Unofficially Colorado’s most popular “glacier,” it likely comes as a shock to some that Saint Mary’s Glacier, near Idaho Springs, isn’t actually a glacier at all according to many experts. It’s actually just a semi-permanent snowfield. This might not seem like a big deal, but there’s a big difference between these two distinct designations.

According to Google Dictionary, a glacier is “a slowly moving mass or river of ice formed by the accumulation and compaction of snow on mountains.” Capable of amassing a huge amount of weight, glaciers are responsible for carving out much of the Colorado landscape. This is where a glacier differs from a snowfield – a snowfield doesn’t really move, which means it’s not altering the landscape in a big way.

One reason why semi-permanent snowfields are sometimes mistaken for glaciers is due to the fact that they do stick around for quite some time – just like a glacier. Semi-permanent snowfields also tend to vary in size or shape overtime, something that can create the illusion of movement.

It is worth mentioning that some sources compare a snowfield to a “young glacier,” indicating that if enough snow sticks around for enough time, that snow can be compacted into ice, at which point it may move with potential to change the landscape. Other sources indicate that a “snowfield” is often created when a glacier stops moving, often due to loss of mass.

Another key piece of information that needs to be included when discussing this topic is that the definition of a glacier tends to vary from source to source, even within the same source. For instance, in one spot on its website the USGS defines a glacier by its gravity-propelled movement downhill, while in another spot, a second definition of the glacier appears that does not require movement. Most expert definitions that we could find require movement to be present when defining something as a glacier.

So there you have it – because there’s no ice in motion on Saint Mary’s Glacier, it’s actually considered a snowfield, which means it won’t be making any new mountains or valleys anytime soon.



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