Juneau’s Mendenhall Glacier in retreat

JUNEAU, ALASKA — In the mid-1700s Mendenhall Glacier — 12 miles outside of Juneau — began a slow retreat from the Mendenhall Valley. Today, the terminus of the glacier is nearly 2.5 miles from its position nearly three centuries ago.

To get an idea of the scale of the glacier, the black line floating in the lake, near the center of the photo, is a canoe housing roughly 8 human adults.

As the glacier retreats, it exposes new rock surfaces that have not been seen in thousands of years. The bare rock in the photo will take hundreds of years to be recolonized by forests. Moss will first form, followed by alder, spruce, and hemlock trees.

Within the past couple of years, a large chunk of ice broke off from the glacier, leaving pieces of ice floating in Mendenhall Lake. The lake is fed by meltwater from the glacier, and its size has been increasing as the glacier retreats.

The retreat of Mendenhall Glacier is a natural process that has been occurring for thousands of years. But it is also a symptom of climate change. As the Earth’s atmosphere warms, glaciers around the world are melting at an accelerated rate. This is important because glaciers play an important role in regulating the Earth’s climate. They reflect sunlight back into space, helping to keep the planet cool. When glaciers melt, they release more water into the atmosphere, which can lead to further warming.

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