Why do Natural disaster occur : here you can include the reasons why natural disaster occurs. the reasons could be both man made and natural. i said man made because there is a theory called "Population theory of Malthus " where its stated that if the balance of population exceeds that of food supply many natural disaster would occur. you can google "Population theory of Malthus" for more details. and the natural ones could be earthquakes on which humans have no control. here you can give examples of earthquakes that frequently hits japan.
Advantages of natural disaster:
there are some advantages of natural disaster as well. for example with flood comes lots of silts which in turn makes the soil fertile. apart from that any population that faces natural disaster frequently builds a strong survival mentality. for example some countries in the Indian subcontinent gets hit by hurricane, tornadoes etc yet the destruction rate is very low due to their adoption of the environment.
There are psychological, social, economical disadvantages of natural disasters. Psychological could be that people might loose their loved ones, their hard earned property. social disadvantages could be after effects of the event like you know looting, robbery due to want of basic necessities etc. Economic disadvantages could be the spending to reconstruct the damaged infrastructures, damage of crops, damage of properties etc
then you can include precautionary measures to better deal with natural disaster. So far thats all I can come up with. if anything else comes in my mind I will edit this answer further