snow2.jpg (4026 bytes)Japan - The Snow Crystal Tour, Part 3
-- by Kenneth G. Libbrecht,   January, 2002
Hoarfrost at Lake Kussharo
   From snowy Asahikawa and the Snow Crystals Museum we journeyed east to Lake Kussharo, the largest lake in central Hokkaido.  It snowed a lot along the way, and the view out the train window was constantly changing, partly because the weather changed so much with location.  The first picture below shows the scenery during a particularly heavy snowfall.  Once again a view reminiscent of my youth.
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Lake Kussharo is located in Akan National Park, at an elevation of 1000 meters, and serves tourists mainly as a summer resort destination.  One reason for visiting Kussharo in winter is to be snowed on while sitting in an outdoor spa, or onsen, since the lake is famous for its many natural hot springs.  Kussharo sits in the middle of a large caldera, with quite a lot of residual geothermal activity.
   Although much of the lake freezes over in winter, the runoff from hot springs keeps some patches unfrozen even in the coldest weather.  This attracts a substantial swan population in winter, including the Whooper Swans shown above (first picture).  The hot springs also provide some spectacular ice crystal displays, something you won't find mentioned in the tour books.  The second picture shows the scene near a popular onsen.   The natural hot spring has been plumbed to provide a continuous flow of hot water into this bath, right on the lake shore, which subsequently drains into the lake.  You can see in this picture how water vapor from the bath freezes onto the branches of a nearby tree, covering them with a thick layer of frost.   (You can see in this picture that the swans enjoy the warm water as well.) 
   The third picture gives a nice close-up showing the ice structure on the branches.  In some spots the ice is composed of a conglomeration of frozen water droplets, with little or no faceting to reveal the ice crystal structure.  Most of the ice, however, forms directly from water vapor in the supersaturated air, and thus shows the same kinds of structures as snow crystals.  Ice that forms in this way is called hoarfrost.  There is a lot of hoarfrost in this area because the hot water evaporates readily into the air around the bath.  As this air moves away and cools, it becomes very supersaturated, so the water vapor condenses on any structures it encounters.
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The tree branches were already fairly impressive, but I found the real show was a few meters down from the onsen.   Here the lake was frozen, but some warm and very moist air was apparently making its way under an ice sheet along the shore.  When this finally hit the open air, some beautiful fern-like hoarfrost formed (first two pictures above).  You can plainly see the flat dendritic structure here, indicating that the hoarfrost was formed near -15C (see the Primer for why that is).  The third and fourth pictures above, both showing the same hoarfrost structure from different angles, show that some of these crystals were quite large; the 50-yen coin is about 13 mm in diameter.
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In some spots there was hoarfrost just about anywhere there was a surface that ice could condense onto.  This included the edges of ice plates that had crumpled up along the lake shore (first and second pictures above), and on some pieces of bamboo that happened to be frozen into the lake ice (next two pictures). 
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The close-up attachment on my camera (see Taking Photos) served me fairly well to capture some close-up views of the hoarfrost, as can be seen in the above pictures.  Note that all these pictures were taken fairly early in the morning.  By noon the temperature had warmed up and all these structures had evaporated away.  They apparently form overnight when the conditions are right.
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From Lake Kussharo we traveled southeast to the coastal city of Nemuro, and to Cape Nosappu, the easternmost point of Japan.  This brought us out of the snowy part of Hokkaido, and this concludes our Snow Crystal Tour of Japan.  I am most indebted to my family for coming along on this adventure, and for being genuinely excited about going to a remote and frozen corner of the globe for our vacation.  The photo above shows all of us at Cape Nosappu, with the still-disputed Russian Kurile islands visible offshore.  The last two shots came from our quest to see the Stellar's Sea Eagle, one of the world's largest eagles.  The pictures were taken around Nemuro, the latter through my telescope eyepiece.  These beautiful birds live their lives in cold, remote areas; they only come as far south as eastern Hokkaido, and then only in winter.
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