jdp's blog

FLUVIOKARST CHRONOSEQUENCES

Historical contingency in fluviokarst landscape evolution was just published in Geomorphology 303: 41-52.  When I first came to central Kentucky in 2000 I began noticing the strong contrasts in landscape and landform development on inner vs. outer Kentucky River incised meander bends. Investigating this and related phenomena has occupied me off and on ever since. Only a few years ago I realized that given the nature of bend development over the past 1.5 Ma or so, the bend interiors represent a chronosequence of landforms. This paper exploits those chronosequences, using graph theory, to explore the role of historical contingency.

 

Chronosequence of strath terraces (T1, T2, T3) and other geomorphic surfaces at Polly’s Bend, Kentucky. The surfaces nearest the river are youngest; those farther away are oldest.

DOES RAINDROP SIZE MATTER?

Below is a picture of raindrop impact craters after a rain last month on a beach along the Neuse River estuary, N.C. The spot pictured has no overhanging trees or anything else, so the craters represent direct raindrop impacts. As you can see, assuming crater size is related to drop size, they represent a large range (the largest craters pictured are roughly 10 cm in diameter; the craters must be at least slightly larger than the drops). Rainsplash is a significant factor in soil erosion--even if not directly important, the process is key for dislodging grains or particles that are then transported by runoff. Drop impact also influences surface crusting and sealing, and thereby hydrological response. So, I got to thinking, what is the potential significance of such a large variation in drop size?

Kinetic energy is given by KE = 0.5 m V^2, where m is mass in kg, and V is velocity in m/sec. A 2 mm diameter raindrop has a mass of 4.19 mg and a terminal velocity of about 6.26 m/sec. This gives a kinetic energy of about  0.00008 joules per raindrop.

LOCAL ANOMALY OR CULTURAL SHIFT?

In my experience, beer cans and bottles discarded as litter in the kinds of places where I recreate and do field work are about 80 percent Bud Light, 17 percent other undrinkable watery American light beers, and 3 percent all other brands combined. Recently, however, at a site along the Neuse River, North Carolina, the two dozen or so trash bottles I saw  on the ground included NO Bud Lights!

I am not well versed enough in contemporary cultural or economic geography to speculate as to whether this is a local anomaly, a shift in taste preferences for the kind of sh*tbag Bud Light drinkers who trash the countryside, or an expansion of litterbug behavior beyond the Lite beer crowd.

Of course, when it comes to beverage container trash, no brand of beer, soda pop, or anything else comes close to the mass or volume of plastic water bottles. Why don't you people use canteens, reusable bottles, or at least recycle these things?

Posted 22 January 2018

 

BIRTH OF FERRICRETES

Ferricretes are soil or sediments cemented together by iron oxides. In eastern North Carolina, reducing conditions often prevail on the broad, flat interfluves. Under these conditions Fe is reduced, and soluble. Groundwater flow from these areas toward the major river valleys transports this dissolved ferric iron. When the groundwater discharges along the valley side slope it comes in contact with oxygen, and the iron oxidizes to its ferrous form. These iron oxides coat whatever material exists at that location--sand, clay, etc.

Limonite ferricrete at Fishers Landing, NC. The piece at the top is about 40 cm long. 

PATH EXTINCTION & REINFORCEMENT

The development and change over time (evolution) of geomorphic, soil, hydrological, and ecosystems (Earth surface systems; ESS) is often, perhaps mostly, characterized by multiple potential developmental trajectories. That is, rather than an inevitable monotonic progression toward a single stable state or climax or mature form, often there exist multiple stable states or potentially unstable outcomes, and multiple possible developmental pathways. Until late in the 20th century, basic tenets of geosciences, ecology, and pedology emphasized single-path, single-outcome conceptual models such as classical vegetation succession; development of mature, climax, or zonal soils; or attainment of steady-state or some other form of stable equilibrium. As evidence accumulated of ESS evolution with, e.g., nonequilibrium dynamics, alternative stable states, divergent evolution, and path dependency, the "headline" was the existence of > 2 potential pathways, contesting and contrasting with the single-path frameworks. Now it is appropriate to address the question of why the number of actually observed pathways is relatively small.The purpose of this post is to explore why some developmental sequences are rare vs. common; why some are non-recurring (path extinction), and some are reinforced.

THE GEOMORPHOLOGICAL NICHE OF TREES

In a 2009 article I introduced the concept of a geomorphological niche, defined as the resources available to drive or support a particular geomorphic process (the concept has not caught on). The niche is defined in terms of a landscape evolution space (LES), given by

where H is height above a base level, rho is the density of the geological parent material, g is the gravity constant, and A is surface area. The k’s are factors representing the inputs of solar energy and precipitation, and Pgrepresents the geomorphically significant proportion of biological productivity (see this for the  background and justification).

BREAKAGE VS. UPROOTING & HILLSLOPE GEOMORPHOLOGY

Just published in Geomorphology:

Samonil, P., Danek, P., Adam, D., Phillips, J.D. 2017. Breakage or uprooting: how tree death affects hillslope processes in old-growth temperate forestsGeomorphology 299: 276-284. 

The abstract is below:

Posted 14 November 2017

 

HOW COMPLEX CAN IT BE?

Back in 2006, novelist and country music singer-songwriter Kinky Friedman ran (unsuccessfully) for governor of Texas. His campaign slogan, a rather pointed reference to the fact that recent occupants of the office George W. Bush and Rick Perry were not the sharpest tools in the shed, was "how hard could it be?" I can't answer that, but I can answer, after a fashion, the question of how complex or simple an Earth surface system can be.

POWER LINES & FLOODPLAINS

As mentioned in my most recent post, in examining some of the imagery from recent floods in Texas, even in non-urban areas human infrastructure such as roads, levees, railways, and impoundments can profoundly influence flooding patterns and channel-floodplain hydrological and sediment connectivity. In several cases I noted that power line rights-of-way were zones of concentrated flow on the floodplain, which reminded me that I have seen similar phenomena elsewhere.

I am aware of work on the role of power lines in landscape ecology—as habitats, corridors, and as a factor in habitat fragmentation. I do not recall ever seeing anything about their role as channels or catch-basins for floodwater. The rights-of-way are typically vegetated, but often short, second-growth shrubs and grasses rather than the adjacent forests and trees. They may also be compacted enough to show slightly lower elevations than adjacent bottomland forests. In any case, they can clearly have strong local influences in channel-floodplain connectivity.

Pages

Subscribe to RSS - jdp's blog
X
Enter your linkblue username.
Enter your linkblue password.
Secure Login

This login is SSL protected

Loading