Shifting snows on Niwot Ridge

I just set up my first time-lapse camera on Niwot Ridge, Colorado, with CU-undergraduate Gage Hamel.

What do we hope to capture? Fallen snow shifts like sand, and sets like cement. It forms regular features, which range from dart-like crescents to ripples, waves, and elongate sastrugi. These snow features affect the reflectivity and aerodynamic roughness of the snow, which in turn determine its temperature and melt rate.

My aim is to measure and quantitatively predict the way these features form and change in time. The first stop is to get detailed observations of a changing snow surface. The field site is Niwot Ridge, where the University of Colorado keeps a weather station and the wind carves deep sastrugi.

Below are two time-lapse videos of snow on the ridge (photos: Sarah Evans). These are examples of the textures and changes we hope to quantify.

This gif shows waves of powdered snow chasing downwind across the landscape:

Snow_waves_move_across_Niwot_Ridge_Colorado

In this four-day timelapse the snow edges are worn back by the wind (coming from the left). Then they set, and remain almost motionless until a new storm erases them at the start of February.

Shifting_snow_on_Niwot_Ridge_Colorado

 

 

These videos show us that snow features move. I’m looking for how. My camera will take photos every few seconds. That should be enough to see perturbations grow and move over the waves.

Snow features on frozen lakes

This winter, I’ve started to study snow bedforms. When snow falls, it settles into soft blankets – unless it gets caught by a strong wind. In Colorado, some of our strongest winter winds appear in the Front Range, where cold air falls over the Continental Divide towards the plains. When the wind picks up snow, it forms fantastic, ordered bedforms, like pointed sastrugi:

Sastrugi point towards the wind

and dune-like crescents:, both big:

Snow crescent angled into the wind

and little:

A small snow crescent on a frozen lake

I took these photos with CU-Boulder undergraduate Clea Bertholet for scale.

In the coming weeks, I plan to start taking measurements and (eventually) build a model of snow bedform development in different wind and snow conditions. For now, we’re scouting snow conditions around Colorado.