Why do arctic rivers in Alaska turn orange?

The Kugururok River located in Noatak National Park, showing traces of an abrupt color change. Credit: Jon O’Donnell, National Park Service.

The wild arctic landscapes ofAlaska are among the most spectacular in the world. Among the state’s towering mountains and icy blue lakes, a huge network of rivers, numbering over 10,000, conveys glacial waters to the Alaskan coast.

These rivers, including the iconic Yukon – the third longest in North America – are known for their abundance of salmon and crystal clear waters. However, in recent years many rivers in the Alaskan Arctic swapped their signature blue color for earthy oranges and yellows.

This color change is fascinating, says Roman Dial, professor of biology and mathematics at theUniversity of Alaska Pacificand it is so striking that some rivers have come to resemble those affected by industrial mining activities.

“It looks like something has been broken or something has been exposed in a way that has never been exposed before,” Dial said. All the hard rock geologists looking at these photos say to themselves: “Oh, that looks like acid mine waste.”

What makes Alaska’s rivers orange?

Professor Dial first noticed changes in the water quality of Alaska’s rivers while doing fieldwork in the Brooks Mountain Range in 2020. Working with a team of graduate students, Dial failed to find adequate drinking water in more than a month of searching.

In fact, some of the polluted rivers studied were so acidic that they could “curdle your powdered milk”. While the water from other rivers remained clear, it was nonetheless often undrinkable, tainted with a strong mineral flavor.

Mont Denali
Alaskan rivers are generally known for their crystal clear waters.

The cause of these “rusty” rivers is not entirely clear. Most of the affected rivers are in remote areas of the state, in protected areas such as the Arctic National Wildlife Refuge or Kobuk Valley National Park.

Therefore, the researchers do not believe direct human activities are responsible, with the orange color coming from the landscape itself.

Climate change could be the culprit

After the discovery of unusual changes in water quality, Professor Dial investigated the matter with a team including Becky Hewitt, professor of environmental studies at theAmherst Collegeand Patrick Sullivan, director of the Institute of Environment and Natural Resources at the University of Alaska Anchorage.

Although they are only in the early stages of studying the issue, their main hypothesis is that climate change could be responsible. Rising temperatures in the region increasingly melts the permafrost, which could release sediments rich in iron and other minerals into waterways.

Iron oxidizes rapidly when exposed to air, taking on a rusty color which could well be the cause. This could also explain the acidification of certain rivers – a process that could pose as yet undetermined problems for aquatic organisms and communities in Alaska.

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