Read the passage. In 79 CE, Mount Vesuvius erupted, burying the city of Pompeii in mud and ash. After investigating, historians found that the volcano was part of a series of events that people had ignored. In 62 CE, Pompeii experienced a large earthquake. After this earthquake, many smaller earthquakes occurred. Based on this, the people of Pompeii should have known that another serious natural event was likely to happen. Even as the volcano started to erupt, people stayed to clean up the falling ash. The eruption completely destroyed the city and killed many people.

What caused historians to think that the eruption of Mount Vesuvius in 79 CE was not the only reason why the residents of Pompeii died?