Stubborn Collapses

CB Avalanche Center2020-21 Observations

Date of Observation: 01/02/2021
Name: Ben Ammon

Zone: Southeast Mountains
Location: Snodgrass
Aspect: North, North East, East
Elevation: BTL

Weather: Winds calm to light BTL
Skies clear to scattered
Snowpack: Still observed multiple collapses but some much more stubborn than in past days. One collapse occurred while the group was taking a break, and people were standing and moving around, and then someone found the right spot and the whole meadow dropped.
We dug at 10,900 feet on a NE aspect that was very sheltered and near the dark timber.
HS 80cm 35cm F hard FC, 20cm 1F- mixed forms (12/10 storm), 25cm F-4F DF/FC (12/28 storm)
CT19 down 25cm (12/10 interface) and CT25 SC down 45cm (Nov FC)
ECTN29 down 45cm
ECTN24 down 45cm

 

Quieting snowpack

CB Avalanche Center2020-21 Observations

Date of Observation: 01/02/2021
Name: Zach Guy

 

Zone: Northwest Mountains
Location: Poverty Gulch
Aspect: North, North East, East
Elevation: 9,600 – 12,200

 

Avalanches: One small natural wind slab that ran last night or this morning (E, NTL). No other fresh avalanches observed.
Weather: Moderate winds with light transport. Clouds increased through the day with a few snow flurries this afternoon.
Snowpack: Skinned, snowmobiled, stomped, and skied on dozens of previously untrammeled low angled slopes (mostly near/below treeline) without any obvious signs of instability today, in stark contrast to just about every tour in the past few weeks. It appears as if the snowpack in this deeper part of the zone is moving to a low likelihood, high consequence persistent slab problem. On a NE aspect near treeline, the slab is about 4 feet thick, mostly 1 finger hard. The 12/10 interface is 4F- to F+ 1.5 mm facets. Stability tests produced a mix of hard, propagating results (ECTP30) and propagation during isolation (ECTPV, which might have been user error).

 

Photos:

[/gravityforms]

Small persistent slab

CB Avalanche Center2020-21 Observations

Date of Observation: 01/02/2021
Name: Pamela Taylor

 

Zone: Southeast Mountains
Location: Walrod Gulch trail
Aspect: South East
Elevation: 10,185

 

Avalanches: See photo.  It looked like it was triggered by an animal, as a line of tracks led to the break.  Skin tracks headed north on the trail were buried by debris but were present on the other side.

Photos:

Cement Mountain West Ridge Avalanche ob

CB Avalanche Center2020-21 Observations

Date of Observation: 01/02/2021
Name: Andrew Breibart

 

Zone: Southeast Mountains
Location: West ridge-Cement Mountain
Aspect: North East
Elevation: BTL

Avalanches: Observed a recent storm slab avalanche with unknown trigger but likely natural due to wind loading from strong SW winds during the night of 12/28-12/29 and additional snowfall with 1 inch of SWE (12/29/20 archive CBAC Weather) on a shallow snowpack in the SE zone. That’s a guess. Figure its in the R2-D2 category but cannot be certain from today’s vantage point across the Cement Creek Valley.
Weather: light winds and overcast.
Snowpack: Just skiing the road due to non supportive snow in the area. Surface hoar is widespread and has a length of at least 2mm.

 

Photos:

Upper Cement

CBAC2020-21 Observations

Date of Observation: 01/01/2021
Name: Eric Murrow, Zach Kinler, Zach Guy

 

Zone: Southeast Mountains
Location: Upper Cement Creek
Aspect: North East, East, West
Elevation: Near and below treeline to 11,800′

 

Avalanches: This area got about 6″ of snow from Monday night’s storm and we saw limited evidence of natural activity from storm. A few D1 to 1.5s on easterly aspects. No avalanches triggered today.
Weather: Increasing clouds, a snowflake or two, light winds.
Snowpack: In Lower Cement, the persistent slab structure is poorly developed without enough snow to make a slab. As we gained elevation further up the basin (around 10,000′ near Block and Tackle trail), we started noticing shooting cracks and collapses. The slab is soft and a foot thick over fist hard depth hoar (3-4mm).  The snow surface and slab are faceting.  In less sheltered areas, there is a pencil hard wind crust near the 12/10 layer helping making for a drastic hardness change near the bottom of the slab. We experienced shooting cracks on both westerly and easterly aspects. In more wind affected areas, the collapses were localized to just drifted areas. We traveled adjacent to a few steep slopes and got them to collapse and crack remotely, but not avalanche.  We also got repeatable ECTPV results on the 12/10 layer in a pit on a NE aspect NTL.

