The Perils of Rime Mushrooms

Mountain climber Dmitry Golovchenko captured tremendous video of the February 27 collapse of a “rime mushroom” atop Patagonia’s Cerro Torre. These are bulbs of massively accumulated rime—built up in the freezing of moisture in winds pounding at the peak over time. The mushrooms increase the difficulty of this infamous climb of more than 3,000 meters, but never more so than when their precariousness increases in summer—just when conditions might otherwise seem calm enough for climbing. Here is the video via an Instagram from patagoniavertical, the site of Rolando Garibotti, who co-authored a BAMS article on these infamous mushroom features:

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CERRO TORRE – Escarcha escrachadora / Crushing rime. . Esto sucedió el 27 de febrero a las 11:25am. Si hubiese habido cordadas en la Via dei Ragni, las consecuencias hubiesen sido gravísimas. El video y las fotos las tomó @golovchenko.dmitry, el conocido alpinista ruso. . Los factores que influencian la rotura de los hongos de escarcha son desconocidos, pero parece probable que se comporten como un manto de nieve, y que la combinación de gravedad, calor y humedad, puedan llevar a este tipo de ocurrencias. Esta temporada hay mucha escarcha, que con el calor veraniego, y lluvia en altura, pueden haber sido el disparador. No sabiendo cuales son los factores que afectan las capas profundas de los hongos, es difícil hipotetizar un protocolo, pero parece razonable evitar periodos con la isoterma zero por encima del pie de vía (2300m), o periodos posteriores a lluvia en altura. . Del link en nuestro perfil se puede bajar un artículo sobre la formación de la escarcha en la montaña, publicado en el boletín del American Meteorological Society, escrito por Dave Whiteman, con ayuda de quien escribe. . . . This happened on February 27th, at 11:25am. Had there been any parties on the Ragni Route, the consequences would have been serious. The video and images were shot by @golovchenko.dmitry, the well-known Russian alpinist. . The factors that influence rime mushrooms to result in break off are not known, but it seems plausible that they behave in part like a snowpack, and that the combination of gravity, heat and moisture can result in events like this one. This summer there is ample rime, which combined with heat, and rain at higher altitudes could have lead to this. Not knowing what factors affect the deeper layers of rime mushrooms, it is difficult to hypothesize a protocol to minimize exposure, but avoiding periods with the freezing-line above the base of the route (2300m) would be a wise first step. . Link in our profile to an article about rime formation in the mountains published in the Bulletin of the American Meteorological Society, written by Dave Whiteman, with help from yours truly. . #rime #cerrotorre #patagonia #chalten

A post shared by Patagonia Vertical – guidebook (@patagoniavertical) on Mar 3, 2020 at 6:21am PST

In their BAMS article, David Whiteman and Garibotti introduced rime mushrooms, well known to alpinists, but not previously to many meteorologists:

Rime mushrooms, commonly called ice mushrooms, build up on the upwind side of mountain summits and ridges and on windward rock faces. These large, persistent, rounded or bulbous accretions of hard rime range from pronounced mounds to towering projections with overhanging sides….[They] form when clouds and strong winds engulf the terrain. Supercooled cloud droplets are blown onto subfreezing surfaces and freeze rapidly, making an opaque “hard” rime with air trapped between granular deposits. The mushrooms are most frequent and best developed on isolated summits and exposed ridges in stormy coastal areas.

They showed the distribution of these mountain features around the world.

Thanks to Dr. Whiteman’s Univ. of Utah colleague Jim Steenburgh for bringing the video to our attention via social media. Jim’s own newly published BAMS article features the often well-rimed sea-effect snows of Japan and their similarities to lake-effect snows in the United States. The article explains how the heavy snowy accumulations of crunchy graupel (loose, rimed, large icy particles) in lowlands of the Japanese coast can be quite avalanche prone, too.