Canada’s Tweedsmuir Glacier is known to periodically surge, or undergo extended (1-2 year) periods of rapid advance. Geologic evidence suggests that previous surges from Tweedsmuir and Lowell Glaciers have completely blocked the Alsek River, causing formation of large lakes upstream. These ice dams eventually failed sending floodwaters sweeping down to the Gulf of Alaska passing near or through the community of Dry Bay at the mouth of the Alsek.
The current surge began sometime before October 2007 and continued through 2008. Observations by the University of Alaska, Fairbanks showed that the surge advanced the terminus at least 1250 m to the edge of the Alsek River. Considering the possibility of an ice dam event, the National Park Service began monitoring the glacier terminus and the river closely in 2008.
UPDATE: June, 2009
The most recent field observations by the University of Alaska suggest that the current surge has subsided or stalled. The Alsek is freeflowing and eroding the glacier terminus making formation of a dam less likely. The NPS will continue to monitor the Alsek and the Tweedsmuir using aerial surveys, river gauges, remote cameras, and satellite imagery, and will keep park residents and visitors informed of any change in status.
If you need more information or have information to relay, please contact the Glacier Bay Visitor Information Station at 907-697-2627. For recorded information you may also call the Tweedsmuir Glacier Hotline at 907-697-2695.