premise: Twenty-six soldiers died on Sunday when a minibus carrying 31 people fell off a 15-meter cliff into a river in Chile's eighth region, 515 km south of Chilean capital Santiago, Chilean radio said.
  The vehicle was carrying the Chacabuco military band from the city of Concepcion to Canete, a town in Arauco province, for a civic event.
  The minivan driver lost control of the vehicle close to the Quelen Quelen Bridge, on Route 160. The bus landed in the Tucapel River, and swiftly sank.
  Fire crews and the Special Operations Group of Chilean police force, the Carabinieri, rescued five people and took them to the Concepcion Regional Hospital.
   What caused the minibus to fall off the cliff?
hypothesis: driver lost control