I know what you're thinking. So, someone in Alaska sits at the river and waits for it to break? Well actually it's a bit more modern than that. The exact time is determined by a tripod apparatus placed in the middle of the frozen river. The tripod has a trip wire that is disturbed when the ice breaks. This sounds a bell, cuts the tripod rope and stops the clock.
The information above was told to me by a supervisor at my job. In order to check spelling I googled the Nenana Ice Classic and found that it has it's own website (includes a ton of pics) which I will post the link to below. In addition, I found a times article about the event. The article isn't of particular interest but the date it was published is: Monday May 18, 1959. A reporter wrote about the Classic 52 years ago yesterday, just like I'm doing today. Only the writer didn't have internet to verify the facts or make a blog post. Interesting I think.
Heres the Time link: http://www.time.com/time/magazine/article/0,9171,869038,00.html
Heres the Classice page link: http://www.nenanaakiceclassic.com/
Alaska Word: Three dog night- It's so cold that two dogs just aren't keeping you warm enough.