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Potential (historic) avalanche in Juneau,AK building up

4,035 Views | 20 Replies | Last: 28 days ago by jetescamilla
jetescamilla
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Didn't really know where else to post this but figured the outdoor board would be most interested. We've had a weird snow season and had a dump of snow earlier in the year with a drastic cold spell creating a very thick hard layer that the later season snow is building on. Think of these like cake layers and the differing snow types, temperature, humidity, wind all factor into the friction between layers. Then factor that the wind drives snow into overhangs over mountain ledges creating unstable surfaces.

In town here there are multiple avalanche paths that scar the mountains, most are not threatening unless you're in the backcountry. However there's some sections near downtown that were built in an avalanche path and the avalanche hazard has reached "historic" levels. The largest of which is the Behrends Avenue Path shown below. The city puts out daily avalanche hazards and 2 days ago during a wind/snow event it was listed as a level 5 extreme for the first time. Local police and firemen went door to door precautionarily evacuating all homes shown in the map below. Fortunately nothing came down because estimates have determined it will be a historic event and go over houses and block the highway with 14ft of snow. Unfortunately that also means that the threat is still there and it can still keep building while other snow/wind/rain events have the potential no knock it down.

The city of Juneau put's out an avalanche advisory every morning and is based on the weather conditions for the day. Important to note that the advisory is for the area as a whole, not just one path. Additionally, just because a threat is lowered to a 3 doesn't indicate a hazard is safe, these things can go at any time.

Last week we housed a coworker and his wife who live in the "B zone" shown below when the threat was a level 5. Unfortunately our space was only available for 3 days as we had someone book our attached vacation rental prior to this and my coworker and his wife are now staying with other friends until things get settled. They're reluctant to go home even as predictions lower because there's always the potential that this let's loose and it engulfs their house. At this point they're almost wishing it would just go and let the chips fall where the may (assuming everyone in the area has evacuated).

Hopefully this google link works getting you to the location of the avalanche. It's easy to identify because of the scaring on the mountain bare of trees. You can see the path down to the upper level of the neighborhoods.
https://goo.gl/maps/LxCMwiHkc8WWV7wo9

This street view map is looking up at the mountain from the highway/harbor that has the potential to be engulfed. Even though all the summer vegetation is green you can easily distinguish the avalanche scar by the large area with no tree growth.
https://goo.gl/maps/4zvxU14Hy1wz2mpJ9

If you're all curious feel free to follow click the links daily to see what the forecast is. I'll be sure to update if the avalanche ever happens.

https://juneau.org/emergency/current-advisory

2011 Avalanche Study - http://media.ktoo.org/2016/07/SLF_2011_Study.pdf





Random news articles of the potential for the avalanche and evacuations of homes:
https://www.ktoo.org/2021/02/27/juneau-sets-up-evacuation-center-for-residents-affected-by-extreme-avalanche-danger/
https://www.ktoo.org/2021/02/26/juneau-officials-warn-of-dangerous-historic-avalanches-and-potential-evacuations-of-neighborhoods-if-conditions-worsen/
https://www.usatoday.com/story/news/nation/2021/02/28/avalanches-juneau-alaska-deadliest-month-us-history/6862272002/


This is a recording of a Behrends Ave avalanche in 2017. This does happen quite often but the avalanches usually let loose before they build up too big and dissipate before getting to the house. The land flattens behind the houses...somewhat. As the linked pdf report above says the 30 year and 300 year avalanche will reach the houses and/or the highway.

clem93
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Fascinating stuff. Thanks for posting.

Stay safe!
45-70Ag
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Terrifying and the power of those things is unreal.
nortex97
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Imagine trying to sell a house there right now, and the inspector nixes it because "might be destroyed by an avalanche next week."

Ugh.
Stasco
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Serious question. Is that avalanche expected to completely flatten most of the houses? Or would they stay mostly intact? I'm sure there would be severe structural damage, but I'm wondering what your chances of survival would be if you were in a house when the avalanche hit. If you had good clothes, water, food, and a shovel, could you dig yourself out?
Old RV Ag
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Sounds like they need a couple 75mm howitzers to trigger the avalanches before they get too big. Lots of places (especially ski resorts) do it. This isn't anything new so wonder why they don't.
ccard257
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Old RV Ag said:

Sounds like they need a couple 75mm howitzers to trigger the avalanches before they get too big. Lots of places (especially ski resorts) do it. This isn't anything new so wonder why they don't.
yeah this was my initial thought. Not just ski areas...CDOT in colorado blasts paths all the time that threaten highways if they build up.
jetescamilla
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Old RV Ag said:

Sounds like they need a couple 75mm howitzers to trigger the avalanches before they get too big. Lots of places (especially ski resorts) do it. This isn't anything new so wonder why they don't.
This is often done in other avalanche zones in the area. In fact, there's one happening today.
https://www.juneauempire.com/news/dotpf-conducts-avalanche-risk-reduction-along-thane-road/


There are 2 reasons why this path doesn't get preventative avalanche triggers.
  • 1. A trigger has the potential to escalate into a larger than anticipated avalanche and impact houses.
  • 2. The mountain has numerous avalanche paths and a trigger of the Behrends has potential to cause a secondary avalanche on the Bathe Creek Path. This area has trails frequented by hikers/cross country skiers and could injure or kill people in it's path. There are too many variables to control to ensure no one will be present during these operations.
Not that I expect anyone to read all of the dump I did on the OP but this is addressed in the PDF avalanche report linked above.

