Modifiers matching calamity:

• natural,
• unforeseen,
• serious,
• violent,
• massive,
• world,
• physical,
• devastating,
• international,
• national,
• widespread,
• common,
• marine,
• destructive,
• sudden,
• terrible,
• political,
• financial,
• major,
• unfortunate,
• environmental,
• unforeseeable,
• public,

Simple categories matching unforeseeable:

• reason,
• situation,
• thing,
• event,
• contingency,
• condition,
• catastrophe,
• incident,
• calamity,
• risk,
• cause,
• inactivity,
• circumstances,
• occurrence,
• development,
• disaster,
• change,
• setback,
• circumstance,
• disturbance,