Agents of Erosion
You. Me. We all are.
When I was in college, my housemate and I, both geology majors, liked to call ourselves “Agents of Erosion.” We didn’t do anything to merit the sobriquet, we just thought it was funny, especially if you said it in an action-figure, smarmy kind of way. “AAAA-gents of EEE-ROWW-shunnnnn, shun, shun.” (Geology doesn’t have that many funny things about it so we took what we could.) I am not sure anyone would have agreed with us regarding our status, or our sense of humor, but I am used to that. To be frank, saying Agents of Erosion, even without trying to sound stupendous, still tickles me.
Erosional operatives, such as roots, salt, ice, and acid rain, are everywhere in the urban environment. Some might more correctly refer to them as weathering agents, as they merely weaken substrate such as concrete and asphalt and don’t ferret away the broken up bits, the mission of agents of erosion. Both forces are at work in Seattle, and every other town and city.
Winter is the season of reckoning with these nefarious urban forces of dilapidation and disintegration. When it snows, the city puts chains on bus tires, which is necessary for safety but also foments road abuse, the weakening and cracking of pavement. Cold weather also leads to the growth of potholes. Water has a rather unusual property of expanding when it freezes. (Only a handful of substances do, such as the ever popular antimony, gallium, and bismuth. When most liquids freeze, their molecules slow down, their bonds tighten, and they become more compact.)
The expansion of water translates to potholes, as water infiltrates pavement and turns to ice and cracks its surroundings. This may trouble vehicle drivers in the city but we need to get over ourselves because that ice expansion (about 9%) is a good thing for Earth. If water didn’t expand and float, I wouldn’t be here to write this and you wouldn’t be here to benefit from my scintillating prose because lakes would freeze from the bottom up, which would probably benefit no one, particularly anyone who wanted to live in a lake that didn’t became a solid block of ice. So next time you hit a pothole rejoice at the life affirming origin of the water/ice that formed it.
Less tied to life on earth but also problematic in the urban environment, salt is another frayer of the urban fabric. It is particularly troublesome in cities that salt their roads in winter though salt also arrives from the atmosphere and wave action. After it has infiltrated concrete or stone, salt crystals begin to grow and weaken the surrounding material. The sandstone in the video and images below illustrates how stone cannot withstand salt and ice weathering and how I actually am an Agent of Erosion.
I also have another more subtle effect in my ongoing role as an Agent of Erosion. And, not to forget all who read this, you, too, play the same role. All of us erode stone stairways, one microbit at a time, as our shoes strike and scrape the granite, limestone, sandstone, or travertine used for stairs. One place to see this in Seattle is Suzzallo Library on the UW campus, where decades of feet have created a slight indent in the travertine tread. The effect is far more pronounced in much older buildings, such as the Leaning Tower of Pisa, Westminster Abbey, and Angkor Wat.
We are not alone as living agents of erosion. Trees are notorious for the problems they cause with streets and sidewalks, which are no match for the forces roots impart. Ever expanding and spreading, roots buckle, deform, warp, disfigure, contort, and destroy the urban infrastructure. (Gotta love that thesaurus!) On some streets, I feel that I am on the surface of the sea as tree after tree thrusts up the sidewalk, creating regular waves of concrete that make walking difficult. I am not alone in realizing the challenges raised by roots. Over the past three years, people have filed 151 claims related to sidewalk falls against the City of Seattle and the city had spent $358,100 in settlements. Because of this issue, the city restricts what trees that can be grown along sidewalks, including bigleaf maple, cottonwood, and willows.
I still like to consider myself an Agent of Erosion though I know that I pale in comparison to the great agents affecting the urban environment. In contrast to me and my limited time spent wreaking havoc, they are always at work. As they say nature bats last, as well as first, second, and etc.
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