Records have been recorded since 1917 of the breakup of river ice in the Tanana River at the town of Nenana in central Alaska. A tripod is placed near the middle of the river each winter opposite the town wharf and the date and time of its collapse is recorded.
Details of the “Nenana Ice Classic”, where people estimate the date and time of the next breakup can be found at: www.nenanaakiceclassic.com/ This website also contains a lot of data about historical ice breakups since 1917. A webcam, updated every 30 minutes, is at: http://www.wunderground.com
The Tanana River (about 940 km or 580 miles long) is a major tributary of the Yukon River in central Alaska, north of the Alaska Range. Its headwaters are near the Alaska-Yukon border from where it flows in a generally westerly direction, passing south of the city of Fairbanks. About 80 km (55 miles) downstream of Fairbanks is the town of Nenana and the Nenana River tributary.
The Tanana River freezes over in about December and typically achieves an ice thickness at Nenana of 40-50 inches (1-1.2 m) by early April. The collapse of the river ice (known as the “breakup”) typically occurs in late April or early May. The breakup usually occurs quite suddenly during the spring thaw and the resulting high river flows. The majority (80%) of breakups occur in the daytime between 9 am and 8 pm.
This post analyses the variation in the date of breakup since 1917. It also presents the variation in ice thickness in each year since 1989 and its relation to the date of river breakup.
ANNUAL BREAKUP TREND
BREAKUP IN INDIVIDUAL YEARS
The dates of the annual breakup at Nenana have decreased by about seven days over the past century. However this decrease has not been uniform. Between 1917 and 1970 the average breakup date was 6 May, but since 1970 the average breakup date has been 2 May. This decrease may be due to warmer winters over the past century, although development of the Fairbanks region since 1970 may also have had an influence. Or maybe the Spring temperatures or rainfall have changed over the past century – I must check that out sometime!
The date of the breakup is almost independent of the maximum thickness of ice during the winter. During the past 27 years, since 1989, the breakup generally occurs (80% of the time) between 28 April and 12 May irrespective of how cold the preceding winter has been. It therefore is suggested that the breakup date is mainly dependent on the rising temperatures in spring (which causes snowmelt) and spring rainfall (which increases the snowmelt and can also produce floods and ice-jams in the rivers).
THE 2016 BREAKUP
My estimate of the date of the 2016 breakup is 28 April at 2:06 pm. But, realistically, the breakup could be a week or more either way from this. Lets wait and see – not much longer to go now!
Permission to publish the “2016 Poster” and the webcam image was kindly granted by the Nenana Ice Classic organisation. The “2016 Poster” is the work of Alaskan artist Barbara Lavallee. The webcam image is from an installation of Borealis Broadband using a camera provided by TecPro.
This article was written by Brian Gunter Narooma, NSW. In his previous life Brian was an engineering hydrologist involved over many years in the analysis of rainfall and river flow of data for the planning of major water resources projects in Australia, Asia and Africa. In recent years he has been one of the Marine Rescue NSW (previously Royal Volunteer Coastal Patrol) volunteer weather observers who operate the Narooma station for the Bureau of Meteorology.