For billions of years Earth went fairly undisturbed in its natural, non-biological processes. First an active volcanic planet spewed out volcanic rocks, over time sedimentary rocks made their introduction along with the metamorphic. The Earth’s geologic creations determined the terrain of our lands, controlling erosion simply by the contrast of resistant and non-resistant formations. The introduction of life on Earth started affecting the land as early as the lower Ordovician, when small fauna started diversifying and digging through the sediments, disturbing the natural layers. Nothing, however, has changed the landscape of our planet more drastically than that of man. Once we had sedimentary, metamorphic and igneous as the only types of structures on the Earth. Today we have introduced an entirely new type of structure: The Urban rocks.
It doesn’t take a lot of imagination to start seeing a refined form of geology in the urban environment. Concrete is, after all, much like a sedementary rock. In the urban world, such as that which I experienced in my recent trip to Baltimore, MD and the Washington D.C. area, the laws of geology have been utterly ignored. In subway stations, the urban form of a cave, the “sedementary” rocks have been “deposited” long after the creation of the “cavern” itself. The law of original horizontality is largely ignored, and “igneous dikes” of granite intrude downwards into the earth rather than upwards from the mantle.
Often we imagine what the Earth will be like when we leave, wondering how long it will take nature to reclaim what was originally hers. We think of the trees and plants overtaking our buildings built of wood and can imagine it being reclaimed as early as 100 years from time of abandonment. But what about the concrete basements? The large blocks of limestone that have been transported from far away places to build castles and walls? These things, like rocks, have a geologic time scale of reclaiment. The streets, sidewalks, subways and buildings we have created out of our man-made rocks have created a new geology altogether. An urban geology.
What is most interesting about the interruption of the natural geology by the urban geology is the back and forth play. The interplay of natural forces and human created is constantly fluxing. As you travel through the D.C. metro, riding the escalators out of the subway, watch the concrete walls for the new deposits forming along the cracks. Like a cave, the subways of our urban environments are going through a dissolution process to create “speleothems” created by both nature and man. Take a look at a map of the Chesapeak bay: Inner Harbor is a place I love visiting with my cousin when I travel to Baltimore. The bay is much more geometrically constrained than allowed for in nature, contained by concrete blocks and dams that recreated the harbor that favored transport.
One of my favorite things to visit are old, abandoned buildings: namely warehouses and other commercial buildings made of brick, stone or other urban rocks. These buildings are remnants of the industrial revoloution, left to rot for half a century at this point in time, as the U.S. decided to start outsourcing a large percentage of our factory labor. The big concrete parking lots have turned into an urban sedementary unit, that has begun accumulating new deposits on top of it. Give these areas a couple thousand years and you will have natural sedementary units atop an urban sedementary unit. The urban geology even allows for more fractures and passage of water, perhaps an even more complex cave system can develop in the far future. Food for thought: What will metamorphosed concrete blocks look like?
Urban geology is something worth thinking about. It is a subject that has many faucets, and is growing in complexity every day. A combination of architecture, engineering and geology, this phenomenon is going to start growing more interesting every day as the natural cycles of the earth harmonize with the geology created by man.