 

Photos:

[/gravityforms]

Slate River

CBAC2020-21 Observations

Date of Observation: 01/01/2021
Name: Evan Ross

Zone: Northwest Mountains
Location: Slate River
Aspect: North East
Elevation: 9,000-11,400ft

Weather: The clouds came and then went again. Calm winds. Nothing notable.

Snowpack: The snowpack in this area is really variable given all the past avalanche activity it has seen throughout December. So it’s hard to make a call on the general stability. We traveled more aggressively on steep slopes where we had high confidence there wasn’t a current persistent slab avalanche problem due to past activity. We kept it real conservative where the conditions were unknown or undisturbed. The 12/10 interface remained the primary layer of concern. The more recent 12/22 layer of facets was observable, but we didn’t encounter any particular concerns there.

We didn’t get much for direct feedback, or obvious signs to instability. A few collapses and some shooting cracks all took some effort to produce. Confidence in the snowpack structure, where undisturbed, still remains low.

The upper 10 to 15cm’s of the snowpack is losing strength. SH was also widespread all the way to ridgeline. The slab had broken down the most at lower elevations below about 10,000ft.

Strong slab on SE facing terrain

CB Avalanche Center2020-21 Observations

Date of Observation: 12/31/2020
Name: Aaron Peterson

 

Zone: Northwest Mountains
Location: Washington Gulch
Aspect: South East
Elevation: 11,500

 

Avalanches: We did not observe any new slides.
Weather: Clear, calm, and gorgeous.
Snowpack: We traveled on south through east facing terrain to the east of Elkton and felt routine collapsing on and off the skin track. Most notably, our pit showed a relatively firm (1 finger plus, almost pencil hard) slab resting on 40cm of basal facets. Test results on this interface were hard to trigger (CT 22- resistant, and ECTX), however they propagated easily (PST 34/100 end). The slab was stubborn and sturdy, but still scary. As if to drive the point home, after demolishing our pit I stepped aside and onto a thinner patch of snow near a wind blown feature. This triggered a very large wumph across our snowfield. “Nearly pant altering” according to my partner. We were incredibly happy not to be on steeper terrain.

 

Photos:

Brush Creek TH area – collapse city and remotely-trigger avalanche

CBAC2020-21 Observations

Date of Observation: 12/31/2020
Name: Eric Murrow

 

Zone: Southeast Mountains
Location: Low elevation east-facing terrain at bottom of Mount Crested Butte above East River
Aspect: North, North East, East
Elevation: 9,000 – 9,800′

 

Avalanches: Remotely trigged 3 very small D1’s on east-northeast aspect from a single collapse that propagated around 300-400 feet
Remotely trigger a D2 avalanche from about ~500 feet away that traveled through several terrain features and mature aspen groves
Weather:
Snowpack: Slopes very near valley bottom felt incredibly weak and produced regular collapsing but only traveled 20 or so feet. As I ascended just a few hundred feet above valley bottom on east and northeast terrain, the collapsing started to propagate hundreds of feet to slope scale size. Slab formation since 12/10 is only about 40cm thick and mostly fist hard with a small amount of 4finger. It rests on well-developed facets around 3mm in size. Total depth on east and northeast slopes averaged around 65cm. The snowpack was screaming to avoid all avalanche terrain and so that’s what I did, but managed to be surprised by collapses rolling through low-angled, mature aspen forest and triggering adjacent slopes. The snowpack in this area is incredibly reactive and steep slopes feel like a sure bet for an avalanche.  Small surface hoar observed on northerly slopes.

 

Photos:

 

Large remote triggered persistent slab

CBAC2020-21 Observations

Date of Observation: 12/31/2020
Name: Zach Guy

 

Zone: Northwest Mountains
Location: Mount Emmons
Aspect: North, North East, North West
Elevation: 9000’ to 12,200’

Avalanches: Remotely triggered a large (D2) persistent slab from about 350 feet away. The slab was about 3 feet thick and 300 feet wide, on a north aspect above treeline.
Handful of previously unreported natural persistent slabs to add to the list from the last cycle. D2 up Peeler basin (E, ATL) and several D2s in Wolverine and Redwell Basin (NW, NTL).
Weather: Partly cloudy midday with clear skies on either end. Light winds
Snowpack: Large, rumbling collapses on low angle terrain still the norm on almost every open slope or small clearing in trees. Collapses are getting a little more stubborn now; sometimes it was the first person breaking trail, sometimes the 2nd or 3rd in line, and sometimes it requires a hard stomp.
Snow surface is faceting. Below treeline slopes that have previously avalanched in mid-December had good stability today.

 

Photos: