Weather Almanac for April 2000

Betting On A Breakup
The Nenana Ice Classic

While most of us south of the Arctic Circle spend April preparing or planting our gardens, the residents of the Far North await the signs that winter is at last over for another year. One of the most notable Spring events in these northern lands is the breakup of the ice cover on the local river.

Nenana, Alaska Location

In the small village of Nenana, Alaska, located 88 km (55 miles) southwest of Fairbanks and approximately halfway between that city and Denali National Park, the breakup of ice on the Tanana River has been the focus of particular attention for the past 83 years, an event known as the Nenana Ice Classic.

Nenana, Alaska Location

The Tanana River is born in the ice fields of the eastern Alaska Range near Mt Hayes. Initially, its waters flow northward towards Fairbanks, there turning southwestward. At the village of Nenana, the Tanana River meets the Nenana River which flows northward from the Alaska Range near Denali. At this junction, the waters join and again flow northward to the Yukon River, meeting it at the town of Tanana. The Village of Nenana is on the south bank of the Tanana River, just east of the mouth of the Nenana River.

Because river travel had long been the best and fastest mode of transportation in interior Alaska before air travel, the breakup of river ice meant that people and goods could again easily be moved over long distances. For example, in the years from 1933 to 1948, the wood-burning stern-wheeler Nenana plied the waters of the Tanana and Yukon Rivers carrying goods and supplies from the rail line into the Alaskan interior.

(In 1925, when a diphtheria epidemic threatened the town of Nome, the much needed serum was raced from the rail line at Nenana to Nome by dog team. Twenty teams relayed the medicine 674 miles (1084 km) across the frozen terrain in 27.5 hours! Today this historic event is commemorated with the world-famous Iditarod Sled Dog Race.)

In 1906, a group of engineers were building a bridge across the Tanana River for the Alaska Railroad. To pass the time, they decided to bet on the date of the breakup if the river. Railroad workers continued the wagering once the line between Fairbanks and Anchorage was completed. In 1917, they got 800 people to ante up a dollar each for their guess, and Nenana Ice Classic was born. In 1917 the ice went out at 11:30 am on April 30. The first co-winners, who guessed closest to the actual time, were Frank O. Jones and Andrew Hoye. They split the purse of about $500.

Nenana Ice Classic Tripod On River Photo Courtesy:Nenana Ice Classic

Since that date, local residents have annually wagered on the exact date and time of the breakup of the river ice just north of the junction between the Tanana River and the Nenana River. As word of the wagering spread across Alaska, more non-locals became involved. Today, over a quarter million bets come in, not only from across the State but from around the world making the Nenana Ice Classic an international event.

The Tanana River usually freezes over during October and November, the ice thickening to an average of 42 inches near Nenana by early April. When the grip of winter is finally released, the ice begins to melt from above as the air temperatures rise above the freezing mark. Ice is also removed by melting and erosion from below as the waters beneath the ice once again flow from upriver.

Breakup on a river can be gradual as occurs in years when the ice slowly melts until the surface ice weakens to the point it cannot sustain a complete ice cover. Gradual breakups generally occur with a warm early spring.

Breakup may also occur suddenly when warm weather is delayed until late spring and melting proceeds rapidly. A rapid increase in melt water along the river system can cause flooding, particularly if large chunks of ice produce ice jams and dams which halt and backup the water flow.

Tanana River After Breakup 1998 Photo Courtesy: Nenana Ice Classic

The breakup of the Tanana River near Nenana has occurred between April 20 and May 20 during the 1917-99 period over which the Ice Classic wagering has taken place. The most likely time from a statistical analysis of the data appears to be in the early afternoon of May 6, between 1 and 2 pm (AST).

The Nenana Ice Classic, a state- and federal-regulated game of chance, now requires a wager of $2 be placed on the exact minute and date of the breakup of the Tanana River. For the purposes of determining the winner, breakup is defined as the exact moment a "tripod" set in the river ice moves more than 100 feet downriver.

Wagering opens in early February and closes in early April. The Nenana Ice Classic employs 85 to 100 of the citizens of this village of 450, most registering the quarter million or so wagers submitted. Half of the money collected goes to the winner(s), the remainder after expenses goes for community causes such as the library and school.

Nenana Ice Classic Tripod Photo Courtesy: Nenana Ice Classic

The determination of the exact time of the breakup is, in itself, a marvel of Alaskan ingenuity. During the last weekend of February, a wooden tripod is sent into the river ice. (A part of the overall Nenana Ice Classic festivities, this weekend is known as Tripod Weekend.) The tripod, actually a tower with four legs, supports a central flagpole connected to a clock on shore. Its legs are cut from local spruce trees that are stripped of their bark and painted with black and white stripes for visibility against the river ice.

On Tripod Weekend, four holes are cut into the river ice and a tripod pole inserted into each hole. Water rising through these holes quickly freezes, cementing the legs solidly in place. The central flagpole is later connected to a timing device located onshore in such a way that once the tripod moves further than 100 feet from its initial position, the clock is stopped, thus indicating the winning time.

Nenana Ice Classic Tripod Photo Courtesy: Nenana Ice Classic

Once the river ice reaches the stage it becomes unsafe to walk on, a wire is attached to the rope that runs from the top of the tripod to an ingenious mechanism located in a watchman's tower on shore. When the ice finally breaks and the tripod begins to move, the rope raises a 50-gallon drum of rocks to the top of the tower. The action then trips another line releasing a guillotine that cuts the main rope to the tripod. When this rope is cut, two other ropes are tripped: one that stops the clock and another that sets off a loud siren, alerting the town that the end of the wait has come. Once activated, watchmen are posted to ensure no one tampers with the setup. Now the serious waiting begins.

Generally the ice on the Nenana River downstream of the tripod breaks up first. This allows room for the Tanana River ice below the tripod room to move downstream. About a week later, the Tanana ice will usually give way and the tower begins to more. When the first signs of ice movement are detected, a local siren calls townsfolk out to witness the official breakup.

The breakup can be an exciting event in those years that breakup is swift and releases huge slabs of ice that twist and crunch against each other. There have been reports of large chunks of ice thrown ashore at breakup and stories of flying ice breaking windshields of vehicles parked near the riverbank.

Nenana Ice Classic Clock Photo Courtesy: Nenana Ice Classic

With the stoppage of the clock, the Nenana Ice Classic result is determined and it is "officially" springtime in this corner of Alaska. In 1999, the winning time/date was 9:47 pm (AST) on April 29. I'll let you know this year's result once I hear them.

The ice has broken: May 1 at 10:47am is the official breakup time for the 2000 Ice Classic. There were 18 winning tickets to split a total payoff of $335,000.

An interesting sidebar to the Nenana Ice Classic story is that the fairly long and precise record of river breakup has been used by climatologists to understand climate change in the area. Forecasts of global warming indicate that polar regions should warm more quickly than at lower latitudes. Earlier winning dates for the Nenana Ice Classic in the future could help confirm these forecasts.

Ice Break-up On Tanana River Photo Courtesy: Nenana Ice Classic

For more on the Nenana Ice Classic, visit their website .

Written by
Keith C. Heidorn, PhD, THE WEATHER DOCTOR,
April 15, 2000

The Weather Doctor's Weather Almanac Betting On A Breakup: The Nenana Ice Classic
©2000, Keith C. Heidorn, PhD. All Rights Reserved.
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