Rock Talk By Larry Larason

Dust
Blowin' in the Wind

Dust is a poetic metaphor for death and decay, the bane of fastidious housekeepers, and an irritant to our sinuses. But we seldom think of dust geologically. Obviously, dust storms are a form of erosion – soil is moved from one place to another. For example, the Great Sage Plain in the Four Corners lies between Bluff and Monticello, Utah, extending into Colorado. It had been eroded down to Dakota Sandstone bedrock before winds deposited a layer of soil as much as 20 feet thick on it. Geologists call windblown soil "loess." That's pronounced "luss." Around the world loess is found in thick deposits. In Illinois and Iowa the loess is as much as 200 feet thick. In parts of China it is may be 300 to 1000 feet deep. Much of it originated as "rock flour" ground down by continental glaciers during the last ice age. During dry seasons it was whipped up by winds and dropped on surrounding regions.

I started thinking about dust last May [2006] when we had a day with gale force winds and lots of dust and grit in the air. I was reminded of a field trip I led to the Great Falls of the Little Colorado on a day like that, and one of the participants was nearly blown off the edge of the gorge.

Earth isn't the only planet with dust storms. Last May was also about when news came out that Titan, a moon of Saturn, had "sand dunes"; of course, the "sand" on Titan is composed of water ice or frozen carbon compounds, rather than silica, as on Earth. It may be small consolation that dust storms on Mars are worse -- they can cover the entire planet and may last for months. The monsoon rains put dust out of my mind for awhile, but then as I wrote part of this on September 20th, high wind in advance of a storm front raised dust west of town again, although by mid-afternoon we had rain.

That day last May was miserable, but I've seen worse. My home town in western Oklahoma was on the margin of what had been the Dust Bowl in the 1930s. When I was in high school we had a few of those storms like the ones during the Dust Bowl days, when a wall of black dirt came roaring over town obscuring the sun. I found them fascinating, but now that I'm older I wonder what went through the minds of the adults in my home town, most of whom had survived the Dust Bowl. Did they fear that such storms heralded another decade of despair on the Great Plains?

When I lived in Phoenix there were a few storms like that, too. But in Phoenix the dust was raised by downbursts from thunderheads and was followed soon by torrential rain. Such events are awe inspiring, but I'd rather not experience one again.

And I've seen worse in Gallup, as well. Remember April, 2001? As I recall the wind was slight on the morning of the twelfth, but we awoke to a pall over the sky. It was so bad that park rangers across the West were being asked where the forest fires were. What was unusual that day was that the dust came from the Gobi desert, nearly half-way around the world. The jet stream brought a repeat performance of that Asian haze during the same month that year. That's when we learned that China has its own dust bowl now, brought about, in part, by many of the same abuses of the land that caused America's problems. The Gobi desert may be the worst source of dust, but just south of it is the Ordos Desert, and to the west is the Taklamakan Desert. Spring winds crossing these areas, as well as abandoned or overgrazed farmlands, inundate eastern China with dust and often carry it on to Korea and Japan. It has been estimated that 300,000 Chinese die prematurely each year because of respiratory distress brought on by the dust. And part of that dust comes from China's nuclear test site, so it may include radioactive particles. Beijing is set to host the summer Olympics in 2008, but athletes won't want to compete where they might damage their lungs. China undertook a project beginning in 1978 that may ameliorate the situation: they are building a new "great wall". This wall will consist of trees and grasses planted along the border with Mongolia. It is hoped that the trees will provide a wind break to reduce the dust blowing toward Beijing, Korea, Japan…and us.

So China's problem is our problem, as well. It's a single example of how we all share one planet. Another example is seen on the Caribbean islands and east coast, where dust blowing off the Sahara Desert in northern Africa often comes to rest. One benefit to the region is that iron and phosphorus are added to the soil; this is especially important in Brazil's rain forests. However, when a plume of African dust flies over, people experience more asthma attacks. An even more sinister aspect is that the dust contains spores and viruses. Most Southwesterners have heard of coccidioidomycosis, better known as "Valley Fever", a debilitating and occasionally fatal fungal infection that is contracted when spores are lofted in dust by wind in dry parts of our region. Well, researchers in the Virgin Islands have found 110 varieties of spores and bacteria in the African dust. One of them, aspergillus, is blamed for killing coral in the Caribbean. Another blights sugarcane and is believed to have come from Cameroon, where it is endemic.

In October 2006 a study was published showing that African dust storms have a negative correlation with hurricanes. That is, as more dust blows off the Sahara fewer hurricanes occur, although it's not yet clear why this is so. Survivors of Katrina might see this as a beneficial trade-off, despite the chance of infections.

Recent research near Telluride and Silverton brought to light some bad news about dust and mountain snow packs. Much of the West depends on snow runoff for irrigation and even drinking water. During droughts more dust blows in the air and falls on snow fields in the mountains. Scientists have been worried about global warming spurring faster melting, but, surprisingly, dust hastens the melting of snow faster than higher atmospheric temperatures, because the dust absorbs heat from sunlight. And, when spring runoffs occur earlier, it makes summers drier..., which results in more dust. It is a self reinforcing cycle.

Dust is inescapable. So how much dust are we talking about? Dust doesn't weigh much, right? Well, one scientist has estimated that three billion tons of it moves around the world each year. That's a lot of dust! And then there is meteoric, or inter-planetary, dust. But that's another story.