The precise cause of the disaster is contentious. EPM’s manager, Jorge Londoño, told local media that “unpredictable geological conditions” had caused the tunnel to fill and then collapse over the weekend, while activists argue that it was caused by an accumulation of plant material left uncollected by the company. Swaths of surrounding dry tropical rainforest was deforested to clear space for the dam’s reservoir.
The crisis had been brewing since late April, when a blockage in the diversion tunnel was breached, causing water levels to rise both up- and downstream.
https://www.theguardian.com/world/2018/may/16/colombia-tens-...
Судя по всему строительный туннель забился мусором и из-за этого ему не хватило пропускной способности пропустить паводочный расход. Пишут, что это все началось еще с апреля, а сейчас напор воды "пробил" засор. Вот )