Explain how the moon is causing volcanic eruptions

All the disasters in this story are caused by one event: an asteroid hitting the moon. The asteroid is denser than expected, and so has a bigger impact on the moon than expected. The observers notice that when it hits, the whole moon seems to move closer to the Earth. This is exactly what has happened, because the asteroid knocked the moon into a closer orbit. The moon's gravitational pull therefore increases, causing all sorts of natural disasters like tsunamis, earthquakes and volcanic eruptions. In this story, the moon goes from being something familiar to something sinister.