D e s e r t E x p o s u r e
April
2008
Seeing Things
Chasing the elusive "superior mirage."
Story and photos by Nancy Gordon
Have you ever driven through a New Mexico desert when mystery shrouds the mountains? The landscape becomes unpredictable. Peaks turn into mushroom caps. Capricious castles appear and disappear. Cliffs rise from the desert and spread across an invisible ceiling.
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Superior mirages make the mountains appear to have sprouted ears. |
You blink and look again. Now the edge of a mesa is being erased by an invisible hand. Trailing wisps of cloud-mountains linger, then let go. Suddenly the scene shifts back to normal, and you wonder what just happened.
These are mirages, Nature's sleight of hand. Now you see them, now you don't. More specifically, the mutable mountains are a type of superior mirage, as opposed to the more familiar inferior mirages that produce illusions of water on the highway or shimmering lakes in the desert. The terms "superior" and "inferior" have to do with the location of a mirage and not its beauty — although when I once told an artist that the shape-shifting foothills she'd seen were superior mirages, she replied, "They certainly are!"
Both types of mirages are due to refraction of light. A familiar example of refraction is the way a pencil "bends" when it is placed slantwise into a glass of water. Light rays travel more slowly through water than through air.
In the atmosphere, refraction occurs when light passes through air of different densities. The bending of light is more pronounced where densities abruptly change, as at the boundary between cold and warm layers of air. Light rays always bend towards the denser (colder) air.
The "water on the highway" mirage occurs when the asphalt heats up and a warm layer of air forms just above it. Light rays passing near the asphalt are bent upwards towards the cooler air above. The "water" is actually light rays from the blue sky being refracted upwards towards our eyes. It is below the real sky (inferior to it).
In contrast, the desert mountain mirages require a strong inversion layer of colder air near the ground, with warmer air above. The top of the inversion layer acts somewhat like a mirror suspended overhead. Light rays are bent downwards towards our eyes. The mirages we see are the mirrored, distorted images of mountains and sky layered on top of-superior to-the real ones.
For a strong inversion layer to form, the air must be still. Any wind, any turbulence, will cause the "mirror" to break. It is best to look for mirages early in the day, because the inversion layer will dissipate as the earth warms (although mirages can sometimes also be seen at dusk). To see the mirages, your eyes must be near the top of the inversion layer. As you drive towards the mountains, rising and falling with the road, the mirages constantly change, arising and fading and reappearing in more distant mountains or even behind you.
Superior mirages can also occur when a cold layer of air forms over expanses of ice or water. In the book Sea of Cortez, John Steinbeck wrote about the mirages over the Gulf of California that made distant islands visible, distorted the land, and produced a "heady, crazy feeling in the observer." They inspired thoughts of dreams, miracles and fairy tales of invisible kingdoms.
Others have long associated mirages with the mystical. A complex type of superior mirage in which several layers of stretched, compressed, inverted or upright images are stacked together is called the Fata Morgana. The name is Italian for Morgan le Fay, the legendary half-sister of King Arthur who lived in a crystal palace under the sea and could create castles out of thin air. Italian poets gave the name to the fantastic, castle-like mirages that occur commonly over the Strait of Messina.
It was on a clear, calm morning several years ago, while traveling on Hwy. 180 from Silver City to Deming, that my husband and I first noticed the mirages casting their spell over the Floridas and Tres Hermanas mountain ranges. I saw the mirages again several times on casual trips southward. It seemed easy enough to encounter them without trying — but when I set out to capture them with my camera, they proved elusive.
I gave it a try one cold April morning, leaving Silver City before dawn. When I rounded the tailings piles south of Hurley, I could see the lights of Deming unnaturally bright in the distance, and as I got closer, the headlights of cars on Interstate 10 radiated vertical bands like lighted towers. Yes, I thought, it was a good day for mirages.
But by the time the sun broke over the horizon, a breeze was already stirring. I was granted only a fleeting vision of false flat-topped hills that quickly winked out. Turning around, I drove back and then forward again over the same stretch of road, trying to will the mirages into existence. A sense of desperation and longing consumed me, and I had to keep reminding myself to watch for traffic. Finally, I headed home, feeling confused and disappointed. What had I done wrong?
Maybe I needed a more scientific approach. I read up on superior mirages, and found that they were more likely to occur on cold mornings after a clear, dry night, when previous days had been warm with little wind. By the time cold weather returned the following winter, I felt better prepared to pursue mirages. This time, I diligently studied weather forecasts on television and at NOAA's website (www.srh.weather.gov), and picked days when conditions looked good: morning temperatures of 20s rising to the 50s at noon, no wind, no clouds.
Twice again I was foiled. Mirages, I concluded, did not like to be chased.
Then, one morning in early January of this year, I was up early and noticed the lights in Silver City twinkling in a stuttering sort of way. Even though the weather conditions weren't mirage-friendly, something told me to grab my camera and go. As I approached the flatlands on the way to Deming, it was about 7:30 a.m. and the sun was barely up. I was paying more attention to the surprisingly heavy commuter traffic than to my surroundings when, suddenly, there they were!
Out of the corner of my eye, I could see grasslands and creosote stretching into vertical cliffs and the mountains beginning to dissolve. I stopped at several points to take photos. The mirages always looked smaller and less dramatic when I got out of the car, and were nothing like the ones that loomed large in my memory. Nevertheless, they registered on my camera under maximum zoom.
I sat for a while just watching the mirages, mesmerized. "Ears" sprouted from mountainsides. A bubble separated from a summit and evaporated. I was swept into the shifting landscape. It was real but unreal. The physics of atmospheric optics and refraction didn't explain why I felt at peace, complete.
By 8:15 a.m., a breeze was rustling the creosote bushes. Gradually, the landscape settled back into its normal contours. With a sigh, I started up the car and pulled onto the highway. I had been in the presence of the supernatural, and the return trip seemed flat.
To learn more about superior mirages, try these Web sites:
www.weatherscapes.com
www.islandnet.com/~see/weather/elements/mirage1.htm or mintaka.sdsu.edu/GF/mirages/mirintro.html
Nancy Gordon is a former hydrologist who lives in Silver City.