How did the mariners know that Jonah was the cause of their problem?
The mariners knew that Jonah was the cause of their problem because they cast lots to determine who was responsible for the storm that was threatening their ship. The lots indicated that Jonah was the one who had brought God's wrath upon them, and Jonah admitted to the mariners that he was fleeing from God's command to go to Nineveh. This revelation made it clear to the mariners that Jonah's disobedience to God was the cause of the storm, and they asked him what they should do to calm the sea. This ultimately led to Jonah being thrown overboard and swallowed by a great fish, as he knew that this was the only way to save the mariners' lives and atone for his disobedience.