Observation: Cardiac Bowl

Observation Date
10/31/2019
Observer Name
Peter Donner
Region
Salt Lake
Location Name or Route
Cardiac Bowl/Ridge
Red Flags
Red Flags
Poor Snowpack Structure
Comments
Toured Collins Gulch Sunday 10/20 and every day from Tuesday 10/22 to Wednesday 10/30. Thanks again to Alta for allowing uphill traffic.
Based on my observation of Collins Gulch the past week and a half and my expectation the avalanche hazard would be low Thursday 10/31, decided to tour the Cardiac area.
Snowpack in the Alta perimeter is comprised of two storm cycles and 4 events beginning 10/18. Snowbird snotel reports snow depth of 4 inches 10/18 and 13 inches 10/20, for the first cycle. The second cycle begins w 8 inches depth 10/27 increasing to 10 inches 10/28, 13 inches 10/20 and 18 inches 10/30.
In approximate terms, my observation of Collins Gulch is the 10/18 storm was about 6 inches, the 10/20 storm was about a foot, the 10/27 storm was 6 inches and the 10/29 storm was about a foot. Roughly 3 feet of snow from 10/18 to 10/29 on essentially bare ground.
As of 3pm 10/31 the Snowbird snotel is reporting 12 inches depth and the Collins snowstake is reporting 23 inches. (Collins had been reporting 4 inches high but 23 inches seems about right.)
Isolated 5 columns during the day Thursday 10/30 in north facing upper Cardiff with the common result of failure on the 10/18 layer, which is 15 to 30 inches down, depending on location. Chronologically, the columns were 1. under Cardiff Peak (10,200 elevation); 2. on the traverse from LSB to Cardiac Bowl (9,900); 3. at the top of my first run in under the east chute in Cardiac Bowl (10,600); 4) at the top of my second run under west chute in Cardiac Bowl (10,700) and at the top of my last run on Cardiac Ridge (10,200).
Snow depth varies from 1 foot to 3 feet in Cardiac Bowl depending on locally windward or leeward. The heat vent near east chute is actually bare ground. Skinner was in under LSB to Cardiac Ridge but Cardiac Bowl had not been skied. In his ob from Wednesday 10/30, Dave H. reports traveling this area. On Thursday, 10/31, I broke trail up the Bowl following the standard route on the subridge separating west facing LSB from Cardiac Bowl, with an ascending traverse under the Superior rock bands. No cracking or collapsing while breaking trail.
The pack varies from Cardiff Peak to Cardiac Bowl, within the Bowl, and to Cardiac Ridge. Column 4 at 10,700 under west chute sticks in my mind as it was a clean shear at the 10/18 layer, under a dense foot of 4 finger snow from the 10/20 storm, which in turn is under 18 inches of 1 finger light snow from the 10/29 cycle. Not a bad structure except that the base is weak. Perhaps because it is more east-facing and sun exposed, Cardiac Ridge had less snow than the Bowl, about 2 feet, and it is weaker and less cohesive, though still consolidated enough to fail on the 10/18 layer. Less pronounced, but still strong snow on top of a weak base.
Going forward, if we have a series of small storms in late November, the base will compact and strengthen while the overall pack stabilizes. If we have high pressure into December with no snow and then a big dump Cardiac could run full track wall-to-wall, with the 10/18 layer acting as a greased bed surface.
For the time-being until our next storm, it seems it will be difficult for a human to trigger an avalanche in any terrain except the most radical. Rocks and logs will be the main hazard.
Today's Observed Danger Rating
Low
Tomorrows Estimated Danger Rating
Low

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