If you’re excited for a Disney story of fluffy green mice, I’m sorry to disappoint you. ‘Glacier mice’ are not mice–or animals at all. But, if you like science, read on.
If It’s Not A Mouse, What Are Glacier Mice?
On the glaciers, occasionally a gathering of debris forms. It could be dust, or it could be a small pebble. Whatever it is, it’s our little mouse’s ‘heart.’ After a period of time, this clump starts growing moss. Then, the wind pushes these little balls around, and eventually, all sides become covered in moss. In 1951, Dr. Jón Eythórsson discovered these little guys in Iceland and named them “jökla mýs,” which does indeed translate to glacier mice. Did he name them that because of their size? Possibly. It could also be because they move–and not just from the wind. (1, 2, 3)
The Herd On The Move
Scott Hotaling, Timothy C. Bartholomaus, and Sophie L. Gilbert submitted a paper entitled “Rolling stones gather moss: movement and longevity of moss balls,” on June 29th, 2019. Exactly ten months later–April 29th, 2020, Polar Biology published their paper. The trio studied some of these glacier mice which had formed on the Root Glacier in Alaska. They seemed to move, all together, about an inch (2.5cm) a day, South, then Southwest. They don’t appear to be moving by being pushed around by the wind (as opposed to when they’re developing, where wind movement helps them to form) or sliding down the glacier’s slope. They’re also not moving to seek out the sun, but instead “their movements are positively correlated with glacier ablation.” (4)
What Is Glacier Ablation?
Ablation seems like it must be some exciting and mysterious force, compelling these moss clumps to move, ever-onward, towards it. However, ‘ablation’ is just melting. In glaciers that end on land, the sun will melt the surface area of the glacier, which causes the majority of the ablation. This run-off forms little rivers, carrying the meltaway. If it ends in a body of water, the ablation will take the form of pieces of the glacier splitting off (called “calving”) into icebergs. Lower parts of the glacier are referred to as the “ablation zone,” because they typically are losing more mass than they gain over the course of a year. (5)
Why Is This Happening?
Stumped? You’re not the only one. The “Rolling stones gather moss” paper says that though glacier mice are “widely reported [on], no studies of their movement and persistence across years have been conducted.” They go on to say that the resulting “knowledge gap” should be addressed, especially “considering the degree to which glacier moss balls may represent viable, long-term biotic habitats on glaciers.” In a 2012 New York Times article, it’s stated that glacier mice “often accumulated a lot of dust in their travels and could potentially function like roving sponges, soaking up water wherever they went.” Is this absorption the cause of the movement? Hotaling, Bartholomaus, and Gilbert still don’t know, saying they “could not explain the direction of moss ball movement. . .it appears a still unknown external force influences glacier moss ball movement on the Root Glacier.” (1, 4)
