Answer: Earthquakes

The length of a day seems like a fixed value, being determined by the length of time the planet rotates. Surely no natural disaster could change the Earth to the point that it changes its rotation?

While such a change is beyond the power of lesser natural disasters like still-formidable hurricanes, there is one natural disaster with the power to change the length of a day: high-magnitude earthquakes. A recent example of one such event was the massive 8.9 magnitude earthquake that struck northeastern Japan in the spring of 2011.

The amount of mass moved by the Japanese earthquake was so vast that it actually 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.

What does that kind of shift look like when taken out of the context of time and put into the context of physical space? The 2011 earthquake was so powerful that it moved Japan’s main island by about 8 feet and shifted the figure axis of the Earth by around 6.5 inches (17 centimeters).