What caused an unexpected, record-breaking tidal event on China’s east coast?

Late Monday evening, water began to rise along the coast of the Bohai Sea in northeastern China, as it usually does during high tide.

But the water continued to rise.

Under the cover of darkness, the tidal wave swept across several coastal regions in Liaoning and Hebei provinces, as well as the city of Tianjin, just over 100 kilometers (62 miles) southeast of the capital Beijing. The water quickly flooded the interior, prompting emergency measures and shattering official records.

“Without obvious wind and waves, a sudden rise in water level in such a large area has not been recorded either at home or abroad,” Fu Cifu, head of the Storm Surge Forecasting Office at the National Marine Environmental Forecasting Center, said in an interview with the state news agency Xinhua on Tuesday.