乗鞍岳・標高2640m、暴風域でのイグルー泊
春の気圧配置で、すごい風の日に乗鞍岳を独自ルートで山越えしました。相棒の長年の設計ラインで鋭鋒・烏帽子岳に直登する尾根です。美しい針葉樹林を10時間近くラッセルして山頂から火山台地に出たところで暴風域に入りました。テント（もっていないけど）ではぶっ飛ばされる事必定。
風で屋根が落とされてできない→スキーで屋根掛け
翌朝撮影。この暴風では隙間は塞げず吹き込んだ雪はツエルトとの間を流れ落ち、側面から溜まった。屋根にスキーの先端が見える。
スキーを引っこ抜いてもブロックはくっついていて屋根は落ちなかった
乗鞍スカイラインはアイススクリューが要るほどの青氷。吹き溜まりにノコギリの入る積雪を見つけ、そこにイグルー作製開始。ブロックは下一段は切り出せるがその下は青氷。広くブロック供給場を設けて運んで組んでいく。三段目くらいで長いブロックを屋根かけすると、眼を離した隙に風で落とされる。落ちて皆半分に折れてしまう。3回くらい繰り返し落とされて、スキーとストックを梁にする方法に切り替える。あっという間に屋根完成。
風上側に二重にブロックを積んで隙間ふさぎ
いつもみたいに悠長に隙間ふさぎをできないので、風上側にはもう一重外側に壁を載せて二重の厚さにする。それでもこの地吹雪の粉雪は、隙間から吹き込むやつだ。前に富士山でやられた感じだ。相棒は始めブロック取りに勤しんでいたが、そのうち顔面にシュカブラができてメガネがアウト。目潰しの雪つぶてで、風上を見られない。ツエルト被って待っていてもらう。そのツエルトもぶっ飛ばされないようにかぶるのがまたタイヘン。
内張りのツエルトはベルヌーイの定理でピシッと張り付く
中はやっぱり隙間から吹き込みまくりだ。でも中でツエルトを被ったら不思議なことが起こった。ツエルトが、固定もしないのに壁に張り付いて落ちて来ない。風で流速の早い外部はイグルー内よりも気圧が下がるせいだろう。飛行機の翼が上面の流速に吸われて浮き上がる「ベルヌーイの定理」である。中学生の頃から航空工学好きで知ってるんだ。ベルヌーイは翌朝まで続いた。でも風、弱まってほしかった・・。
イグルーの中は結局雪まみれ。でも風は音だけだ。
壁とツエルトの間に入り込んだ吹込み雪が、外側からずんずん攻めてきた。両側は雪がつもり、吹き込んだ雪が寝袋の上に積もり、やがて体の下にも落ちて体温で溶けて冷たい水たまりになり、一晩中ブルブルだ。でも死ぬほどじゃない。風は時折ドカンドカンとパンチのように壁を叩く。壊れたらどうするかシミュレーションはしてある。でも壊れなかった。
膝の上でストーブを焚き、ミルクティーを何杯も飲んで晩飯も朝飯も終わり。明るくなっても風は止まず。ドボドボに濡れた寝袋をザックに突っ込んで、樹林限界まで鼻をつまんで脱出した。視界があるってありがたい。強風晴天のなか、安全圏へ下る。計画は半分だったけどあの風では仕方ない。なんとかやり通せてきた満足が大きい。
風が強く積雪が少ない場所のイグルー
同じような状況は以前富士山で体験した。積雪が少ないので貧相なブロックの上、隙間から転がりまくったザラザラの雪粒が絶え間なく吹き込む。その時のメンツは「イグルー懲り懲り」に。今回は内側にツエルトで快適とまでは言えないがなんとか凌いだ。もっと大きいタープならば外側に被せて張る手もある。でも、固定する雪面が青氷なので、スクリューが要るしあの風ではちぎれて飛ばされそう。こういうところに泊まらないのがベストだけど、注文通りに行かないのが山だ。そうなったら手持ちでやりくりするしか無い。
Igloo Night in the Storm Zone at Norikura-dake (Elevation 2,640m)
Crossing Norikura-dake on a Unique Route in Fierce Winds
During a spring weather pattern with intense winds, I traversed Norikura-dake via a unique route. My partner’s long-established route design follows a ridge leading directly up to the sharp peak of Eboshi-dake. We spent nearly ten hours breaking trail through beautiful coniferous forests before reaching the volcanic plateau at the summit, where we entered the storm zone. A tent (not that we had one) would have been blown away for sure.
