Archive | February 2022
February 23, 2022  

The Potomac River Floodplain

This post is going to talk about fluvial processes during the last few millennia, with the Potomac River as an example. A previous post discussed the geology of the Potomac’s fall line, where it drops out of the foothills of the ancestral Appalachian Mountains to the coastal plain before entering Chesapeake Bay. I’m going to keep this simple because, to be honest, fluvial geomorphology is not a straightforward topic. Rivers are constantly changing at time scales from years to millions of years. We won’t be walking back billions of years today, only a few hundred thousand, maybe a couple of million.

Figure 1. Schematic map, showing the location of the study area within northern Virginia (inset) and North America (double inset). Several features are labeled that will be referred to in the text and following figures. All photographs were taken within the black circled area. Note the labeled Holocene levee and Pleistocene terrace because they will be referred to later.

The lower Potomac River is braided, with multiple channels defining wooded islands (e.g. Van Deventer Island in Fig. 1). I won’t be talking about them but instead focus on what I saw, what the rocks (river sediment is unlithified rock to a geologist) tell me. The river flood plain extends to the Pleistocene terrace (yellow line in Fig. 1), which is about 80 feet higher in elevation than the river surface. No permanent structures have been constructed on the flood plain.

Some of the features we will examine are shown schematically in Figure 2. Note however, that the image shows a meandering stream whereas the Potomac is braided, which means that its channel doesn’t take those big loops shown in Fig. 2. That’s because the lower Potomac drops rapidly from Great Falls just upstream of the study area, to Washington D.C. in this area.

Figure 2. Schematic image of common river features.

We started out on the area labeled “Bluffs” in Fig. 2 and traversed the flood plain, following a tributary called Horsepen Run (see Fig. 1 for location). Note that Horsepen Run is a meandering stream, so we’ll see several features that scale downward from Fig. 2 as we cross the Potomac flood plain.

Figure 3. View looking downstream along Horsepen Run, showing fork in channel where debris collects during high flow. Note how shallow the flow is, the presence of large cobbles (some more than a foot in diameter), and erosion along the banks.

Horsepen Run (aka creek) drops quickly from the Pleistocene terrace (Fig. 1) but then crosses the Potomac flood plain and begins to meander. The photo in Fig. 3 is from a location just before this change in stream topography occurred.

Figure 4. View downstream of Fig. 3, showing coarse sediment inside of a meander forming a point bar.

The changes in stream morphology seen between Figs. 3 and 4 occur in larger streams (like the Potomac) but on much longer spatial scales.

Figure 5. Eroded bank of Horsepen Run, showing roots of a tree that cannot be more than a hundred years old. This indicates rapid downcutting and lateral movement of the channel. This kind of incision indicates a lowering of the stream’s base level, either due to uplift of the source or lowering of the receiving basin. For Horsepen Run, base level is where it enters the Potomac River (Fig. 6).
Figure 6. Confluence of Horsepen Run and Potomac River. The stream and river both have cut banks about 6 feet in height. There is no substantial delta at the mouth of Horsepen Run because of the coarseness of its sediment. Note the boulders seen in Figs. 3 and 4. This location is only a few miles from exposed Precambrian rocks.
Figure 7. View looking north, across the south fork of the Potomac River, towards Van Deventer Island which separates Virginia and Maryland. This is a rather large island in a terrain underlain by Precambrian rocks that are resistant to erosion. It is not a gravel bar as depicted in many representations of braided streams. Note the cut bank on the opposite shore, which is more than six feet in height (estimate only).

Figure 1 indicates the presence of natural levees (lower center of Fig. 1) near the main river channel. There is no “Yazoo Tributary” (see Fig. 2) at this location, so Horsepen Run cut across the Potomac’s natural levee. This can be seen beautifully in Fig. 8.

Figure 8. Meander in Horsepen Run cutting across the Potomac River’s natural levee, which is shown by the slope to the right side of the photo. The view is looking parallel to the Potomac’s channel at this location.
Figure 9. It is difficult to see the levee in this photo, which was taken from the top of the approximately 3-foot natural levee. Note the swale (low area) to the left side of the image. The levee isn’t as high as some (e.g., the Mississippi River) but it is quite noticeable, especially from ground level.

It was a beautiful February day to hike to across the Potomac River flood plain. I hadn’t expected to find so much dynamic geology so close to my new home, but there it was. The historic Potomac River transitions from its rocky confluence with the Shenandoah River at Harper’s Ferry, to the tidal river that defines Washington D.C., right here and, like America, it is not in equilibrium. The cut banks of the Potomac and its tributary, Horsepen Run, portend of rapid changes in the relative elevation of the land and the sea.

We are in for a wild ride…

February 21, 2022  

Review of “Gods and Beasts” by Denise Mina

Another random read, another crime drama, but this time an incomplete part of a series, starting nowhere and leading to a dead end, and best of all, based in Glasgow, Scotland. The dialogue may have been accurate but how am I to know? Even the narrator (the story is told in threads based on close-in POV characters) uses slang, which meant northing to me. I looked a lot of it up.

