Des avalanches mouillées sans cohésion sont attendues sur les pentes raides exposées au soleil pendant les périodes de réchauffement intense. Crédit : Équipe de terrain d'Avalanche Canada au Yukon MIN

La transition d’un manteau neigeux hivernal à un manteau neigeux printanier s’accompagne souvent de douleurs de croissance – et cette année ne fait pas exception. Le printemps a fait une entrée spectaculaire entre le 24 et le 27 mars, ramenant les niveaux de congélation au-dessus 3000 mètres avec de la pluie suivi d'un ciel ensoleillé. Il en a résulté un danger d'avalanche élevé et un cycle d'avalanches naturelles largement répandu. 

Dans toute la province, de très grosses avalanches ont éclaté sur des couches fragiles enfouies, s'étendant loin dans des terrains plats ou au fond des vallées – dans certains cas, ouvrant même de nouvelles trajectoires d'avalanches en détruisant des peuplements de bois matures. Beaucoup de ces avalanches ont été déclenchées par d'importantes ruptures de corniches.

De très grosses avalanches étaient courantes lors du dernier événement de réchauffement, avec des débris d'avalanches humides observés s'étendant loin dans les zones de ruissellement, comme cet exemple des Purcells. Crédit: MIN Utilisateur KOKANEER

Débris d'avalanche dans une zone de ruissellement plate et fréquemment parcourue. Crédit: MON Utilisateur DAVESLADE14

Une grosse avalanche naturelle lors du dernier échauffement qui était probablement déclenchée par une corniche. Des avalanches similaires sont possibles ce week-end, notamment avec des chutes de corniches comme déclencheur. Crédit: MIN Utilisateur DZSKIZ 

Une avalanche de plaque déclenchée par l'homme dans le nord de Monashees, qui a été déclenchée par le bas. Des avalanches déclenchées par l'homme devraient rester probables ce week-end. Crédit: MIN Utilisateur LOUISGODIN1980

En ce qui concerne le week-end et la semaine prochaine, les prévisions prévoient un retour de niveaux de congélation élevés et soit un soleil fort, soit un mélange de soleil et de nuages ​​dans la plupart des régions. Cela entraînera-t-il une répétition de l’activité avalancheuse de la semaine dernière ? C’est difficile à dire, car plusieurs facteurs clés entrent en jeu :

Même si nous n’observons pas les fortes précipitations qui ont précédé la dernière période de réchauffement, la neige récente dans certaines régions sera sensible à sa première exposition à la chaleur et au soleil.

Les couches fragiles du manteau neigeux persistent et ont continué à produire des avalanches sporadiques, même par temps plus frais. 

Cette prochaine vague de chaleur doit d'abord s'effondrer croûtes formé par le dernier cycle de réchauffement et de refroidissement avant de pouvoir affecter les couches faibles enfouies plus profondément. Les zones avec de la neige humide sous ces croûtes peuvent connaître une détérioration rapide une fois que les croûtes superficielles se décomposent.

En général, les coups de chaleur ultérieurs ont de moins en moins d’effets dramatiques à mesure que le manteau neigeux s’habitue aux variations de température.

Une croûte superficielle de soutien réduit généralement le risque de déclenchement d'avalanches. Avec le réchauffement important de ce week-end, nous nous attendons à ce que la croûte superficielle se brise dans de nombreuses régions, ce qui pourrait augmenter le risque d'avalanches. Crédit : Équipe de terrain des North Rockies MIN

Avalanche runs out into low-angle terrain. Plan your travel with large runouts in mind. Credit: MIN User ADAMRODRIGUES11

Ainsi, même si le spectacle n’est peut-être pas à la hauteur des événements dramatiques de la semaine dernière, le risque d’avalanches de très grande ampleur et destructrices demeure. C’est le moment de rester sur nos gardes et de prendre en compte une marge supplémentaire dans notre prise de décision.

Vérifiez toujours les prévisions pour votre région avant de partir – la veille au soir et le matin même, au cas où quelque chose aurait changé.

N'oubliez pas que les conditions printanières sont dynamiques et peuvent changer rapidement tout au long de la journée.

Sachez que les problèmes de manteau neigeux et d'avalanches varient considérablement en fonction de l'altitude, alors évaluez et évaluez continuellement les conditions pendant votre voyage.

Voyagez tôt dans les zones exposées au risque d'avalanche avant que le soleil et le réchauffement diurne ne brisent les croûtes et n'affaiblissent les corniches.

Planifiez soigneusement vos itinéraires de sortie en termes d'exposition au terrain avalancheux, en gardant à l'esprit le risque potentiel d'avalanche accru en fin de journée..

