One afternoon last year, Ha Thi Be, 67, was sitting with her son in her tiny coffee shop in the town of Hong Ngu, looking out on the lazy Tien River, the main branch of the Mekong in Vietnam. Suddenly, the ground beneath them gave way. The river bank was crumbling into the water. “We shouted out loud and ran,” she says. “It crashed with a huge sound, boom, boom, boom.”

Be and her son escaped unharmed, but the coffee shop and her nearby house were destroyed. “It took all of what we owned to build the house, and now it's all gone,” she sighs. Still, Be counts herself lucky. “If it had happened at night, I and my