ON DEC. 26, 2004, roiling tides as high as 30 metres rushed onto the shores of Aceh, the Indonesian province on the northwest tip of Sumatra.
An undersea earthquake had struck just off the coast and triggered a destructive tsunami, which hit shorelines all along the Indian Ocean as far away as Somalia. More than 160,000 people were killed in Aceh alone, and even more were displaced.
A similar tsunami appears to have wiped out coastal villages in Aceh more than 600 years ago, and the resulting devastation may have played a role in the rise of the powerful Aceh Sultanate, according to new evidence, published today in the Proceedings of the National Academy of Sciences.
In 2006, archaeologist Patrick Daly was working with Acehnese authorities to preserve cultural and religious sites damaged by the 2004 tsunami when he saw beautifully carved historic Muslim gravestones toppled over and eroding away along the coastline.
"To see them thrown up and tossed aside, that was quite heartbreaking," he says.
Daly started wondering how often these tsunamis had happened in the past, and if so, how they affected the people living in Aceh. The northwest tip of Sumatra, where Aceh's capital Banda Aceh is now, was either the first or last port of call for ships crossing the Bay of Bengal, and the Aceh Sultanate that arose there in the 16th century became one of the few southeast Asian powers to successfully resist colonialism for centuries. Archaeologists, however, didn't have much hard evidence for settlements in the area before the 17th century.
Daly, who works at the Earth Observatory of Singapore, and his colleagues at Syiah Kuala University in Aceh began systematically studying the coast, fanning out to about 40 coastal villages to sit down with elders and map any traces of historic human presence, such as gravestones, ceramic fragments, and old mosque foundations.
"The very first map I got back told most of the story," Daly says. "It was stunning. We can see all these very discrete concretions of material along the coast. Ten settlements came up really distinctly."
Tsunamis are giant, powerful waves most often caused by earthquakes beneath the ocean floor. See what causes tsunamis and the importance of evacuating any area under a tsunami alert.
Based on the age of the ceramic scatters in these settlements, the researchers found something even more striking. The coastal villages all seem pop up around the 11th and 12th centuries, but then all nine low-lying settlements along a 25-milesection of coast seem to have been abandoned around 1400.
Recently discovered geologic evidence suggested that a tsunami had struck the region in 1394, but, Daly says, ""We had no idea of the extent of it—how big, how powerful, how destructive was it." The new archaeological evidence suggests the tsunami, possibly par with the 2004 event, destroyed all the low-lying villages in the region.
The one Acehnese settlement that seemed to survive the 1394 tsunami was a hilltop site out of reach of the tides. Daly and his colleagues have identified the settlement as Lamri, a trading site known from historic records on the medieval maritime Silk Road. At Lamri, the researchers found high-end ceramics from all different parts of China and even as far away as Syria that they didn't see in the low-lying villages.
Lamri, however, went into rapid decline around the beginning 16th century. Just a few decades earlier, people had started rebuilding in the villages that had been destroyed by the tsunami. Trade was getting rerouted to those low-lying areas, as evidenced by the uptick in higher quality ceramics and gravestones with names of elites from other parts of the Straits of Malacca, which separates Sumatra from the Malay Peninsula.
Daly and his colleagues don't think the low-lying coastal areas were resettled by local survivors moving back home. Rather, they believe the tsunami destruction offered prime, vacated real estate for Muslim traders who were being displaced elsewhere as Europeans started vying for influence in the region. (The Portuguese conquered the nearby state of Malacca in 1511.) These newcomers may have formed the core of what became the Aceh Sultanate, a powerful Islamic kingdom.
"You can have a tsunami event followed by a period of absolute renaissance and construction," says Beverly Goodman, a geoarchaeologist at the University of Haifa in Israel, who also studies past tsunamis. (Goodman was not part of the study.)
Geologists and archaeologists hope that reconstructing past tsunamis can help us better understand modern risks.
"If we rely only on the record that we're aware of, we end up significantly underestimating how often and how big the impact of tsunamis is around the world," says Goodman.
She noted that because of the 2004 event, Aceh was shown to be very vulnerable. But the same methods of this new study, which Goodman wasn't involved in, could help recognise vulnerability in places that haven't had a recently recorded event.
"This type of research is really important for getting those older records together to better understand what the risk factors are," Goodman says. "Using sediment records and archaeological records is really critical for filling in those gaps."
The greater challenge is perhaps figuring out how to appropriately adapt to very rare events.
"If you tell people that some time in the next couple of centuries there could be another tsunami, but we can't tell you when, and it will wipe the whole area out, a lot of people are willing to live with that risk," Daly says.
Lead Image: Historic grave markers revealed by the 2004 Indian Ocean tsunami prompted researchers to look for evidence of earlier tsunamis.
PHOTOGRAPH COURTESY PATRICK DALY