Aug. 16, 2012 — -- A 400-foot deep sinkhole in Louisiana is expanding and today swallowed the boat of two cleanup workers who had to be rescued from the hole. Officials are still fearful of the possibility of explosions from nearby gas-filled caverns.
"It has expanded 50 feet and during that expansion there were workers that were working on the cleanup of the diesel," Kim Torres, spokeswoman for the Office of Emergency Preparedness, told ABCNews.com today.
The two workers were in a boat tied to a tree when the area where the tree grew fell into the sinkhole.
The workers were rescued by airboat. They were uninjured but their boat disappeared into the sinkhole. The cleanup process has been halted.
The gaping hole measures about 526 feet from northeast to southwest and 640 feet from northwest to southeast. It is in Assumption Parish, La., about 50 miles south of Baton Rouge.
The sinkhole sits in the middle of a heavily wooded space where it has consumed all of the soaring cypress trees that had been there. Flyover photos show some of the treetops still visible through the mud.
Authorities enacted a mandatory evacuation for residents of about 150 homes in the area. Last week, Torres said that most residents chose to stay in their homes. But as of today, 60 percent of those homes have been evacuated even though the mandatory evacuation order was not escalated to a forced evacuation, when authorities remove residents.
"I think everyone realized it was serious even though they felt it was contained [before]," Torres said. "When you put human lives in...it just becomes more serious and maybe people are heeding the warning a little bit more."
Torres said she expects that the 60 percent will increase after the incident with the cleanup workers.
While officials are not certain what caused the massive sinkhole, they believe it may be have been related to a nearby salt cavern owned by the Texas Brine Company.
After being used for nearly 30 years, the cavern was plugged in 2011 and officials believe the integrity of the cavern may have somehow been compromised, leading to the sinkhole.
Louisiana's Department of Natural Resources required that Texas Brine drill a well to investigate the salt cavern as soon as possible, obtain samples from the cavern and provide daily reports on the findings.
The sinkhole is on the outside edge of the salt dome where this particular brine well is located.
"There are some indications that it very well may have been connected, but there's just indications," Texas Brine Company spokesman Sonny Cranch told ABCNews.com. "There's nothing concrete that has connected the sinkhole to the cavern."
The exploratory rig is being assembled but parts of it are still being shipped. It could take 40 days for the actual drilling to begin, even with an expedited process, Torres said.
In the meantime, officials and residents are left to worry about the possibility of an explosion.
All of the neighboring natural gas pipelines that were of concern last week have been depressurized and emptied, but the nearby caverns are still causing concern.
One cavern that contains 940,000 gallons of butane is of particular concern, Torres said. It's about 2,000 feet from the sinkhole.
Authorities are concerned about the massive explosion that could result from the butane's release to the surface if the sinkhole were to expand far enough to reach it.
There was bubbling in the water and the sinkhole is near areas where there has been exploration for oil and gas in the past. This would make the presence of low levels of naturally occurring radioactive material (NORM) possible.
The state's Department of Environmental Quality said water samples from the sinkhole showed oil and diesel fuel on its surface, but readings have not detected any dangerous levels of radiation.
"It's not going to get fixed tomorrow," Torres said. "We urge the residents to leave to protect themselves. We have no idea how far this sinkhole will expand or in what direction. We have no clue."