Évitez les sorties de trajectoires d'avalanches. Les avalanches pourraient se propager plus loin que prévu. L’exposition au plafond n’est pas toujours évidente : soyez conscient de ce qui se profile au-dessus de vous.

Sur une note positive, il s’agit d’une période de transition temporaire. Ces échauffements initiaux facilitent les changements structurels qui font passer un manteau neigeux hivernal froid à un régime diurne de fonte-gel printanier plus prévisible. Considérez cela comme un sacrifice à court terme en faveur d’une stabilité à long terme qui nous permettra de lancer ces grosses lignes en toute sécurité assez tôt !

Une rupture de corniche a déclenché cette grande dalle dans les Rocheuses du Nord, qui s'est effondrée sur une couche faible située profondément dans le manteau neigeux, près du sol.

Une importante avalanche de plaque de neige aurait été déclenchée par l'action du soleil. Crédit : Équipe de terrain d'Avalanche Canada Nord-Ouest MIN. 

Upcoming warm weather, sun, and rising freezing levels could mean another big avalanche cycle

La chaleur monte : un nouvel échauffement entraîne une augmentation du risque d’avalanche

Since posting the original article on this subject, several questions have come up. In this follow-up I’ll do my best to respond but remember I’m a guide and avalanche forecaster, not an electrical engineer. I can’t offer definitive answers on the more technical questions, but I can give you my perspective as an avalanche practitioner and pass on what I’ve learned by talking to experts in the field. 

Question 1: Does airplane mode make any difference?

On my phone, airplane mode turns off some but not all transmit/receive functions. When airplane mode is on, Wi-Fi and cell signals are turned off but:

·        Bluetooth remains active; and

·        I’m still getting positional and tracking functionality in mapping apps, so GPS remains enabled. 

Given this, it’s my opinion that the only way to eliminate potential active interference from your phone is to turn it off. 

We know turning off isn’t realistic or practical in all circumstances. So, if you decide not to power down completely, then turn off functions you don’t need (e.g., Bluetooth) and using airplane mode are at least a partial solution and it’s probably better than nothing. 

Question 2: What about heated clothing, heated googles, googles with fans?

Anything that uses electricity is a potential source of interference. When these items are turned on, you’re dealing with active interference. And even when turned off, the battery, metal components, and wires in the equipment are potential sources of passive interference. The more wiring and the more current being used, the more I worry about interference. And anything that surrounds or covers the transceiver is a no-go.

So, heated jackets—nope; not ever in any circumstances. Heated gloves must be turned off and stowed in your pack when searching. Same for goggles. Heated socks should be turned off and be careful to keep your distance when you’re in fine search mode, with your transceiver close to the ground and near your feet.

Question 3: Many snowmobiles have Bluetooth. Will that make a difference?

Even without Bluetooth, sleds are a source of active interference when they are running. Electricity is flowing and that creates an electromagnetic field. 

And yes, a sled with Bluetooth adds another dimension to the problem. I’m not sure how Bluetooth works in these sleds. If the Bluetooth still functions when the engine is off, then you need to figure out how to turn it off or you need to keep it 25m away from the search area. 

Electronic devices on newer sleds may cause interference. 

If, like other electrical activity, Bluetooth gets shut down when you turn the machine off, then you are just dealing with a rather big chunk of metal which is, of course, a potential source of passive interference. 

Question 4: Are some brands of transceiver better than others in terms of interference? 

I’m not aware of any research or test results that indicate a difference in transceiver brands regarding this issue. Given that all transceivers use the same frequency and the same fundamental principles to send and search for signals, I suspect there’s little or no difference between brands. 

If you’re concerned, I suggest contacting the manufacturer to see if there are brand-specific features or functions for managing/mitigating interference, then choosing a transceiver that you’re most comfortable with.

 Question 5: What about medical devices?

Any medical device that has metal or foil components must be considered a potential source of passive interference. Any medical device that has a battery, uses electricity, and/or sends/receives signals is a potential source of active interference. 

Now, with medical devices we’re solidly in the realm of balancing risks. Obviously, you don’t want to turn off or disable a device that’s keeping you healthy and alive. So, you’ll need to figure out how to mitigate interference while using these devices.

I strongly suggest you check owner’s manuals or contact the manufacturer of your medical device and transceiver for advice. Barring contrary advice from the manufacturer, at least keep your transceiver a minimum of 20cm away from your medical device when in send mode and 50cm away in search mode. And learn the strip search technique in case you do end up in a situation where you can’t fully mitigate interference.

