 Meanwhile, the earthquakes continued, shifting nearer to the city of Shimabara.On the night of 21 May, two large earthquakes were followed by a collapse of the eastern flank of Mount Unzen's Mayuyama dome, causing a landslide which swept through the city of Shimabara and into Ariake Bay, triggering a great tsunami.It is not known to this day whether the collapse occurred as a result of an eruption of the dome or as a result of the earthquakes.