Science: On 5 December, the heaviest rains in Colombia’s history triggered a landslide that wiped out a poor hillside community and left more than 145 people dead or missing, writes Sid Perkins for Science. He describes a series of experiments conducted by Richard Iverson and colleagues to try to determine how such sediment flows can grow to monstrous proportions. Iverson is a research hydrologist at the US Geological Survey in Vancouver, Washington.The team’s results were published online yesterday in Nature Geoscience.