If you are getting signs of interference near power lines, I can’t think of any way to mitigate this other than learning the strip search technique. Same goes for buildings and electrical machinery, motors, etc. 

 Question 7: Do smartwatches interfere with transceivers?

I can’t think of any situation where a smartwatch is an essential piece of equipment, although I admit I’ve never used one so perhaps I’m wrong. My advice is turn off your smartwatch and stow it in your pack, if not at all times, then for sure when searching.

I completely forgot to discuss packs and airbags in my original article. So, here’s my take.

All packs are potential sources of interference—there could be metal components (e.g., buckles or stays) and almost certainly there are metal contents (shovel, probe, etc.). No matter whether it’s an airbag or not, your pack is an essential piece of gear. In most companion rescue situations, dumping your pack isn’t a realistic option. 

Airbags driven by a compressed gas canister can be treated as a source of passive interference. Figure out where the metal components are (remember there are probably metal parts or wires involved in the trigger mechanism) and wear your transceiver in a way that maintains at least 20cm separation from those components. Battery-powered, fan-driven airbags require the same 20cm separation when in send mode. 

Things change when in search mode. If you’re using a compressed gas airbag, it is a source of passive interference, and you need to keep your transceiver at least 50 cm away. You can usually achieve this by holding your transceiver in front of you and on the opposite hand from an airbag trigger.

A battery-powered, fan-driven bag is a different story. Like any other electrical device, it’s a potential source of active interference. You must decide whether it’s safe to turn the airbag off while searching. If yes, then do so and use the same 50cm separation as described above for passive interference. But if you’re in a situation where you don’t feel you can turn it off, you’ll need to mitigate as best you can. Change where you hold the transceiver while searching, shift the pack a bit to increase the distance from the transceiver as much as possible, and, if all else fails, use strip search techniques. 

 Airbags and radios can both be sources of interference. 

Question 9: How do I test for interference?

This is a highly complex problem that defies a simple ‘one size fits all’ approach to testing, given the huge array of potential connections and interactions between devices and signals. The experts I consulted were very reluctant to consider testing as a solution to this problem, saying that there’s no surefire way to provide definitive answers. 

With no comprehensive guidance on how to test effectively, my real-world strategy revolves around preparation, awareness, and backup search strategies. Here is my approach:

1.      Turn non-essential devices off and stow them in my pack. Maintain adequate distances between transceiver and interference sources.

2.      Stay vigilant. If I see strange or unexpected behaviour when working with a transceiver, recognize problems early and assume it’s interference.

3.      Mitigate the source(s) of interference.

4.      Use strip search techniques if adequate mitigation isn’t possible. 

If you go to the International Snow Science Workshop archive and put the word interference in the search field, you’ll find links to some historical papers on the topic. A Google search on “avalanche transceiver interference” will turn up some additional information. And the coming issue of The Avalanche Journal has an article on interference that contains some test results.

 Question 10: I’m wondering if a Faraday pouch or lining my phone pocket with Faraday tape would block the interference caused by the phone signal?

Faraday tape and fabric is intended to block electromagnetic radiation. In theory, keeping your devices in a Faraday bag or pocket would stop potential active interference. But this would also block incoming calls and communications with other devices. Similarly, a navigation device would not be able to receive GPS signals so tracking functions won’t work while the device is in a Faraday enclosure.

So, while there are probably some potential benefits for specific scenarios, you’re going to have to live with limitations. If you do decide to go this way, remember that the Faraday enclosure is an additional source of passive interference and will almost certainly be highly effective in blocking transceiver signals if you’re not careful. Just like you keep it away from other metal or foil objects, be sure to keep your transceiver away from a Faraday pouch or pocket.

 Forecasting supervisor, James Floyer, checks his phone before turning it off and stowing it away from his transceiver. 

Interference and Avalanche Transceivers Part 2

We’ve long known that transceiver signals can be affected by metallic and electronic items. In our increasingly wired world, where we head into the backcountry with phones, video cameras, satellite communication devices, and more, this subject has become more important. With this in mind, I did some homework. 

A transceiver search can be quite challenging. Make your life easier by eliminating potential sources of interference. 

First, I discovered that interference is generally described as being either “passive” or “active.” Passive interference blocks the transceiver’s signal, and it happens when the transceiver is too close to items made of metal or foil. I’ve often seen transceivers produce an error message or alert when someone was wearing it near or under a pocket that contained a candy bar with a foil wrapper or a metal water bottle (ok, truly, it was a whisky flask—but you get the idea). 

