FAIRBANKS — The approaching spring and the current warming weather will cause Alaskans to get outside more. And some people will no doubt venture onto the still-frozen lakes and rivers.

So it’s good to know a bit about ice thickness and how much weight a frozen surface can support. The Alaska Department of Fish and Game has the following guidelines:

Two inches can support one person on foot; 3 inches can support a group walking in single file; 8 inches can support a vehicle of 2 tons gross weight; 12 inches can support a heavy truck; 25 inches can support 45 tons; 36 inches can support 110 tons.

Remember that ice thickness isn’t uniform. A frozen surface might be thick in some places but thin in others on the same pond, lake or river.

One of the most-watched ice thickness measurements, however, is of the ice on the Tanana River at Nenana. That’s because the location is the site of the Nenana Ice Classic, the annual guessing game that lately has had a prize of about $300,000 that is split among the tickets whose purchasers guess the date and time that the river breaks up.

The deadline to purchase the $2.50 tickets is Wednesday. The winner or winners will be paid June 1.

The tripod — it actually has four legs — was assembled on the river March 5. The structure will be connected to a timer on shore. The timer stops, marking the official breakup time, when the tripod moves 100 feet downstream.

Ice thickness measurements on the Tanana River this month were fairly constant in March: 39.7 inches on Thursday, 36.3 inches on March 23, 39.5 inches on March 16 and 38 inches on March 5.

Historically, the Tanana River breakup has occurred between April 20 and May 20.

 Here are some ice thicknesses elsewhere in the region Thursday, as provided by Ed Plumb, acting senior service hydrologist with the National Weather Service in Fairbanks:

Birch Lake: 36 inches

Salcha River: 25 inches

Chena Lakes: 32 inches

Twin Bears Camp: 28 inches

Chena at Steese Highway: 22 inches

Olnes Pond: 29 inches

Smith Lake: 32 inches

Tanana River at Chena Pump  Road: 34 inches

Chena River at Pikes Landing: Some open water; unsafe for measurement.

Contact the newsroom at 459-7572.