Quote:

The main risk of artificial release above settlements is triggering an avalanche that is too large to manage and results in damages. In order to apply artificial release by explosives the avalanche situation must be studied in detail. Important points are evaluating the terrain features in regard to the effectiveness of artificial avalanche release, the potential for triggering secondary avalanches and the existing damage potential.

Conclusions We do not recommend applying the artificial release of avalanches in the Behrends Avenue avalanche path under the current conditions. The risk to persons and buildings is much too high.


ATL Aggie
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Old RV Ag said:

Sounds like they need a couple 75mm howitzers to trigger the avalanches before they get too big. Lots of places (especially ski resorts) do it. This isn't anything new so wonder why they don't.


Exactly, it seems odd that they don't
Bandit99
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And I'm late to the party.
jetescamilla
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Not certain if this video link works but this is today's avalanche control and is much bigger than typical crossing halfway across the channel. Note this slide gets control regularly and the above in discussion had yet to be released once this year.

https://www.facebook.com/313380332197871/posts/1647872018748689/
Dumb_Loggy
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I'll be following this thread for your updates. Good luck!
jetescamilla
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We've had quite a few spring like days in a row and our snowpack has firmed up bringing the avalanche hazard down to a 2 rating. However, we have a forecast of up to 8 inches of heavy snow starting tomorrow afternoon and going through the next day. It's anticipated that he avalanche hazard shoots back up to a 4 or higher, but we won't know until 7AM. If it sneaks into a 5 again they'll most likely ask houses to evacuate again.

Quote:

...WINTER STORM WATCH REMAINS IN EFFECT FROM WEDNESDAY AFTERNOON
THROUGH THURSDAY MORNING...

* WHAT...Heavy snow possible. Total snow accumulations of 4 to 8
inches possible.

* WHERE...Juneau.

* WHEN...From Wednesday afternoon through Thursday morning.
TommyGun
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Old RV Ag said:

Sounds like they need a couple 75mm howitzers to trigger the avalanches before they get too big. Lots of places (especially ski resorts) do it. This isn't anything new so wonder why they don't.


Nothing like pulling into Little Cottonwood Canyon in Snowbird, UT and hearing the howitzers echo on the morning after a big dump of snow. You always knew it was going to be a great day and the cannon shots definitely got your blood pumping.
rebag00
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How much snowfall is "normal" for Juneau in a year?
Aggie_3
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Wow
Aggie_3
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jetescamilla said:

We've had quite a few spring like days in a row and our snowpack has firmed up bringing the avalanche hazard down to a 2 rating. However, we have a forecast of up to 8 inches of heavy snow starting tomorrow afternoon and going through the next day. It's anticipated that he avalanche hazard shoots back up to a 4 or higher, but we won't know until 7AM. If it sneaks into a 5 again they'll most likely ask houses to evacuate again.

Quote:

...WINTER STORM WATCH REMAINS IN EFFECT FROM WEDNESDAY AFTERNOON
THROUGH THURSDAY MORNING...

* WHAT...Heavy snow possible. Total snow accumulations of 4 to 8
inches possible.

* WHERE...Juneau.

* WHEN...From Wednesday afternoon through Thursday morning.



Any update
jetescamilla
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The "storm slab" as the city emergency management calls it is still hanging on. Since it never released we've had a run of cool sunny days which helps to settle the snow down. However, the threat always remains and a small avalanche can still trigger the whole thing. Conveniently today we're in a winter weather advisory for 5 to 12 inches of snow with blowing wind.

Quote:

...WINTER STORM WARNING REMAINS IN EFFECT UNTIL 10 PM AKDT THIS
EVENING...

* WHAT...Heavy snow expected. Total snow accumulations of 5 to
12 inches. Winds gusting as high as 30 mph.

* WHERE...Juneau Borough and Northern Admiralty Island.

* WHEN...Until 10 PM AKDT Monday.


Below is a photo showing the cornice built up on a different mountain in town. This one doesn't have residential areas in it's path. It's also aptly named "Thunder Mountain" because of the high number of avalanches that get released naturally on it every year. But it's an excellent example of how the wind driven snow will keep building until it finally let's loose.

Old RV Ag
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jetescamilla said:

The "storm slab" as the city emergency management calls it is still hanging on. Since it never released we've had a run of cool sunny days which helps to settle the snow down. However, the threat always remains and a small avalanche can still trigger the whole thing. Conveniently today we're in a winter weather advisory for 5 to 12 inches of snow with blowing wind.