One of my most memorable experiences with passive interference involved a regular one-metre transceiver check that showed no problems, but at about 10 metres the signal completely disappeared. Eventually we determined there was a layer of heat-reflective foil in the person’s jacket. When they took off the jacket the problem disappeared. (Yes, we did find them another jacket, so they didn’t have to ski in their underwear).

Active interference disturbs the transceiver’s signal. This occurs when the transceiver is too close to devices that use electricity, carry an electrical current, or transmit or receive electronic signals. The result of active interference is like static on the radio or a pixelated TV picture. The signal is distorted, which makes the transmitted information hard to understand.

These days, we’re surrounded by items that can present active interference. Heated jackets, gloves, and socks all have wires carrying an electrical current. Add mobile phones, GPS units, and satellite-enabled communications devices to the list. And don’t forget when we link our devices using a wired connection (attaching headphones to our phone) or wirelessly (pairing a GPS unit or SOS device to our phone via Bluetooth). All of these and more are potential sources of interference.

Interference—both passive and active—affects a transceiver’s send and search modes. Mitigating interference is not complicated while you’re in send mode. Keep all sources of interference, passive and active, at least 20 cm away from your transceiver. I personally shoot for 30 – 40 cm. 

This means making some effort to ensure your transceiver stays in place, so it can’t get closer to any gear that might cause interference. This may require some modifications to your transceiver harness. I keep my transceiver on my right hip, in an inside pocket with a zipper closure. Anything I need ready access to, like my radio, goes in my top left jacket pocket. Electronics that don’t require quick access, like my GPS, SOS device, and phone, all go in the top pocket of my pack, on the left side. 

If you are shooting POV video, wear your camera on your helmet or use a stick. A chest harness is a no-go (where I ski a chest harness is useless anyway—all you see is white all the time). Jackets with a heat-reflective foil liner are also a no go. Be careful—sometimes the foil is between the jacket shell and liner so it may not be visible. Heated socks are probably okay but heated jackets are definitely not. Heated or foil-lined gloves should be avoided because the transceiver is in your hand when you’re searching. If you use these types of gloves, they need to be taken off and stowed away during a search, so you better have a back-up pair. 

When in search mode, you’ll need to increase the distance between your transceiver and sources of passive interference to 50 cm. This is not as big a deal as it might seem. Simply taking your transceiver out and holding it in front of you will likely be adequate. If you wear an electronic watch, you’ll need to take it off and store in your pack while searching. 

The electrical engineers I talked to were most concerned about active interference in search mode. There are so many types of devices operating on various frequencies, the experts I consulted felt there is no realistic way to test all those combinations and configurations to come up with a standard approach to solving this problem. 

The consensus advice was this: When it comes to active interference—items with an electrical current, or any type of signal like Wi-Fi, Bluetooth, GPS, or phone—the best approach is to turn these devices off when searching. Even when not in active use, many devices are actively searching for or receiving information, which can interfere with your transceiver. Even sleep mode, airplane mode, and other means of restricting functions does not guarantee your device is fully dormant, and interference remains possible. 

In practically all cases, when you turn off an active source of interference it then becomes a passive source of interference and needs to be kept 50 cm away from your transceiver in search mode. So, after you’ve turned everything off, stash them in your pack before you begin searching. Turn off your heated socks and remember that in the fine search stage, when your transceiver is near the ground (and your feet), be aware that you’re getting close to the wiring and batteries. 

Remember to turn off your heated socks so they don't cause interference during the fine search.

However, some electronics may be essential in some situations. You may want to use a phone or a radio to call for help or communicate with other rescuers. You’ll almost certainly want to send an SOS from your emergency messaging device, and you may need to provide information to the recipient of your SOS message. 

If you’re using a device to communicate while searching, the advice I got was to keep that device at least 25 metres away from the searching transceivers. In a best-case scenario, you would have enough people on scene to allow someone to move away from the search to handle any messaging. If that’s not possible and it’s essential you use a device, consider stopping your search, do what you need to do, then turn the device off and stash it before resuming your search.

Keep vehicles, snowmobiles, and other machinery at least 25 metres away from search areas. These are generally packed with electronics, have lots of electrical components, and are going to cause significant problems if they are too close, especially if they are running.

What’s essential and what’s not essential will vary from one situation to the next. In a place where there’s no cell coverage and you are out of range for two-way radio communications, mobile phones and radios may be non-essential and you’ll rely on your emergency satellite communications device. If you’re using your phone or two-way radio to coordinate an effective rescue and are getting help by these channels, then maybe your sat device is non-essential and can be turned off.

