| Pete Wilda,
a Fairbanks reader of this column, wants to know how the snow here
can bend off railings and loop from power lines without breaking.
He grew up in eastern Wisconsin and doesn’t remember the snow
defying gravity there.
Snow tilts and bends in Interior
Alaska because there’s not much wind and because it’s
cold, said Matthew Sturm of the Cold Regions Research and Engineering
Laboratory in Fairbanks. Sturm is one of a handful of Alaska scientists
who study snow. He enjoys it so much that a few years ago he made
a snowmachine traverse from Nome to Barrow, digging snowpits and
taking samples along the way.
“At low temperatures, the snow deforms slower,”
Sturm said of the bending snow phenomenon. “In warmer places
like Colorado, a dollop of snow that begins to lean may topple in
a shorter time than the snow here.”
A few other variables are responsible for our leaning
towers of snow, Sturm said. The snow in Interior Alaska contains
a lot of air, so gravity doesn’t pull on it as strongly as
it does wetter, heavier snow. Also, cold weather tends to prevent
snow from thawing and lubricating the contact point between the
snow and the wire or fencepost.
Having solved the mystery of the slanting snow,
Sturm explained a unique quality of snow that causes trails to set
up after the passage of feet, tires and snowmachines. Snow “sinters,”
which means that it bonds together without having to melt.
“You just stick the ends together, and snow
becomes a cohesive unit,” Sturm said. “Without sintering,
snow would behave like loose sand. I took a picture of snow on my
windshield the other day that slid down in rolls, just like a carpet.
Sand could never do that.”
Snow crystals begin bonding to other crystals after
they drop from the sky and continue the process on the ground. Sintering
happens faster when fragile snow crystals are shattered, as when
snow falls off a roof or when a snowmachine packs down powder snow.
With more sharp points touching one another and less air in the
snowpack, the snow can turn from sugar to concrete. The more disturbed
the snow grains, the harder they will set up, Sturm said. Wind is
a great producer of snow slabs as it smashes snow grains into one
another. One of Sturm’s favorite experiments is to take a
Shop Vac outside, suck up some snow, and leave it for a few hours.
“When you take it out of there, it’s
hard as a rock,” he said.
Though many people talk about trails setting up
better in colder weather (and colder snow is indeed harder than
warmer snow), the sintering process goes faster when it’s
warmer, Sturm said.
“You want active molecules,” he said.
“The closer they are to the melting point the more vigorous
(sintering) is.”
As the snowpack sinters, it seems to deflate even
when the temperature stays below freezing. That’s one of the
reasons why the National Weather Service might say 60 inches of
snow have fallen this winter, but you only see about two feet on
your roof.
“New snow settles pretty rapidly,”
Sturm said. “Over time, the whole snowpack will settle. It
doesn’t shrink; it’s more like pushing air out of a
sponge.”
Sturm said people in Fairbanks and other subarctic
continental locations can be proud of the “near-perfect”
snow that falls here. The snow of Interior Alaska is some of the
lightest snow that falls. Because there’s little wind, snow
crystals often reach the ground without colliding with other crystals,
preserving their six-pointed perfection for a few moments before
merging with the snowpack, or adding to that rope of snow hanging
from the power line. |
