An Iowa community was shut down much of Sunday afternoon while emergency crews remained hard at work, sifting through wreckage caused by a wave of powerful tornadoes that swept across the state overnight. The twisters caused major damage to about 60% of Mapleton, a city of about 1,200 residents, Monona County Sheriff Jeff Pratt told reporters Sunday. It was all part of a violent storm system that struck overnight, originating in eastern Nebraska and following a warm front across northern Iowa, according to National Weather Service meteorologist Frank Boksa.