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.

 

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Bluebird views

CBAC2020-21 Observations

Date of Observation: 12/30/2020
Name: Zach Guy

 

Zone: Southeast Mountains
Location: Coney’s
Aspect: North East
Elevation: N/BTL

Avalanches: Good views of the leeward aspects of the Northwest Mountains. Plenty of evidence of storm slab instabilities that ran throughout the storm, D1 to D2. A few slides looked like they broke into deeper layers, up to D2.5. Attached photos highlight the largest or most interesting activity.
We triggered a small storm slab (1 foot thick) on a rollover.
Weather: Clear, cold, calm winds.
Snowpack: Stepping off the beaten track we got frequent rumbling collapses and shooting cracks on basal weak layers. On shady aspects, we also got cracking at the storm snow interface about a foot down.

 

Photos:

Email ob from Red Lady skin-track

CBAC2020-21 Observations

Date of Observation: 12/30/2020

 

Zone: Southeast Mountains
Location:
Aspect: South East
Elevation:

 

Avalanches: The photo below was taken at approximately 11 am on Wednesday, 12/30. From the skin track on Red Lady above tree line, a party of three of us saw two skiers come down the bowl, stop for a while in the circled spot, and remotely triggered the slide spotted lookers left to them maybe a minute or two after they had stopped there. We weren’t sure if they had stopped there for a particular reason and/or if they had noticed the remote slide. (Submitted by CBAC Forecaster from an email)
Weather:
Snowpack:

 

Photos:

 

Evans Basin

CBAC2020-21 Observations

Date of Observation: 12/30/2020
Name: Eric Murrow

 

Zone: Northwest Mountains
Location: Evans Basin steep easterly shots
Aspect: East, South East, South
Elevation: 9,500′ – 11,200′

 

Avalanches: A couple of avalances in steep southeast terrain in Red Lady glades – near treeline type features. Look like storm slabs running on the old crust. Likely failed very early AM of 29th.
One D2 at the very end of Moonscape Ridge by Evans basin – ENE-facing very drifted BTL feature
Weather: Ugly cold at valley bottom in the morning, but comfortable temps near and below treeline in the sun. No snow transport observed on nearby high terrain.
Snowpack: Solar radiation moistened the snow surface on SE, S, and SW slopes up to 11,200′. Made for interesting breaker-crust skiing at 3pm once it started to refreeze. Relentless collapsing on low-angled terrain on the ascent. Lots of collapses on flat ridgeline above steep east-facing slopes but very little cracking and no resulting avalanches, hmmmm. Skied down a short steep east-facing slope without result, but probing sure confirmed the suspect structure below. Dug a couple of test profiles checking on SE facing features to see if the crusts below the new slab is a potential Persistent Slab problem; slab seems not quite cohesive and heavy enough to cause an issue at locations traveled up to 11,200′, BUT a disconcerting double-crust setup exists below the slab. Recent storm snow was around 30 – 35cm thick but still Fist to Fist+ hard and bonding poorly to the crust below (see photo). On collapse ran 100+ feet and shot cracks across a tiny NE-facing slope down to the 12/10 interface; upon inspection Surface Hoar (~5 – 8mm) was found below the recent storm at the likely 12/22 interface. Easily ID this interface with shovel tilt’s tests.

Photos:

 

Morning avalanche obs

CBAC2020-21 Observations

Date of Observation: 12/30/2020
Name: Zach Guy

 

Zone: Northwest Mountains
Location: Scarp, Peeler, and Gothic
Aspect: North East, East
Elevation: ATL

 

Avalanches: See photos. Several slab avalanches D2, maybe up to D2.5 on E and NE aspects ATL that likely ran early yesterday.

 

Photos:

Avalanche obs on Whetstone from the highway

CBAC2020-21 Observations

Date of Observation: 12/29/2020
Name: Eric Murrow

 

Zone: Southeast Mountains
Location: Whetstone Mountain
Aspect: North East, East
Elevation: near and above treeline

 

Avalanches: Observed natural avalanche on Whetstone at 945am.
Several avalanches on far southern end near CB south on east and northeast aspects near treeline, D1-D2
D2 avalanche in Barcelona Bowl NE aspect above treeline
D2 in Lucky Boy Bowl NE aspect near treeline

Several of these avalanches appeared to be shallow storm slabs that “stepped down” into deeper persistent weak layers

Photos:

 

Gothic 7 a.m.

CBAC2020-21 Observations

Date of Observation: 12/29/2020
Name: billy barr

 

Zone: Southeast Mountains
Location: Gothic

Avalanches: No visibility to see if any slide activity.
Weather: There was 10½” new snow with water total of 0.75″ as the snowpack sits at 32½”. Wind is calm now and the snowfall has stopped. Mild with yesterday’s high 24ºF and the current is the morning low of 11º.

 

Storm obs from Slate

CBAC2020-21 Observations

Date of Observation: 12/29/2020
Name: Zach Guy

 

Zone: Northwest Mountains
Location: Slate River drainage
Aspect: North East, East
Elevation: 9,000 to 11,200 ft

Avalanches: Decent storm slab cycle last night from Happy to Climax to Schuylkill Ridge along with a few persistent slab avalanches
Happy Chutes: Lots of small slabs and sluffs, mostly D1. A D2 persistent slab
Climax: Debris through several of the chokes, looked like more shallow storm snow instabilities but light was flat, probably D1.5 to D2.
Schuylkill: Numerous storm slabs about a foot deep that ran near to the bench, D1.5 to D2. Two small persistent slabs on lower rollers that either ran last night or today. We remotely triggered two small persistent slabs on small terrain features, about 3 feet thick.
Wash Gulch: Plow triggered persistent slab, D2.
Weather: Light snowfall in the morning. Light winds. About an inch of accumulation. Overcast in the Upper Slate, broken skies near town.
Snowpack: Numerous large collapses in open slopes on low angled terrain and in small clearings in steeper trees. Storm snow is about 12″ to 15″ below treeline and 18″ near treeline, fist hard. Persistent slab structure is about 3 feet thick below treeline (Fist down to 4Finger). Cracking at or near the storm interface, especially as we gained elevation. We tested for “repeat persistent slab structure” in terrain that slid earlier this month. The structure was not reactive in pits, but there is still a lingering persistent weak layer near the ground, just denser and smaller with less of a slab than a pristine snowpack that hasn’t slid.

 

Photos:

A lot of bark and some bite too

CBAC2020-21 Observations

Date of Observation: 12/28/2020
Name: Zach Guy, Zach Kinler, Jack Caprio

 

Zone: Southeast Mountains
Location: Gothic Road
Aspect: East
Elevation: Below treeline

 

Avalanches: Intentionally triggered a couple of small persistent slabs, about 15″ thick and up to 50 feet wide on small terrain features, failing on fist hard facets near the ground.
Weather: Light snowfall mid-afternoon started picking up in intensity to S2 around 3:30 p.m as we were leaving. Calm winds.
Snowpack: About 3″ of new snow so far. Frequent rumbling collapses and shooting cracks traveling about 30 to 50 feet. Slabs were somewhat discontinuous across terrain due to previous wind loading and scouring effects. It was easy to trigger collapses in the transition from stiffer, supportive snow to unsupportive, softer snow or vice versa. Of the few test slopes we poked at, a couple slid, while most just cracked and slumped.
The 12/22 interface is down about 5″ (mix of near surface facets and surface hoar). It was producing cracking underfoot but not shooting past skis.

 

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