Complex sentence: The east flank of the Mayuyama dome collapsed unexpectedly following a post-eruption earthquake, creating a landslide, causing a megatsunami that reached a height of 330 ft (100 metres), and killed an estimated 15,000 people.
Split into simpler sentences: The east flank of the Mayuyama dome collapsed unexpectedly following a post-eruption earthquake, creating a landslide. This caused a megatsunami that reached a height of 330 ft (100 metres), and killed an estimated 15,000 people.