The first waves rolled ashore in Banda Aceh, on the northern tip of Sumatra, barely 20 minutes after a magnitude 9.1 megathrust earthquake struck the Indian Ocean on 26 December 2004. After the last of a series of tsunamis slammed the community, the death toll in Indonesia exceeded 150,000.
Following the so-called Boxing Day tsunamis, survivors opted to rebuild their lives within the inundation zone rather than abandon the exposed coastline. Now, scientists have used archaeological evidence from the coast of Sumatra dating back to the 14th century to show that returning to a tsunami-devastated region has a long historical precedent. Their results were published last month in the Proceedings of the National Academy of Sciences of the United States of America.
No Shortage of Tsunamis
Patrick Daly, an archaeologist at Nanyang Technological University in Singapore and lead author of the new study, works just across the Strait of Malacca from the Indonesian island of Sumatra. He remembers visiting Banda Aceh, the capital of Indonesia’s Aceh Province and the site of some of the worst destruction from the 2004 Indian Ocean tsunami, in 2006.
Seeing the extensive wreckage firsthand got Daly thinking about how frequently tsunamis strike the region. “Have there been other societies that have dealt with similar things?” he remembers wondering.
The answer, Daly and his colleagues soon realized, was a definitive yes. In a study published in 2017, a team of researchers, including Daly, found evidence that 11 tsunamis had struck near Banda Aceh between 7,400 and 2,900 years ago. Other research teams analyzing sand deposits and growth patterns of corals suggested that tsunamis also struck the area more recently, in about 1394 and 1450. Daly and his collaborators set about looking for archaeological evidence from the 14th and 15th centuries to determine the impacts of these more recent tsunamis.
Sherds, Sherds Everywhere
The scientists examined a 40-kilometer section of the Sumatran coastline near Banda Aceh.
Working with a team of over 60 Acehnese individuals recruited through the International Centre for Aceh and Indian Ocean Studies, they collected more than 30,000 pieces of broken ceramic pottery (sherds). The team found the roughly 5- to 15-centimeter fragments, which had been exposed by erosion and the 2004 tsunamis, both on the ground and in beach-facing cliff faces. These pieces were trade ceramics, the researchers concluded, and were originally made in places as far-flung as China, India, Syria, Thailand, and Vietnam. They were “the type of stuff you’d find in museums of Asian art,” said Daly.
On the basis of the style and design of the pottery, the team grouped the sherds into five time periods ranging from pre-1400 to 1650–1800.
The researchers found that the ceramics tended to be clustered in sites, implying geographically distinct settlements engaged in trade. These settlements, 10 in total, likely corresponded to modest-sized fishing villages, the researchers concluded. Nine were located within the inundation zone of the 2004 tsunami, and the 10th was situated on a promontory roughly 60 meters above sea level.
Trading from a Hill
Mining through their extensive database of age-dated, geographically tagged sherds, Daly and his collaborators noted a curious result: The settlements contained over 3,800 sherds confidently dated to before 1400 but only 70 sherds confidently dated to 1400–1450.
This fiftyfold decrease was consistent with the occurrence of a tsunami in 1394 that temporarily wiped out trading, the team reasoned.
“A powerful tsunami in the middle ages around 1394, analogous with the 2004 event, does indeed give the best fit with the detailed archaeological data set, ” Hendrik J. Bruins, a geoarchaeologist at Ben-Gurion University of the Negev, Israel, who was not involved in the research, told Eos.
Further support for this hypothesis soon emerged: 56 of the 70 sherds dated to 1400–1450 were found at the 10th settlement, the one atop the promontory and therefore presumably above the reach of tsunami waves. “Cluster 10 clearly retained connections to its international trading partners over this period,” the researchers wrote.
Daly and his colleagues went on to find that the hilltop settlement was abandoned by roughly 1550. Around the same time, trade started to increase at the low-lying villages, sites that would have likely been destroyed by the 1394 tsunami. Researchers don’t know what caused the shift in trading patterns, but Daly and his team hypothesize that outsiders may have been moving into the low-lying settlements.
“You’re getting new groups of people taking advantage of the depopulation to set up a new trading infrastructure,” said Daly.
The area around Banda Aceh is an ideal meeting place for traders, he said, because it’s situated near the Bay of Bengal and therefore readily accessible from India, China, and Southeast Asia.
The results in the new paper show that there’s a long history of people moving back into tsunami-prone regions after a disaster, said Daly. That’s partially because there are “massive social and economic consequences to relocating people.” Humans are also remarkably good at accepting a certain degree of risk, particularly for rare events like tsunamis, Daly said.
The Acehnese coast will surely be hit by another tsunami in the future, said Daly, who notes that only time will tell if people will once again rebuild in such a disaster-prone area. He and his team are continuing to piece together the tsunami record in the area, particularly focusing on the last 2,000 years, he said. “We’re telling this big archaeological, environmental story.”
—Katherine Kornei (@katherinekornei), Freelance Science Journalist