Ice Flow on Sít’ Tlein

Overlooking the piedmont lobe of Sit' Tlein (Malaspina Glacier). Chris (the helicopter pilot) and Dr. Truffer are installing a timelapse camera to photograph the glacier's motion.

Sít’ Tlein (meaning “Big Glacier” in Tlingit, also known as Malaspina Glacier) is the largest piedmont glacier in the world; it spreads out from the mountains in a wide lobe. The glacier’s ice does not always move at the same speed. Sometimes it “surges,” meaning the ice flows much faster than normal. These surges happen about every 10 years. When they occur, they push ice from the center of the glacier’s lobe out toward the edges.

To understand how the glacier has changed over time, we looked at old science reports, notes from climbing trips, historic photos, and modern satellite data. From these sources, we created a partial history of how Sít’ Tlein has flowed over the past 100 years. We found that during the last 40 years, the glacier moved 1 cubic mile of ice from up-glacier to the lobe each year. If this ice were spread evenly across the whole glacier, it would add about 3 feet of new ice every year. But this is not enough to balance the amount of ice that melts at the surface. According to computer models led by Dr. Brinkerhoff, the glacier is out of balance and is expected to shrink to about half its current size in the next 100 years.

Ice crevasses on the glacier's lobe. During the surge, this usually slow part of the glacier accelerates over a short time. The strain creates fractures on the surface that can fill with water during the summer.

A century of flow and surge history of Sít’ Tlein (Malaspina Glacier), Southeast Alaska

Abstract

Sít’ Tlein (Malaspina Glacier), located in Southeast Alaska, has a complex flow history. This piedmont glacier, the largest in the world, is fed by three main tributaries that all exhibit similar flow patterns, yet with varying surge cycles. The piedmont lobe is dramatically reshaped by surges that occur at approximately decadal timescales. By combining historical accounts with modern remote sensing data, we derive a surge history over the past century. We leverage the Stochastic Matrix Factorization, a novel data analysis and interpolation technique, to process and interpret large datasets of glacier surface velocities. A variant of the Principal Component Analysis allows us to uncover spatial and temporal patterns in ice dynamics. We show that Sít’ Tlein displays a wide range of behaviors, spanning quiescence to surge with seasonal to decadal variations of ice flow direction and magnitude. We find that in the lobe, surges dominate the velocity dataset’s variance (spanning 1984–2021), while seasonal variations represent a much smaller part of the variance. However, despite the regular surge pulses, the glacier lobe is far from equilibrium, and widespread retreat of the glacier is inevitable, even without further climate warming.

Devaux-Chupin, V., M. Truffer, D. Brinkerhoff, M. Fahnestock, M. G. Loso, M. S. Christoffersen, M. Daniel, B. S. Tober, C. Larsen, and J. W. Holt. 2025. A century of flow and surge history of Sít’ Tlein (Malaspina Glacier), Southeast Alaska. Journal of Glaciology 71: e99.

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