BAYOU CORNE, La. — It was nearly 16 months ago that Dennis P. Landry and his wife, Pat, on a leisurely cruise in their Starcraft pontoon boat, first noticed a froth of bubbles issuing from the depths of Bayou Corne, an idyllic, cypress-draped stream that meanders through swampy southern Louisiana. They figured it was a leaky gas pipeline. So did everyone else.

Just over two months later, in the predawn blackness of Aug. 3, 2012, the earth opened up — a voracious maw 325 feet across and hundreds of feet deep, swallowing 100-foot trees, guzzling water from adjacent swamps and belching methane from a thousand feet or more beneath the surface.

“I think I caught a glimpse of hell in it,” Mr. Landry said.

Since then, almost nothing here has been the same.

More than a year after it appeared, the Bayou Corne sinkhole is about 25 acres and still growing, almost as big as 20 football fields, lazily biting off chunks of forest and creeping hungrily toward an earthen berm built to contain its oily waters. It has its own Facebook page and its own groupies, conspiracy theorists who insist the pit is somehow linked to the Gulf of Mexico 50 miles south and the earthquake-prone New Madrid fault 450 miles north. It has confounded geologists who have struggled to explain this scar in the earth.