听力原文： A Russian cargo ship with about 30 crew members aboard was in danger of sinking off Russia's eastern coast while stormy weather interfered with rescue efforts, state-run Itar-Tass news agency said Friday. Ice had formed on the outside of the ship, and the crew was chipping it off. The crew sent out a distress signal, but there was no explanation of the problem23. Because of the severe weather, aircraft can't be used to rescue the crew. According to Itar-Tass, the vessel is about 90 miles from an oil rig where rescue vessels are based, while a tugboat dispatched from land was still about four times farther away24. The cargo ship had been en route to a fishing area when it experienced problems, the news agency reported. The ship hauls fish from boats to ports. The Russian cargo ship was sinking. What was the direct cause?