Economic activity shifting elsewhere
Ghost towns may result when the single activity or resource that created a boomtown (e.g., nearby mine, mill or resort) is depleted or the resource economy undergoes a “bust” (e.g., catastrophic resource price collapse). Sometimes the town might cease to officially exist, but the physical infrastructure remains.
Human intervention
Railroads and roads bypassing or no longer reaching a town. River re-routing is another factor. Some towns become deserted when their populations are massacred. Ghost towns may be created when land is expropriated by a government. Sometimes the town might cease to officially exist, but the physical infrastructure remains.
Disasters, actual and anticipated
Natural and man-made disasters.
Disease and contamination
Significant fatality rates from epidemics. Catastrophic environmental damage caused by long-term contamination.