Yesterday I posed the query, “What are the circumstances that promote the expansion of Floor Hoar”. There have been many appropriate solutions. Let’s dive just a little deeper into the circumstances and take it past the extent 1 understanding.
In my AIARE 1 avalanche programs I educate college students to recollect the three “C’s” that promote the expansion of floor hoar.
Cold- Unsurprisingly it must be under freezing (32°F, 0ºC) for floor hoar to type.
Clear- The mechanisms that drive the expansion of floor hoar require fast radiative warmth loss from the snowpack. This solely happens on clear nights. Cloud cowl has an insulating impact on the earth and just about prevents the kind of warmth loss wanted for this course of to happen.
Calm- Floor hoar crystals, as soon as shaped, are susceptible to average wind speeds. The ice varieties have little or no horizontal power, and in case you discover a pocket of respectable sized floor hoar you’ll be able to check this simply by getting near the crystals and giving them a hearty blow of air from your personal lungs.
That’s just about the extent 1 sort data I instill in my college students. Now let’s dive deeper into different necessary issues that contribute to the snowpack’s capacity to type floor hoar.
Humidity & Dewpoint– Principally floor hoar is winter’s equal of “dew”. There should be a excessive degree of humidity (over 70%) within the air proper at floor degree.
Air motion– Because the crystal development of floor hoar is eradicating vapor (moisture) from the air because it grows that moisture should be changed for the crystals to continue to grow. The air motion required is so gentle that an observer would file “calm” for wind velocity.
Temperature Inversion/Gradient– A robust inverted temperature gradient is required proper on the snow floor. This gradient is greatest achieved by the fast radiative warmth loss situation promoted by chilly clear nights. Even a lightweight breeze will take away this floor degree inversion and inhibit development.
Now that we’ve gotten the sciencey climate stuff out of the way in which let’s get into some sensible terrain issues for the subject.
Sheltered/Lee– Since we all know any noticeable wind inhibits floor hoar development we will look forward to finding it in areas shielded from the wind, i.e. lee.
Cover– As a result of floor hoar requires fast radiative warmth loss any tree cover will inhibit development. Floor hoar is commonly present in clearings that aren’t obstructed by any tree cowl.
Side– It’s affordable to imagine northern features could also be extra prone to develop floor hoar as they’re colder features. In areas with predominant west winds (White Mountains) you will have extra luck discovering floor hoar in your North to East features.
Elevation– Since above treeline circumstances not often promote the expansion of floor hoar this weak layer is extra widespread under treeline, and in the appropriate circumstances center elevations.
Slope Angle– Floor hoar has what is named “anisotropic” construction. What this principally means is it’s robust on the vertical axis and really weak on the horizontal axis. This property is the primary cause it’s such a reactive weak layer when buried by new snow. Its capacity to resist gradual will increase in load till it reaches its breaking level is why in sure snow climates it’s the first situation for human triggered avalanches. It’s also why you wouldn’t count on this in steeper begin zones. Within the uncommon case of this forming on a 40 diploma begin zone of an alpine gully any cohesive snow that falls on high of it is going to shortly overwhelm its horizontal power. Discipline observations present it is a widespread layer for remotely triggering avalanches on flat terrain. Twenty 5 diploma rollovers are additionally generally triggered on floor hoar.
Slope Form– Analysis exhibits that concave slopes inhibit development. That is as a result of diminished radiative warmth loss on concave slopes. Conversely, convex slopes might even see extra progressive development as they’ll speed up fast radiative warmth loss and a stronger floor left temperature gradient. But another excuse convexities on a slope are widespread set off factors.
Proximity to Water– As a result of the bottom degree humidity wants replenishment you’ll be able to usually discover this rising subsequent to creeks, streams, and steam “vents”. These “vents” are fairly cool, even on a damaging temperature day in case you stick your thermometer in considered one of them you’ll discover the air temp hovering round freezing (32°F, 0ºC).
Snow Local weather– The prior talked about climate circumstances are most typical in Continental (Rocky Mountain) snow climates. Floor hoar can, and does, type in any snow local weather, but it surely’s most prevalent in Continental snow climates.
Native Examples– I’ve discovered just a few locations in Mount Washington Valley that I take into account “floor hoar farms”.
Probably the most dependable spot I’ve discovered is simply south of the trestle minimize on the high of Crawford Notch the place some sheltered steam vents on the west aspect of the tracks usually have floor hoar crystals round them. Sadly the railroad is lively this winter and no trespassing indicators are posted so I don’t suggest heading there.
The sphere simply exterior the AMC Highland Heart has had some good floor hoar shows over time by they’re normally brief lived as calm clear climate doesn’t final lengthy on the high of the notch.
The bottom of the Cog Railway has small slopes which have produced a few of the largest floor hoar crystals I’ve ever seen in individual, some as much as 4 centimeters in measurement!
I’ll usually discover small pockets on the perimeters of the Tuckerman Ravine Path however the spot on the east aspect of Mount Washington I’ve had probably the most luck is on the Summer season Lion Head path, proper because the path steepens and crosses an outdated avalanche path there are a pair small steam vents on the left aspect which have a transparent view of the sky (due to outdated avalanche exercise).
Abstract– Properly that’s about it for my mind dump on floor hoar. Hope you’ve discovered one thing new about what is probably going my favourite sort of ice formation. For extra studying you’ll be able to try The Avalanche Handbook. It’s the place most of my data is derived and a fantastic useful resource for many who actually wish to dive into the trivia of avalanche formation.
Snow Visa Giveaway
Be taught extra about this progressive snow security device right here and enter to win one free of charge by clicking this hyperlink! Contest ends on at 8PM EST on 12/24/2023!
See you within the mountains,
Northeast Alpine Begin
Affiliate hyperlinks above assist this weblog. Purchases made by these hyperlinks earn me a small fee at no extra value. In the event you discovered this content material to have worth take into account a small donation through Venmo or PayPal to assist this weblog. Thanks.
