DES MOINES — Authorities say a girl has died after a brick pillar collapsed onto a hammock she and her sister were sharing at their home in Des Moines. The accident occurred a little before noon Saturday. One end of the hammock was tied to a tree, the other end to an unreinforced pillar of bricks. The girl’s 16-year-old sister told police she was on the hammock when her younger sister jumped in, causing the pillar to collapse and bricks to strike the younger girl’s head. The girl died later at a hospital.