Cutting Through the Mystery of Fog

The moody mist is crucial to the survival of some species, deadly to others

  • John Carey
  • Feb 01, 1994
Some of my clearest memories are the foggiest. I mean this literally. Consider one of the scenes etched in my mind from earliest childhood. The place: a remote lake in northern Michigan. On a clear day, the lake is a picturesque beauty. Ripples of blue-green water lap on narrow sandy beaches in the shadow of stately pines, oaks and the occasional white splash of birch.

But venturing down to water's edge on a cool summer dawn is like entering another world-a magical misty world. Dense tendrils of fog rise from the warm water, obscuring the far shore. Even nearby clumps of reeds vanish in the mist. The fog sharpens my senses and unleashes my imagination. In the mist, the lake could be a giant sea. Ordinary trees are transformed into towering giants that disappear skyward in a watery veil, their height limited only by my mind's vision. The eerie wails of the lake's resident loons seem to echo like primeval cries across eons of time.

As often as I've viewed this scene, from early childhood to middle age, its misty vistas have never lost their mystery and magic. But serving as balm to this writer's soul is only a tiny part of the role fog plays in nature and the affairs of humanity. The mist that blows into the deserts of South America and Africa brings life-giving water to entire ecosystems. Fog hovering in valleys offers cooling solace to elk during the American West's hot summers.

Fog can also be a deadly enemy. Migrating songbirds die by the thousands on foggy nights when they collide with tall television transmission towers. The list of human tragedies caused by mist could fill volumes. Take sea disasters, such as the sinking of the luxury ocean-liner Andrea Doria in 1956. The ship suddenly emerged from dense fog near Nantucket, directly in front of the Swedish liner Stockholm. The ensuing collision sent the Andrea Doria to the bottom and the Stockholm back to port with a severely damaged bow. The death toll: 52 people.

All these consequences stem from one of nature's simplest phenomena. When air cools to a certain level, it reaches its dew point (the temperature at which its water vapor begins to condense). The result is a cloud-a cluster of minuscule droplets so tiny that billions would fill a teaspoon. And fog, explains meteorologist Stanley Gedzelman of the City College of New York, "is nothing more than a cloud that touches ground."

While fog is simple, it can arise in a number of ways. The mist that so enthralled me in Michigan, for example, is created by a combination of warm water and cool air. The water warms the air touching the lake's surface and fills it with water vapor. Then, being warmer and less dense than the air above, this moisture-laden layer begins to rise. But as it rises into cooler surroundings, it is rapidly cooled below its dew point. The resulting mist is known as steam fog.

Not only can steam fog enthrall a boy, a similar, thicker type of fog may have helped win the Revolutionary War. On August 29, 1776, George Washington and his army were trapped on the western edge of Long Island by a huge British force. Defeat was imminent. Washington's only hope was to cross the treacherous East River to Manhattan in full view of the British encampment. "Providentially for us," one soldier later recalled, "a great fog arose, which prevented the enemy seeing our retreat from their works which were not more than a musket shot from us." The rest, as they say, is history.

Another important type of fog goes by the dry name of advection fog. As winds blow over relatively warm ocean waters, the air becomes saturated with moisture. Then, near shore, the air suddenly encounters colder waters upwelling from the ocean depths. At Cape Disappointment, at the mouth of the Columbia River in Washington State, the resulting fog appears, on average, for 2,552 hours a year (106 complete days), making it the foggiest spot on the West Coast. The same phenomenon also is responsible for San Francisco's fogs.

The billions of tiny water droplets in fogs like these can supply crucial amounts of water, hydrologist Neil L. In graham of the Desert Research Institute in Nevada has discovered. Ingraham first became intrigued by fog while working in East Africa. Despite a lack of rainfall, he noticed, volcanic peaks rising out of Kenya's Chalbi Desert harbor lush jungles filled with monkeys and baboons. The answer to the riddle, he suspected, was that life-giving water was coming from the dense fog that shrouded the mountains for several hours each day.

