. >> reporter: willston north dakota is a boom town.per scrambled to build new homes, thousands of transient workers, mostly men, are housed in camps. in december the city council closed the two strip clubs after beating deaths. rents rocketed. with oil selling below $50 a barrel low prices are now putting the breaks on the boom. once eager retailers are starting to reconsider. >> with oil prices down people will start thinking maybe this isn't such the real deal and it is going to go away like it has in the past. which i don't think that is going to happen. i think it will rebound. i think we'll be around an industry that will support us for at least 40 years. >> reporter: just four years ago willston was an agricultural town of 12,000. since then it has tripled in size. now with buildings still going up from the oil boom comes the oil slump. newspaper headlines now speak of job cuts. so far the slow down has fallen short of an oil bust. at willston state college, the staff has grown 8 fold. the students remain confident. >> i'm going

kerry sanders is in willston florida. he went underground into a sinkhole. there you are.vil's den and they got that name because when early settlers came here all they could see was the steam rising up through that hole in the ground out there. they thought it must be the devil's breath. today with scientific teams from pbs's noef a we have a much better understanding of sinkholes. when a sinkhole begins to open it is often dramatic swallowing entire buildings or as was the case in the louisiana bayou, an unbelievable sight. a stand of 40-foot cypress trees gone within seconds. nova on pbs examines these events in their sinkholes, sinkholes, buried alive. >> trying to get to my brother. i thought i could hear him yelling and screaming to help. >> they occur around the world, but geologists believe there more in florida than anywhere else on earth. we joined nova. at devil's den for a rare look deep inside a sinkhole. >> this is an example. what used to be the floor of the ocean, believe it or not. >> sinkholes develop when lime stone is soaked by rain. thousands of years