Cash floe

Every spring, the residents of Nenana, Alaska -- about an hour’s drive from Fairbanks -- play a heated game of chance by placing $2.50 bets on the precise moment when ice on the nearby Tanana River will break up. A giant spruce tripod embedded in the river’s thick ice acts as a marker: When the tripod floats away, a winner is declared. The first Nenana Ice Classic jackpot in 1917 paid out $800, and tickets sold for a dollar. Last year, six people accurately predicted the winning time -- 2:16 p.m. April 24 -- to split a $301,000 jackpot. Here’s how the berg carves out its Vegas-on-ice routine.

March 6: A pole with three supports is painted black and white and decorated with colorful flags to make sure it is visible against the white-on-white landscape. The structure is frozen in place by digging a 2-foot trench into the ice then flooding it with water.

March 31: The ice on the river measures 36 inches thick, probably due to a four-week cold snap that started in January when temperatures hovered between 40 and 55 degrees below zero.

March-April: Betting begins. Because online betting is illegal, way-out-of-towners call in their bets and send money orders or checks to secure a ticket.

Today: Ticket sales end. River-watchers start looking for holes in the ice or water pooling on the surface, signs that the thaw is underway.

This week: If melting continues, organizers hook up a clock to the tripod to record an accurate time. A guard is posted at the site 24/7 to make sure no one tampers with the tripod or the clock.

The big break: The tripod has to move 100 feet for the breakup to be official.

-- Mary Forgione