We have Witnessed the Changing Face of Portage Glacier, stable now after long period of receding

Over the past 64 years, the Portage Glacier has undergone profound changes, reflecting the impact of climate change on our environment. Through stunning photos, witness the transformation of this natural wonder and gain a deeper understanding our changing climate. The illustration to the left graced the cover of the Saturday Evening Post in July 1959. Other photos are more recent, showing how far the glacier receded from the parking lot area where cars used to practically park next to it. 

Portage Glacier, in south-central Alaska, is viewed by thousands of visitors annually who come to the U.S. Forest Service Begich, Boggs Visitor Center located on the road system between Anchorage and Whittier. During the past century, the terminus of the glacier has retreated nearly 5 kilometers (little over 3 miles) to its present location in the mountain.

Like other glaciers that terminate in water, such as Columbia Glacier near Valdez or Mendenhall Glacier near Juneau, Portage Glacier has experienced accelerated retreats in recent decades that likely were initially triggered by climate change begun at the end of the Little Ice Age in the mid-1800s. This is seen in recent history primarily by calving at the glacier terminus.   

Portage’s future is complicated. Future changes to the terminus of Portage Glacier will depend on a variety of factors. Present scientific theory suggests that calving glaciers cycle between advance and retreat patterns; with rapid retreats, followed by stable retracted positions, slow advances, and then stable extended positions that are not directly related to climate change. Thus, based on its history to date, and if such a pattern holds for Portage Glacier, the glacier may now be in its stable retracted position and could eventually begin a slow advance.

However, for a glacier to advance, annual net balance—the amount of new snow and ice added to the glacier minus the amount of glacier melt—must be positive. As a rule of thumb for valley glaciers, net balance is positive when annual snow and ice accumulation occurs over more than 60–70 percent of the entire glacier area as it did in the 2023-2024 winter. Such accumulation occurs on the glacier above the end-of-summer snow-line altitude, recently measured by USGS at 1,000 meters in altitude. Only 50 percent (not the rule-of-thumb 60–70 percent) of Portage Glacier is more than 1,000 meters in altitude. (3,280 feet), thus, Portage Glacier may slowly thin and recede rather than experience a slow advance. [1]

 

[1] https://pubs.usgs.gov/fs/2006/3141/

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