Grammar and punctuation followed the usual paradigm, deteriorating at the halfway point but, because of the slang used by the narrator I don’t know if it was intentional or not. This book should not have been released outside of Scotland, or maybe the U.K. Maybe it should have been translated to American English.

I am certain there is a plot, but it’s a lot bigger than this novel, which I was not told was incomplete when I started reading it. This piece of the story had no plot to speak of. It was like a narrative of a…actually it wasn’t even a good episode of a police drama. The solution of the crime graphically described on the back cover was only in the minds of the characters, with no actual evidence. Pretty cheap.

The cast of characters promised a lot but the plot (such as it was) failed to bring their stories together in anything close to a coherent picture. The author had a great idea but utterly failed to deliver an interesting and rewarding, not to mention entertaining, piece of imaginative fiction. This novel isn’t worth the time it takes to read the back cover.

Thank god I borrowed it from the library and didn’t waste my own money…

February 12, 2022  

Review of “A Consumer’s Republic” by Lizabeth Cohen

This is an older nonfiction book that has recently been rediscovered by the media. I heard an interview with the author on NPR and immediately purchased the Kindle version. Overall, I found it very entertaining and informative, despite a few issues. By the way, the subtitle is incorrect; the book is definitely not limited to “Postwar America,” assuming that is a reference to the Second World War. It actually starts at the turn of the twentieth century. It was first published in 2003, so it covers a tempestuous century of changes in how and why we buy stuff.

The grammar and punctuation are good, but the sentences get a little long, sometimes losing their train of thought and morphing into a new sentence before they end. I did a lot of rereading. At its core, this book is the culmination of an in-depth study of economic growth in New Jersey, extrapolated to the entire nation using reasonable assumptions, usually demonstrated to be legitimate. The Garden State is a good prototype because apparently that’s where the suburbs and mass marketing began, a response to the cost of living and lack of space in the New York City metropolitan area.

The author does a good job presenting the lighter side of consumerism while describing the struggle of disenfranchised groups (e.g., women and African Americans) to gain access to the market, which was seen as just as important as political rights. The entanglement of economic and political development is complex but presented pretty well in this book.

The author proves the existence of the “Consumer Republic” using many quotes from social leaders from the era that demonstrate the intentional development of the modern segmented, mass-market political economy called America. I had never heard any of this before, even though I lived through it and was one of the consumers that made it tick.

Everyone should at least be aware of their part in the evolution of identity politics in the segmentation of the mass market, which occurred over the last third of the twentieth century. It is a humorous and frightening story.

Unfortunately, I don’t think very many Americans will read this book (it is 800 pages long); at least, try to find a summary or, better yet, an interview with Lizabeth Cohen.

February 9, 2022  

Home World

“Excuse me sir, but could you tell me where I am?” 

The young man’s eyes were glazed when his stumbling progress stopped and he faced me. His countenance exploded in delight as he responded, “Oh, man, you are not from this world, it’s like I needed to meet an alien…”

“What?”

“I never met a blue man in person. Awesome!”

“Could you tell me where I am…on earth I mean?”

The young man wrapped his arm around my shoulder and said, “The more important question is where did you come from?”

I understood. He wouldn’t accept me without knowing my origins, as awkward as that might be. “I came here from another galaxy, a long way from here.” I realized that my ability to speak with this stranger, enabled by my universal translator, couldn’t bridge the gap in our life experiences.

The young man lit a cigarette and said, “Bring it on, dude!”

“What?”

“Tell me about your home planet. What’s it called?” 

I had to think a moment before responding. “Eclectic. I come from another galaxy, a planet where everyone does whatever they wish at any moment. Is that how it is here?”

The young man took a drag from his cigarette and said, “It can be pretty crazy, but I don’t know if it’s like Eclectic…I mean, that’s wild. Tell me more.”

“Let me see…on Eclectic people don’t have physical bodies so we don’t have houses to live in, or offices where we go to work, no freeways or metros—”

My companion stepped back and asked, “Are you like ghosts? Did you come from the afterlife? That is way cool!”

“Not at all. What I mean is that it isn’t like…this. I don’t have to walk to get around, so we don’t have roads or highways, no cars. We move between places by…hmmm…I just have to think about where I want to be.”

“I get it, like in Star Trek, with the transporter and all. Cool. What about trees and shit like that?”

“We don’t have any trees or plants on Eclectic. No wild animals either. What I mean is that life didn’t evolve like here, with bacteria and plants and animals and intelligence. We just skipped straight to the top of the evolutionary ladder, and became virtual beings, but grounded in reality–not ghosts…”

“Is Eclectic a planet, you know, like earth?”

“As far as our scientists can tell, we live in a subset of dimensions from the eleven that define the multiverse we share with you. There are no planets.”

“Do you have a family?”

“Yes. I have a partner and two children. We live in a beautiful sphere surrounded by a sea of blue methane, sparkling with effervescent bursts of red.”

“Why are you here?”

“I am an explorer.”

“So, you guys have like a NASA or some shit?”

I had been briefed on this universe, so I answered, “Yes, exactly the same.”He threw the cigarette into the street. “Cincinnati, Ohio.”