Honestly, I could probably do an entire series on natural disasters. They come in all varieties. Hurricanes, tornadoes, mudslides, avalanches, earthquakes, droughts, blights...the list is endless.
While the disasters themselves are, well, disastrous, sometimes the aftermath is what causes more trouble for the people involved. For example, flooding following a hurricane can cause sanitation breakdown, which in turn can create a breeding ground for disease. Or, fires after an earthquake can add to the confusion and devastation.
There's also the issue of what to do with survivors. Relocation and rebuilding processes can take years. The economy of the region could be set back several years and many businesses may never return. Fear of another similar disaster could dissuade residents from returning. Or, depending on the type of disaster, the region may become completely uninhabitable.
How can you leverage natural disasters and their aftereffects in your book?
What disasters occur in your world? How do they differ by geographical region? How frequent are disasters? What changes in lifestyle or architecture have people made in order to minimize the effects of cataclysmic events? (Examples: storm cellars in tornado alley, evacuation routes in hurricane-prone areas, "earthquake proof" buildings).
Do disasters occur on a regular basis? Is there any way to predict them? What events lead up to each disaster? Are there certain seasons where disasters are more likely?
What response teams are in place for after a disaster? Is there something similar to FEMA that steps in to provide aid for survivors, or are they left on their own?
How are natural disasters viewed? If you're writing fantasy, do people believe that deities are responsible for the disaster? If so, what steps might they take in an attempt to prevent another disaster from occurring? (The Kinsman Chronicles by Jill Williamson and Legends of Karac Tor by D. Barkley Briggs provide some good examples of this.)
What problems occur after a certain type of disaster? Are there steps to prevent disease from spreading? Do people tend to move out of disaster-stricken areas, or do they stay in their homes? What motivates their decision? (Example: some civilizations would continue to settle on volcano slopes, since the soil was very fertile).
How do natural disasters provide motivation, barriers, or opportunities for your characters?
What natural disasters are likely in your area? How do you prepare?
What natural disaster are you most proud of incorporating into your book? Did you create any new types of disaster for your book?