Boulder’s Frosty Crystal Menace

Now that fall has faded I’ve been trying to focus on the subtlety of light play on snow. I was hiking at Chautauqua after a recent snowstorm enjoying nature’s snow drift sculptures when I noticed a gem-like sparkle glinting off of the surface of the snow banks…

Gem Covered Snow Sculpture

The snow banks were covered with feathery crystals

Crystal Covered Snow Banks

Snow Gems

When I got really close I discovered a micro-environment of delicate crystalline beauty…

Feather Like Crystals

These beautiful crystals are a type of frost called surface hoar. Here’s the physics: just as frost forms on the outside of a cold glass on a warm humid day, surface hoar forms when a snow bank cools overnight. During a cold clear night, the snow bank radiates heat causing its surface to become colder than the surrounding air. Since warm air holds more water vapor than cold air, the vapor from the warmer air above the snow will condense onto the surface. The surface of the snow bank is also colder than its interior which encourages evaporation and releases additional crystal growing moisture.  By morning the snow bank can be covered with a layer of faceted ice crystals. The best conditions for formation of hoarfrost are: cold clear nights and a very light wind to circulate humid ground air around the snow surface. These are also common conditions for Boulder in winter.

As with my earlier discovery of heart warming snow fleas, I’ve discovered that little things can have big consequences. In the case of surface hoar there is a darker side which turns these benign crystals into killers…

This Crystal Has A Dark Side

This miniscule crystal is responsible for over 150 human deaths per year because surface hoar makes a perfect avalanche trigger. When layers of surface hoar are interlaced with subsequent layers of fresh snow, thin sheets of slippery ice crystals form within the snow. This laminated snow is hard to detect and can be very unstable…

Laminated Snow Bank

These sheets tend to slip resulting in the transformation of lots of little independent snowflakes into an angry crystalline flash mob travelling at 80 mph (130 km/h). Physics has consequences…

So Many High Speed Snowflakes (photo:

3 Responses to “Boulder’s Frosty Crystal Menace”

  1. Late Winter Frost and the Promise of Spring « Tales from the Trails Says:

    […] Tales from the Trails Observations from Colorado's Hiking Trails « Boulder’s Frosty Crystal Menace […]

  2. Super Cool Cloud Trapped In Boulder Forest « Tales from the Trails Says:

    […] the way home we did catch some early snow on the Indian Peaks. It’s a harbinger of frost to come… First Snow Dusts the Indian Peaks Share this:EmailFacebookLike this:LikeBe the first […]

  3. Winter Solitude | Tales from the Trails Says:

    […] Moving closer reveals the feathery crystals of surface hoar  on the snow. This frozen frost is beautiful but deadly… […]

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