The differences among hazards, disasters and catastrophes are pretty straight forward. Basically, a natural hazard is a natural process of the earth, like a volcano. Magma bubbles up at a plate boundary and BLAM you have a volcano which only gets labelled as a hazard depending on how it will affect humans. So if you build your village at the base of a mountain and it begins to ooze a slow basaltic lava flow which encroaches on your village borders, it simultaneously becomes known as both a volcano and a hazard. A natural hazard can become a disaster when it fulfills the following criteria:

- It kills ten or more people
- It affects or displaces 100 or more people
- International assistance is requested
- A state of emergency is declared

Furthermore, a disaster occurs over a limited period of time. A disaster may escalate to a catastrophe if an organization providing assistance does a heck of a job, causing more issues and making it more difficult for the civilization to recover. A catastrophe has all of the same criteria except that it usually occurs over an extended period of time. Years can pass before the aftermath of a catastrophe is rectified or the people affected recuperate. To recap:

Hazards: are natural occurrences on earth which become exacerbated and dangerous when humans get too close.
Disasters: Hazards which severely affect nearby humans for a short period of time and which can often cause death and general mayhem.
Catastrophes: HUGE disasters which not only cause numerous deaths and structural damage in the onset but which also take for-ever to recover from and often continue to cause death and mayhem for years after the initial event.