Two Indonesian tsunami warning buoys, put in place after a 2004 earthquake and tidal wave killed more than 230,000 people, failed to activate on Oct. 25 when a 7.7 magnitude temblor hit the country’s Mentawai Islands. This time, more than 400 died. Even if the buoys had been operational, islanders would not have had enough time to evacuate, since the earthquake that triggered the tidal wave occurred too close to shore, according to the U.S. National Weather Service. After the 2004 event, the U.S. National Oceanic and Atmospheric Administration donated two Deep-ocean Assessment and Reporting of Tsunamis (DART) buoys to
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.