From the Wikipedia page:
Boomtowns are typically characterized as “overnight expansions” in both population and money as people stream into the community for high-paying jobs, mining prospects, attractive amenities or climate, or other opportunities. Typically, newcomers are drawn by high salaries; meanwhile, numerous indirect businesses develop to cater to workers often eager to spend their large paychecks. Often, boomtowns are the site of both economic prosperity and social disruption as the local culture and infrastructure struggles to accommodate the waves of new residents. General problems associated with this fast growth can include: doctor shortages, inadequate medical and/or educational facilities, housing shortages, sewage disposal problems, and a lack of recreational activities for new residents. 
The University of Denver separates problems associated with a mining-specific boomtown into 3 categories: 1) deteriorating quality of life, as growth in basic industry outruns the local service sector’s ability to provide housing, health services, schooling, retailing and urban services; 2) declining industrial productivity in mining because of labor turnover, labor shortages, and declining productivity; and 3) an underserving by the local service sector in goods and services because capital investment in this sector does not build up adequately.   The initial increasing population in Perth, Australia (considered to be a modern-day boomtown) gave rise to overcrowding of residential accommodation as well as squatter populations.  “The real future of Perth is not in Perth’s hands but in Melbourne and London where Rio Tinto and BHP Billiton run their organizations”, indicating that some boomtowns’ growth and sustainability are controlled by an outside entity. 
Boomtowns are typically extremely dependent on the single activity or resource that is causing the boom (e.g. nearby mine, mill or resort), and when the resources are depleted or the resource economy undergoes a “bust” (e.g. catastrophic resource price collapse), boomtowns can often decrease in size as fast as they initially grew. Sometimes, all or nearly the entire population can desert the town, resulting in a ghost town.
This can often be on a planned basis. Mining companies nowadays will create a temporary community to service a mine-site, building all the accommodation shops and services, and then remove it as the resource is worked out.