MELBOURNE, Australia — Authorities fear a second landslide and a disease outbreak are looming at the scene of Papua New Guinea’s mass-casualty disaster because of water streams and bodies trapped beneath the tons of debris that swept over a village, a United Nations official said Tuesday. [time-brightcove not-tgx=”true”] A mass of boulders, earth and splintered trees devastated Yambali in the South Pacific nation’s remote highlands when a limestone mountainside sheared away Friday.