Which one of these events could potentially change the length of the day?
The length of a day is determined by the rotation of the planet. Among the four events listed, an earthquake of sufficient magnitude could do this; the others cannot. A recent example of is the earthquake that struck northeastern Japan in 2011. The amount of mass moved by the earthquake was so large that it shifted parts of Japan by about 4 metres, moved the figure axis of the Earth by about 17 centimetres and accelerated the rotation of the Earth. As a result of the mass shift and the acceleration that followed, the length of an Earth day was shortened by 1.8 microseconds.