Denali’s Muldrow Glacier Currently Experiencing an Historic Surge Event

In a prior surge event during the winter of 1956-57, the glacier advanced just over 4 miles in a few months’ time. Today, preliminary satellite radar image analysis of the Muldrow Glacier completed by UAF researchers Mark Fahnestock and Bretwood Higman suggests it is currently flowing at a rate of 10-20 meters, or 30-60 feet, per day which is about 100 times faster than normal. 

This surge is believed to have begun sometime in January and is expected to continue for several months.  

Scientists had been anticipating this surge for a while now, as the glacier displays evidence of a 50-year surge cycle, but no one knew exactly when it would occur. Adema, who has studied the Muldrow Glacier for decades, is particularly interested in investigating this event more closely, “I’ve been waiting for the Muldrow to surge for a long time. This is an incredibly exciting event to witness and to study!”  

The current surge of the Muldrow Glacier is likely not driven by impacts of climate change, but rather by the glacier’s geomorphology, the unique nature of the structure and composition of the glacier’s ice, its surrounding rocks, and the topography it is moving through.   

Surges like this may be caused by the interplay of ice buildup at higher elevations over time, and supply of meltwater to the base of a glacier. Due to the geometry of many surge type glaciers, ice accumulates and thickens on the upper glacier over many decades with only a slow flow or transfer of ice to the lower glacier. At some point during the quiet, accumulation phase, the mass reaches a threshold where the internal hydrology of the glacier is disrupted. Rather than running out at the terminus, meltwater is retained at the base of the glacier.

The soft metamorphic bedrock that underlies the Muldrow, along with the massive quantities of retained water reduces friction and “floats” the glacier causing it to surge. Once a surge begins, positive feedback loops and momentum can often contribute to the speed and duration of the surge. 

“The fact that it’s happening in a place that people know and care about makes it rather interesting,” says Adema.

Overall, while it is estimated that only one percent of all the world’s glaciers ever surge, Adema points out that Denali is a bit unique in this respect. “A relatively large portion of Denali glaciers are surge type due to the dramatic relief of the mountain. The intermittent surging makes these glacier less ideal for monitoring the impacts of climate change, but are fascinating to watch when surges like this occur.”

Park scientists will continue to monitor and map this dynamic situation both during and after the surge event, with the hope of increasing our understanding of how glaciers in Alaska are changing. The NPS also monitors the mass balance of a small set of glaciers in several national parks. Non surge type glacier dynamics are a long-term indicator of climate change. On the south side of Denali, opposite from the Muldrow, the Kahiltna glacier is a long-term index glacier which is slowly retreating. Overall, ice cover in Denali has declined by 8 percent since 1952.

Visitors to Denali National Park this summer should temper expectations of what they may be able to see without a backcountry excursion or overflight, however. Evidence of this surge is likely to be less dramatic when viewed from the Park Road or the Eielson Visitor Center, with only a bit more jumbled ice visible in the distance along the edge of the glacier.

More information on the surging Muldrow Glacier can be found at go.nps.gov/MuldrowGlacier.