Quote:

...WINTER STORM WARNING REMAINS IN EFFECT UNTIL 10 PM AKDT THIS
EVENING...

* WHAT...Heavy snow expected. Total snow accumulations of 5 to
12 inches. Winds gusting as high as 30 mph.

* WHERE...Juneau Borough and Northern Admiralty Island.

* WHEN...Until 10 PM AKDT Monday.


Below is a photo showing the cornice built up on a different mountain in town. This one doesn't have residential areas in it's path. It's also aptly named "Thunder Mountain" because of the high number of avalanches that get released naturally on it every year. But it's an excellent example of how the wind driven snow will keep building until it finally let's loose.


That one's so ready, a hand grenade from a chopper would trigger it. Hell, the chopper turbulence might trigger it.
PrestigeWorldwideAg12
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A fart might trigger that thing.
jetescamilla
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Quick update as we've gotten quite a bit of new heavy wet snow. We also have winds gusting on the mountains up to 70 mph pushing on the unstable snow. Last night there 2 natural releases that "crossed the road" at the Thane avalanche path. Local DOT webcams caught the slide. We're sitting a level 4 for the time being. Any release of the Behrends path has potential to be catastrophic still for those homes immediately below.

Facebook video from Alaska DOT showing the webcam footage of the slide late last night.
https://fb.watch/4ifYqrvgP0/
https://www.facebook.com/307611695931225/videos/908431369917717

https://juneau.org/emergency/current-advisory
Quote:

With another 6.5" of snow over the last 24 hours bringing our 2 day total in the region up to 21.5" of new snow avalanche danger remains HIGH today. Natural avalanches have been occurring and remain likely today human triggered avalanches are more than likely.
We have seen a great number of storm slab and wind slab avalanches naturally release in the region over the last 36 hours. The White subdivision partially released, other prominent non urban paths on the North aspect of Mt Juneau slid. Thane road had powder blasts reach the road at both Snowslide Creek and Cross Bay. The Cross bay avalanche appeared to be several hundred yards wide and had a crown that appeared to be 6' or better deep. I would assume this is on our Deep Persistent Slab that we have been concerned with in the region. Even the Dan Moeller trail had 2 of its prominent wind loaded avalanche paths slide heading up to the bowl.
Eaglecrest Temps Low-25f, High-26f, Current-26f. Mt Roberts Low-27f, High-31f, Current-30f.
Eaglecrest current winds ESE 19-25mph. Peak gusts to 39mph. Mt Roberts Current winds ESE 13-15mph. Peak gusts to 27mph from the ENE. Of interesting note winds traded between ESE and ENE. These ENE winds we had from 2pm to midnight last night will have increased load and sensitivity in the urban avalanche paths today. Winds increasing this afternoon will increase the likelihood of natural avalanches.
Eaglecrest received 20cm new snow from 16mm SWE. The tram picked up 16cm new snow from 13mm SWE. Of more interesting note are our two day totals. We picked up 55cm (21.5") of new snow over the last 48 hours.
The National Weather Service Forecasts-

...WINTER WEATHER ADVISORY IN EFFECT UNTIL 10 AM AKDT THIS MORNING...
* WHAT...Snow. Around 4 inches of snow fell overnight with an additional accumulation of 1 to 2 inches through the morning.
* ADDITIONAL DETAILS...Wet, slushy snow will be difficult to manage. A change to rain expected through the morning with snow
levels rising to around 700 feet.
Today- Snow early in the morning, then widespread rain showers, heavy at times in the afternoon. Snow accumulation 1 to 2 inches. Snow level rising to 700 feet in the afternoon. Highs around 39. east wind 10 mph becoming southeast 20 mph in the afternoon.

Tonight- Widespread rain showers in the evening, then numerous snow showers. Snow accumulation to 2 inches. Lows around 30. Southeast winds 10 to 20 mph.

Thursday- Decreasing clouds. Scattered snow and rain showers. highs around 38. East wind 10 mph in the morning becoming light and variable.

The forecast is calling for around another 3/4" SWE in the next 24 hours. More than enough to keep us concerned with natural avalanches of both wind slab and storm slab.

Of concern is the warming today. Although they have dropped the temp model and freezing level over the last 24 hours by several degrees. This should help a great deal in maintaining stability. Yet with temps still rising a few degrees be concerned of a weakening snowpack. Also be aware that wet loose avalanches are possible at lower elevations today.

Winds remain a concern especially as noted with 12+ hours of NNE winds in the urban zones may have increased sensitivity. Be aware that we will have weak windslabs on multiple aspects in the region from the shifting winds yesterday. Increasing winds this afternoon will again raise concern.

Please continue to limit your time spent in avalanche terrain. Please continue to avoid the Flume Trail and avoid the areas above the gates in the Behrends Neighborhood. These paths have not seen activity lately and have potential for not only large storm slabs but also for historic deep persistent slabs should these deeper weak layers come into play.


https://www.ktoo.org/2021/03/17/high-avalanche-danger-closes-thane-road/
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