Roof Collapsing in the Wind → Ski Roof Construction
The Norikura Skyline road was covered in blue ice, requiring ice screws for traction. We found a snowdrift with packable snow deep enough for a saw to cut through, and we began constructing our igloo there. The first row of blocks was easy to carve, but beneath that was solid blue ice. We widened the block supply area, transported them, and stacked them.
Around the third row, we attempted to place long blocks as a roof, but the wind knocked them down the moment we looked away. Every time they fell, they snapped in half. After this happened three times, we switched to using skis and poles as beams. That worked like a charm, and the roof was up in no time.
Double Layering the Windward Side to Seal Gaps
Unlike usual, I couldn’t afford to leisurely fill in the gaps. On the windward side, I added an extra exterior wall for a double-thickness defense. Even so, the powder snow carried by the ground blizzard kept infiltrating through the cracks—just like what happened to me on Mt. Fuji before.
My partner was busy collecting blocks at first, but soon, his face was covered in frost formations (sastrugi), and his glasses became useless. The wind-driven snow kept striking his eyes, blinding him from looking upwind. I had him wait under a bivy sack, though even that was a struggle to keep from being blown away.
Bivy sack Sticking to the Wall Thanks to Bernoulli’s Principle
Inside the igloo, snow was still blowing in from the gaps. But when we wrapped ourselves in a bivy sack, something curious happened—it clung to the walls without any support. The fast-moving wind outside created lower pressure compared to the inside, making the tarp stick to the surface. It was a real-life demonstration of Bernoulli’s principle—the same aerodynamic effect that makes an airplane wing generate lift. I’ve been interested in aeronautical engineering since middle school, so I recognized it immediately.
Bernoulli’s effect lasted until morning. But I sure wished the wind would die down sooner…
The Igloo Filled with Snow, but at Least the Wind Was Just Noise
The snow that blew in between the walls and the bivy sack kept creeping inside. Snow piled up on both sides, covered my sleeping bag, and eventually fell underneath me, melted from my body heat, and turned into a freezing puddle. I shivered all night, but it wasn’t life-threatening.
The wind occasionally slammed against the igloo like a powerful punch. I had simulated an emergency plan in case the walls collapsed, but fortunately, they held.
I lit my stove on my lap, only drank multiple cups of milk tea, and skipped both dinner and breakfast. By morning, the wind was still howling. I stuffed my soaking wet sleeping bag into my backpack, had to bite the bullet and push through the storm to reach safety.The visibility was a blessing. Under clear but violently windy skies, we descended to safety. The trip was only half of what we planned, but given the conditions, that was inevitable. More than anything, I felt deeply satisfied that we managed to push through.
Building an Igloo in Strong Winds with Minimal Snow
I had encountered similar conditions before on Mt. Fuji. There, with little snow, we had to stack flimsy blocks while an endless stream of granular snow particles tumbled through the gaps. That time, my companions swore they were done with igloos for good.
This time, the bivy sack inside made it somewhat bearable, though certainly not comfortable. A larger tarp might have helped if we had stretched it over the exterior, but anchoring it on blue ice would have required screws, and the wind would likely have shredded it anyway.
Of course, the best option would be to avoid camping in such places. But mountains don’t always follow orders. When faced with the unexpected, you just have to make do with what you have.
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