A billow destroyed a 20-meter-long (66-foot-long) esplanade in Sokcho Beach, Gangwon, on Saturday. The 80-meter-long stretch of the same esplanade collapsed due to billows on Nov. 16. [YONHAP]
Dictionary.com tells me that 'billow' is the right word: it means a great wave. Still, I think someone at Yonhap or Joongang is depending too much on dictionaries.
Anyway, while I do expect that the proximate cause was a billow, the ultimate cause was smaller waves slowly eroding the beach over several months so that one wave could later complete the job.