The carnage of the tsunami in Indonesia at the end of 2018 has triggered a global awareness in preparing for unexpected natural disasters. The tsunami was unusually triggered by the collapse of an erupted volcano, leaving everyone on the coast of Jakarta unguarded.

The tragic losses in Indonesia and the safety concerns along the coastline raise the question of whether China also faces the risk of tsunamis. The question remained in the dark due to the lack of reliable historical records and geological investigations in the past. However, a recent study published by researchers from the University of Science and Technology of China indicates that a tsunami severely threatened the coastline of Chinese mainland  about a thousand years ago.

The study is based on previously discovered evidence on Dongdao Island of Xisha Islands in the South China Sea, which suggests that a tsunami occurred in the South China Sea around 1024. The research team conducted geological investigations on Nan'ao Island of Guangdong Province in southern China. The goal was to see if there was any new evidence that might suggest if the coastline could face the risk of a similar type of tsunami that once battered Dongdao Island.

Historical records

The risk of large tsunamis in the South China Sea is often underestimated and not recognized since there were barely any reliable or detailed written records that have documented devastating tsunamis in the region.

After sorting out and categorizing historical records on tsunamis in the past 1,000 years, researchers have found the earliest written records of a suspected tsunami event along the coastlines of Chinese  mainland was in November 1076 in South China's Guangdong Province. The date is not far from the known tsunami on Xisha Islands, which suggests that the tsunami might have influenced the creation of islands in the South China Sea and the coastlines of Chinese mainland .

However, due to the ambiguity of ancient Chinese language, scientists think that the written record might have referred to a storm surge instead of a tsunami. A storm surge is caused by hurricanes and happens more often than tsunamis, and usually only affects areas along the coastline while a tsunami results from the displacement of water either by earthquake, volcanic eruption, landslide or meteorite impact. Tsunamis can reach thousands of kilometers from the coastline and cause much more damage and loss of life than the storm surge.

Discoveries

The historical records, ambiguous as they were, provided researchers with direction. They chose Nan'ao Island in Guangdong Province as the site for the study. Nan'ao Island lies in the northern region of the South China Sea and is three to eight kilometers off the coast of Guangdong Province. The excavation of Nan'ao One, a late Ming Dynasty (1368-1644) shipwreck two kilometers south off the island, confirmed the geological importance of Nan'ao Island in the ancient Chinese marine silk road.

However, based on the examination of sediments and cultural relics, the researchers found that there was a significant decrease in numbers of relics since the Song Dynasty (960-1279) until the Ming Dynasty. Formation of sedimentary samples indicates that there was indeed a tsunami instead of a storm surge. Therefore, scientists concluded that there were around 500 years of cultural decline on this island until the late Ming Dynasty caused by a devastating natural disaster, a tsunami. 

The risk of large tsunamis in the South China Sea primarily comes from the Manila trench that lies in the Philippines. It is often associated with frequent earthquakes and volcanic activities.

The study reveals the possibility of a tsunami in the South China Sea and calls for attention in preparing for this destructive natural disaster, and evaluation of whether infrastructure projects along the coastlines would be able to sustain the risk of being struck by a tsunami.