A hazard is a natural event that could potentially hurt or kill people and damage property.  A disaster is a hazardous event that takes place within a limited time span and a defined area.  For a disaster to occur 10 or more people are killed, 100 or more people are affected, a state of  emergency is declared and international assistance is requested.  A catastrophe is a huge disaster that costs a huge amount of money and takes years for recovery to take place.  Hurricane Katrina in New Orleans is an example of a catastrophe.