Interference commonly manifests as intermittent transceiver signals, distance indicators changing for no apparent reason, inconsistent directional arrow displays, and audible tones fluctuating even when you’re standing still. Ultimately, if you experience any of the above or other unusual transceiver behaviour, especially when in search mode, you should suspect interference and take steps to mitigate it. Personally, if I get any weirdness while searching, my first response will be to turn off EVERYTHING and stash it.

If all else fails, make sure you are fully familiar with micro-strip search patterns. If you’re having trouble locating a signal, micro-strip searching will resolve most situations, not only interference but also other issues like multiple transceivers buried in proximity. If you don’t know what a micro-strip search is, take a Companion Rescue Skills course.

Here are some common sources of interference:

Heat reflective clothing (jackets, gloves, mitts)

Magnets of any kind, including those used in closures for zipper flaps and pockets. 

Satellite communications devices: Satellite phones, GPS units, and SOS/emergency communications devices

Watches, especially GPS and smart watches

Heated clothing (jackets, mitts, gloves, socks)

Medical devices (pacemakers, insulin pumps, etc.)

Mitigating Avalanche Transceiver Interference

Chaque année, à ce temps-si, nous commençons à réfléchir aux effets que le réchauffement aura sur le manteau neigeux. Historiquement, le mois de mars est le plus mortel pour les avalanches, probablement en raison d'une combinaison du manteau neigeux et de facteurs humains. Le premier gros échauffement peut faire bouger les choses, surtout lorsque nous avons des manteaux neigeux froid avec des couches faibles persistantes comme celles actuellement en jeu dans tout l'ouest du Canada. En plus des conditions d'avalanche délicates, des journées plus longues et plus chaudes peuvent conduire au «syndrome du ciel bleu» où nous sous-estimons potentiellement le risque et laissons tomber nos gardes.

Les prévisions météo on attiré l'attention de l'équipe de prévision d'AvCan. Au fil de la semaine, nous assisterons au premier réchauffement significatif de la saison, dans certaines régions, accompagné de précipitations modérées à fortes. Le timing, la sévérité et l'étendue ne sont pas encore entièrement certains, mais à court terme, il semble que le plus grand réchauffement se produira dans le sud-est de la Colombie-Britannique et le sud de l'Alberta. Ceci dit, le réchauffement sera une préoccupation dans toutes les régions - en particulier celles avec des couches faibles persistantes.

Dans les prochains jours, nous examinerons de près les prévisions météorologiques, et toute préoccupation particulière sera reflétée dans nos prévisions d’avalanches quotidiennes. Mais il y a quelques thèmes généraux à considérer à cette période de l'année, quelle que soit votre région ou la journée où vous envisagez de voyager dans l'arrière-pays:

•	Réduisez votre exposition au terrain d'avalanche lorsque la température augmente rapidement. Soyez encore plus prudent si les températures sont au-dessus de zéro.

•	Évitez de vous déplacer sur ou sous des pentes exposées au soleil. Cela inclut de garder un œil sur les pentes au-dessus de vous, en particulier le matin lorsque les altitudes supérieures reçoivent le soleil beaucoup plus tôt que le bas près du fond de la vallée.

•	L'importance de l’orientation du versant devient plus critique. Les pentes exposées au sud sont plus sensibles aux effets du réchauffement, tandis que les pentes exposées au nord restent plus froides.

•	La planification de l’itinéraire est de plus en plus importante; commencez tôt quand il fait frais et terminez tôt avant qu'il ne fasse trop chaud.

•	Soyez conscient du terrain d'avalanche en surplomb; les avalanches sont plus susceptibles de courir jusqu'au bout de leur trajet à cette période de l'année.

•	Les petites avalanches ou les chutes de corniches peuvent déclencher de grosses avalanches là où il y a des problèmes de plaque ou couches faibles persistantes profondes.  

•	Utilisez le pouvoir des décisions de groupe. Donner une voix à chaque membre aidera les groupes à prendre de meilleures décisions plus sûres. Dites-le si vous n'êtes pas à l'aise ou si vous pensez qu'il existe une meilleure option qui pourrait nécessiter un peu plus d'efforts.

Des changements soudains de la météo sont prévus dans la semaine à venir. Attendez-vous à ce que cela complique les conditions d'avalanche.

Blogues

La chaleur monte : un nouvel échauffement entraîne une augmentation du risque d’avalanche

Interference and Avalanche Transceivers Part 2

Mitigating Avalanche Transceiver Interference

Il est temps d'envisager le réchauffement