We do have environment objects. I believe rockfall is already implemented as an environment object; earthquakes, volcanoes, etc. could become environment objects, too. The "earthquake object" can be the same as the environment object, so we don't need two objects for each disaster.

The advantage of an object based approach is that you can have a nice list, including pictures and descriptions, of available/activated environment objects.

The disadvantage is that we do not have parameters associated with each disaster (except by activating it multiple times). But that's something we need to implement anyway for environment objects (e.g. "amount of rockfall?"), game goals (e.g. "which buildings need to be built?") and rules ("how many relaunches? relaunch cost?").