When will the snow and ice melt away? It could be a while

Minnesota doesn't have much in the way of glaciers and mountains, but this year we have the next best thing: giant snow piles.

The particularly long and snowy winter has also resulted in particularly big snow piles like the celebrated Mount Eden Prairie. The massive mound at the Eden Prairie Center became a symbol of our snow-filled winter after a red Target shopping cart was defiantly parked on its summit.

Photos of the snow pile took on such a viral life last month that the image inspired artistic renderings and t-shirts.

Mount Eden Prairie is not alone, of course. There are plenty of other snow mountains around town. According to one study of a snowy urban areas, about 15 percent of residential areas are covered with large snow piles during the winter.

Which inspires this question: How long are those snow piles going to be around?

If history is any guide, it could be nearly summer until they're completely melted away.

During the winter of 2010-2011, a big snow pile in the parking lot of what was then the Sears store in St. Paul got so big that it was dubbed the Sears Alps and became a local tourist attraction. By June, there was still an icy mound a few feet high, covered with dirt mixed with garbage.

It's no wonder that the remnants of that winter hung around so long. At the time, the winter of 2010-2011 was the fourth snowiest winter on record for the Twin Cities. But 2010-2011 just got bumped back a space because this year became the third snowiest winter on record for the area.

Variables that determine how long a pile of snow will be around include more than just warming temperatures, according to Peter Neff, a glaciologist and climate scientist at the University of Minnesota.

The size and density of the mound, the thermal mass and conductivity of the material and the amount of sunshine, humidity and rain the area experiences can affect how long it will take for the dirty snow piles to finally go away.

It isn't just a matter of exposing ice to temperatures of 32 degrees and, voila!, water.

It actually takes a bunch more energy (the latent heat of fusion, to use the technical term) for a substance to change phase or go from solid to liquid.

After a while, the snow piles may shrink to the point where they look like nothing more than a grubby pile of dirt. But there may still be an icy core hiding underneath. It's sort of a miniature version of what scientists call an ice-cored moraine: glacial ice covered with a layer of rock or sediment.

That dirt layer might actually act as an insulative coating that slows the melting of the ice beneath. Rain and humidity might hurry things a bit because water conducts heat better than air.

But if you're waiting for a real big pile of icy snow, snuggled under a blanket of grimy parking lot dirt, to disappear, "You're talking into June, and potentially later," Neff said.