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Thursday, Feb. 7, 2002
Precipitate beauty of nature's own ice sculptures
By MARK BRAZIL
"The sky has holes to let rain in; the holes are small, that's why rain is thin." So wrote the zany British comedian Spike Milligan. Rain. Some hate it; I love it. It's a gift (thin though it may be) from the heavens.
I have traveled in some of the most arid regions on earth and despite encountering some wonderfully adapted plants and animals, I prefer regions prone to precipitation any day. Instead of baked, hard ground and soils akin to sand or rock, I prefer softer soils, richer loams on land that has soaked up falling water.
Precipitation in its many forms is just a passing phase in the cycle of water that takes it through evaporation, then condensation, precipitation, absorption and runoff, circling in a continuous exchange of moisture through the air, land and oceans.
From gentle, scented spring rain redolent of rich soils to the "cats and dogs" of a torrential downpour; from the almost foglike fine spray of Japanese kiri-same to the air-filling deluge of a south Indian monsoon; from the fine, dry powdery crystals to huge, wet sticky snowflakes . . . all are some form of precipitation.
And not only does precipitation vary in form, it varies in its formation and its effects. In the long-baked Kalahari Desert, I watched with astonishment as unprecedented downpours northwest of Namibia brought deeply flowing water to the usually dry bed of the Auob River. Yet just a few meters from the new flow, the ground remained hard and desiccated.
At the opposite extreme, in southern Japan, I have seen moist soil come loose from the steep slopes to form mudslides in a torrent of rain -- the already saturated soils could absorb no more.
Precipitation begins as gravity draws water droplets down from the clouds. Droplets of water vapor are generally so small that air currents and air resistance are sufficient to keep them aloft despite the pull of gravity.
They measure a mere 20 microns (0.02 mm) in diameter. Turbulence within clouds sets these droplets on a bouncing and colliding bumper-car ride, but, unlike the fairground cars, these droplets don't just bounce off each other, they collide and merge, growing larger at each bump.
By the time water droplets have increased in size a hundredfold, to around 2,000 microns (2 mm) in diameter, air currents and resistance can no longer support them. As they fall from their home cloud, they collide with even more droplets and continue to grow through this process of coalescence, eventually reaching the ground as rain.
This is not the only formation process for precipitation, though. A second process was elucidated by Swedish and German scientists of the 1930s and is named after them -- the Bergeron-Findeisen process. In thick clouds, super-cooled water droplets and ice crystals may coexist. The ice crystals rob water molecules from the droplets and grow rapidly until they fall.
These crystals also continue to grow through coalescence, like the raindrops, but, depending on the temperature below the clouds, they may remain frozen and fall as snow or melt and fall as rain.
The precipitation that we experience on the ground, that may have us reaching for our umbrellas or our winter parkas, depends first on the process up in the clouds and then on the temperature of the layer of air between the clouds and the ground.
At moderate or warm temperatures, coalescing water droplets may form fine drizzle or light to heavy rain, but if the temperature below the cloud is low, then the most treacherous precipitation -- freezing rain -- may fall.
Freezing rain forms an attractive glassy surface on twigs, branches and the ground, but it is the bane of birds and plants. The crystal-clear layer coats leaves and branches, locking away the food of many birds from reach. Its weight, meanwhile, can crush delicate plants, entomb insects and break branches from even sturdy trees.
Freezing rain is not much fun for drivers, either. Once, soon after a 360-degree spin on glazed ice on a south German autobahn, I watched in amazement as children ice-skated down a suburban street: There, the frozen layer was more than a centimeter thick and like an ice rink.
When ice crystals, rather than water droplets, form in clouds, and when the air between cloud and ground is also cold, then dry, powdery snow falls. At slightly warmer temperatures, snowflakes are larger and prettier (a joy to examine under a hand lens or microscope. If you don't have either, try looking at them up-close through the "wrong" end of your binoculars). As the temperature rises still further, they form increasingly wetter flakes, then finally rain.
Japan experiences extraordinary climatic extremes simultaneously because of its great length and range of altitudes. At the same time spring-like rains dampen the subtropical islands of the south, the worst of snows (large wet flakes verging unpleasantly on rain) may fall in central Honshu and powder snow, fine as white sugar crystals, may drift across the north.
Frozen lakes, frozen rivers and sea ice all occur during the same season in the same country that sports warm-water corals, mangroves and sharks.
Coming from the rainy isles (the United Kingdom), I thought I knew precipitation from A-Z, but I hadn't reckoned with either shimobashira or nyoronyoro. Presumably neither is unique to Japan, but just beyond my own previous experience.
I first encountered shimobashira in the Tanzawa mountains southwest of Tokyo and immediately conjured the image of a seamstress dropping a case of glass needles on the dry ground. After getting down on my hands and knees to inspect these needles up-close, it was clear that the scattered heap had been disturbed. Nearby, I found their original form: ranks and rows of curving, curling, needles standing tall in the dry soil.
I have found them beside many a mountain trail since, in both Honshu and Hokkaido, bristling pins close-packed and tall in early morning shade but readily collapsing as the day warms. They seem only to form under frosty conditions when the air is very dry.
Nyoronyoro is incredible in a different sense. When first invited to view this marvel, I had no expectations. After skiing down a long, narrow valley cut into the lower flanks of Mount Tokushunbetsu in Ohtaki, Hokkaido, I was directed to what, at first sight, appeared to be merely a cliff overhang. It turned out to be a deep cave, its ceiling coated with hundreds of bizarre ice sculptures.
What happens is that precipitation soaks into the soil up-slope from the cave, penetrates its ceiling and emerges as drips and drops of water. It falls and freezes there into ranks of pendulous, icy stalactites and stalagmites.
Dry winds penetrating the cave had sculpted some into fine flutes and thin blades, but some joined, forming pillars from ceiling to floor. Named nyoronyoro, for Tove Jansson's "Moomin Valley" character, these strange writhing ice sculptures, formed afresh each year, make the Sapporo Ice Festival sculptures seem dull and rigid in comparison.
On my most recent visit, a surprising warm snap had allowed warm air into the cave, the ceiling was almost devoid of ice crystals and almost all the ice stalactites had fallen or melted on the cave floor. The icy columns had grown bulbous and were flat-topped with wet drips. Staring down into these columns of clear ice was like staring into an endless distorting tube, a motionless kaleidoscope of temporarily trapped precipitation.
E-mail Mark Brazil at firstname.lastname@example.org