Monday, May 5, 2014

Dust on the Snowscape

It's looking like this spring will yield a dusty and dirty snowpack in the Wasatch Mountains, thanks to the April 22nd dust storm from the Sevier Lake Bed (see Sevier Lake Bed Dust) and several minor events over the past few weeks, including yesterday.

Most of the dust was buried temporarily by recent storms, but given the heat of the past few days, it's now being exposed, especially in sunny areas where the new snow was thin due to wind scouring or sloughing.  Here are a few perspectives of the snirt (part snow part dirt) from Saturday.

Snirty patches at Alta Ski Area 
Snirty slough zones on Little Superior
A snirty Mount Superior
Dusty snow absorbs more sunlight than clean snow, accelerating the snowmelt.  The comparison below from the San Juan Mountains of Colorado shows that aged (i.e., not fresh), clean snow reflects about 72% of the sunlight back to space, whereas dusty snow reflects only about 43%.

Courtesy Tom Painter, JPL
At noon in mid May in the San Juan Mountains, the clean snow absorbs about 308 Watts of solar energy per square meter, whereas the dusty snow absorbs 627, 319 Watts per square meter more.  That's a huge increase.  Dust in the Wasatch isn't as dark or typically concentrates as found in the San Juan's, so the difference here might not be quite as large, but it is still going to be substantive.  The bottom line is that dust accelerates the snowmelt and reduces the duration of snow cover in the spring.  I would imagine that increased absorption of solar radiation likely results in an earlier, more rapid increase in avalanche hazard on sunny mornings as well.

1 comment:

  1. I flew from New York City to California yesterday. Our flight crossed just to the north of Grand Junction Colorado. I could see Crested Butte from the air. The snirt is striking from 30,000 ft. All the lower lying areas in the valleys looks grey.