Ingraham proceeded to collect samples of fog, groundwater and typical Kenyan rain. He then measured the relative amounts of regular oxygen and its heavier isotope in the water. Since Kenyan fog has more of the heavy oxygen than does rain (fog forms before the heavy oxygen has a chance to drop out of the air), Ingraham was able to determine if the groundwater came from rain or fog. "We found that fog is making a significant contribution," he says.

Later, working at Point Reyes in California, Ingraham demonstrated that much of the water actually inside pine and cypress trees originally came from fog. The water gets into the trees via the normal route, taken up by the roots from the soil. So the results illustrate the key role mist plays in supplying water to the soil. "The implication is that the fog is responsible for the vegetation," Ingraham concludes.

Anecdotal evidence suggests he's right. After the jungle on one Kenyan mountain was burned during tribal wars many years ago, wells reportedly dried up and the trees never grew back. Apparently the fog collected by the trees was crucial to replenishing groundwater. Similarly, botanists believe that some South American forests are completely dependent on fog. Cut them down, and they may never return without the aid of human intervention.

People have learned to simulate the effect of trees by using artificial fog collectors, typically using screens made of a fine wire mesh. The water that condenses on the screen is then funneled into a collecting tank. In one experiment in a tiny village in the coastal Chilean desert, such collectors have been able to pluck as much as 3 gallons of water per person from the air each day.

Fog may be crucial to the survival of some plants and animals, but it can be hazardous to others, particularly birds. One reason misty mornings on my Michigan lake resonate with the calls of loons is that "heavy fog keeps them from flying," says New Hampshire biologist and loon expert Jeff Fair. The birds need a long watery "runway" to take flight, he explains, and fog sometimes makes taking off risky.

Other birds wander off course in fogs. Ornithologist Walter Ellison of the State University of New York recalls hearing sandpipers overhead on a foggy Vermont night, many miles inland from their normal shoreline haunts. Similarly, shearwaters and other seabirds drift closer to land in fog then they would on clear days. For land-bound biologists, says Ellison, "the best way to see seabirds is on a foggy day."

For some birds, modern civilization has made fog a deadly obstacle. On foggy nights, migrating songbirds often become disoriented, even mesmerized, by the lights of tall buildings or towers. Confused, they tend to mill around in great flocks, crashing into unseen guy wires or other structures. The death toll can reach the thousands.

Most creatures' interactions with mists are more benign. Some animals even retreat to foggy valleys to escape the heat of summer, behavior similar to that of people. Yellowstone biologist Sue Consolo Murphy recalls a backcountry reconnaissance through the park last summer. For four days, she and her companion failed to catch a glimpse of the park's abundant elk herds, even though the animals usually are in full view on mountain slopes. Finally, walking through a foggy valley, she stumbled on a herd more than 120 strong. "With the mist in the valley, it was a beautiful scene," she says. "We speculated the fog was providing a cool, comfortable environment for the elk."

Whether the elk appreciate the beauty, as well as the comfort, of mist, is anyone's guess. But for humans, at least, the experience is profound enough to have a key place in art through the ages.

In his research, meteorologist Gedzelman has found that fog periodically has appeared and disappeared in paintings in a distinct pattern. The closer a civilization has been to crumbling, as in Nero's Rome, China's Sung Dynasty or Francebefore the revolution, the more artists tended to obscure their vistas by painting in dense mists. Some of the Sung Dynasty paintings created in the early 1200s, for example, show only mountain peaks or trees poking out of the fog. But with new beginnings-the Renaissance or China after the Mongol invasion-landscapes became clear again. In the periods "when fog was emphasized in art, reality did not want to be seen," Gedzelman theorizes.

Perhaps that insight also explains some of my own fondness for those misty Michigan mornings. Fog can be a veil, a shield from life's harsher realities. Of course, I suppose I should worry about my own mental health if my own fog never lifted. But invariably, the sun emerges, burning away the mist. The loons are again free to fly, and the migrating birds can get back on course. And we are left, once again, with another indelible foggy memory.

Fog fancier John Carey is a science correspondent for Business Week, based in Washington, D.C.

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