Sít’ Tlein (Malaspina Glacier): Is the World's Largest Piedmont Glacier at Risk?

By Kitsel Lusted, University of Alaska Fairbanks.

Sít’ Tlein (Malaspina Glacier), circled, lies near Yakutat in Wrangell-St. Elias National Park and Preserve. NPS.

Alaska's glaciers are changing. They are thinning by an average of three feet a year and add significantly to global sea level rise, with big consequences for ecosystems and people worldwide.

The big glacier

Sít’ Tlein — Tlingit for "big glacier" — is the traditional name of what has recently been called Malaspina Glacier, on the coast of Wrangell-St. Elias National Park and Preserve near the community of Yakutat. It is the largest piedmont glacier in the world.

A piedmont glacier spills out of the mountains and spreads across the lowland below in a vast fan. Sít’ Tlein fans out like an icy delta at the foot of the St. Elias Mountains — blue, huge and old, with lakes lapping at its front and full-grown forests on top of its ice cliffs. Its ice volume is so great that melting it all could raise sea level measurably, and earlier studies showed it is thinning fast — faster than the average Alaskan glacier.

A moraine, and the sea behind it

• A large raised moraine, left by an old surge, runs round the glacier's edge. It may explain why Sít’ Tlein has stayed where it is so long, while its tidewater neighbours retreated and left Icy Bay and Yakutat Bay behind.
• Glaciers that end in the sea have retreated rapidly all over Alaska in recent decades, because sea water — warm compared with ice — is a powerful melting force.
• Most of Sít’ Tlein ends against the moraine or in lakes in front of it. But recent measurements show that the largest, Sitkagi Lagoon, is almost as salty as the ocean — so the glacier is definitely in contact with warm sea water. The new lakes have exposed it to the ocean and are speeding its retreat.

The research

Scientists from the University of Alaska Fairbanks, the National Park Service, the University of Arizona and the University of Montana, funded by the National Science Foundation and the NPS, have studied Sít’ Tlein for the past two years. Their main question: is it at risk of rapid retreat? Using airborne radar and seismic sounding, they are asking:

• Thinning and retreat. The glacier is known to be thinning and retreating — but how fast are these changes developing?
• Lakes. The lakes around it are new and growing. How will they change the way the glacier behaves?

The 2023 field team — Michael Daniel, Martin Truffer, Doug Brinkerhoff, Mikaila Mannello, Victor Devaux-Chupin and Annegret Pohle — focused on the processes at work on the upper glacier. In April 2023 the researchers visited Yakutat to present the project; the 30-minute talk is on YouTube (https://youtu.be/Y0Qc7GiScig).

The lead scientist is Martin Truffer of the University of Alaska Fairbanks; the NPS contact is geologist Michael Loso.

Sources

• National Park Service, Wrangell-St. Elias National Park and Preserve, "Sít’ Tlein (Malaspina Glacier) Research," by Kitsel Lusted, University of Alaska Fairbanks. https://www.nps.gov/articles/000/s%C3%ADt-tlein-malaspina-glacier-research.htm
• The original's aerial photograph of the glacier carries no credit and is not reproduced here.
• Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.