries in Umm Jirsan indicating repeated phases of human occupation of the lava tubes between 3,500 and 10,000 years ago.

“This is really the first clear evidence of people occupying these caves,” lead author Mathew Stewart, a research fellow at Griffith University’s Australian Research Center for Human Evolution (ARCHE), tells the New York Times’ Robin George Andrews.

In the lava tubes, archaeologists discovered human bones, animal remains and stone tools. They also found rock art featuring cattle, sheep, goats and dogs, which aligns with ideas that prehistoric people of the region kept livestock.

“This site likely served as a crucial waypoint along pastoral routes, linking key oases and facilitating cultural exchange and trade,” Stewart says in a statement.

Isotopic analysis of the remains revealed the animals primarily grazed on wild grasses and shrubs, while humans ate a protein-rich diet that centered more foods like dates, figs and wheat over time.

These findings suggest the lava tubes’ early inhabitants engaged in oasis agriculture: farming practices used on fertile lands in otherwise arid regions.

Stewart was also the lead author of a 2021 study published in the journal Archaeological and Anthropological Sciences, which detailed evidence of striped hyenas stockpiling hundreds of thousands of bones belonging to at least 14 species—including humans—in the back of Umm Jirsan over the past 7,000 years.

Archaeologists have investigated the tunnel system since 2007. However, only a small portion has been examined, as researchers first ventured into the cavern’s depths in 2021, as Smithsonian magazine’s Isis Davis-Marks wrote at the time.

researchers in a cave digging
The excavation at Umm Jirsan Green Arabia Project

ARCHE led the new study in close partnership with international researchers and organizations, including the Saudi Heritage Commission, the Saudi Ministry of Culture and the Saudi Geological Survey. The research “represents the first comprehensive study of its kind in Saudi Arabia,” Michael Petraglia, the director of ARCHE and a co-author of the study, says in the statement.

Thousands of volcanic caves like Umm Jirsan exist across Saudi Arabia, and Stewart tells the New York Times the systems “hold huge promise” for understanding ancient humans’ movements and practices.

“As a scientist who works primarily in caves, I am excited that we have another type of cave system being used by past human populations,” Mike Morley, a geoarchaeologist at Flinders University in Australia who was not involved with the study, tells New Scientist’s James Woodford. “These finds represent a treasure trove of archaeological information for Arabia, a massive region that has only recently been investigated systematically for prehistoric archaeology.”

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