geology

DYNAMIC EQUILIBRIUM (?) IN RIVERS

Nicholas Pinter, a Southern Illinois University geomorphologist, gave a nice talk yesterday on rivers and flooding in the 21st century as part of UK’s Water Week. Pinter’s talk got me to thinking about the concept of “equilibrium” in environmental systems and what it means to both geoscientists and laypersons. Pinter correctly noted that rivers tend toward dynamic equilibrium, and more specifically, dynamic metastable equilibrium. This means three things: First, the system (river) is more or less constantly changing (the dynamic part). Second, equilibrium is of the type envisioned in mathematics and systems theory—that is, a state or condition the system settles into after a change or perturbation, with no further connotation other than that the response to the change has run its course (I’ve called this “relaxation time equilibrium” in my work). Third, “metastable” means that these equilibrium states are not necessarily stable and self-maintaining, and may be sensitive to future disturbances—even relatively small ones. Pinter’s message is that dynamic equilibrium in rivers means that rivers are constantly changing.

THE TRIAD

Explaining and understanding Earth surface systems almost always requires some triangulation between three different sets of factors. The first, examples of which are shown on the lower left corner of the triangle below, are general principles and relationships that apply everywhere and always. Second, on the upper point, are environmental factors--characteristics of locations and regions such as climate, geology, etc. On the lower right of the triangle is the third set of factors, related to past events and time available for the system to develop.

This can be generalized as laws, place, and history, as shown below. 

BADASS GEOMORPHOLOGY

Yesterday I was honored to give the annual Linton Award lecture to the British Society for Geomorphology at the University of Manchester. Many thanks to the BSG for making my attendance possible, and to the U. Manchester geography department for putting on a good meeting. This is the abstract of my talk, entitled Badass Geomorphology:

Chellgren Center Honors 43 New Fellows

OCBILs & YODFELs

 

I recently stumbled upon the OCBIL theory. In the words of Hopper (2009): “OCBIL theory aims to develop an integrated series of hypotheses explaining the evolution and ecology of, and best conservation practices for, biota on very old, climatically buffered, infertile landscapes (OCBILs). Conventional theory for ecology and evolu- tionary and conservation biology has developed primarily from data on species and communities from young, often disturbed, fertile landscapes (YODFELs), mainly in the Northern Hemisphere.” As a geomorphologist, and in particular a biogeomorphologist interested in coevolution of landscapes, biota, and soils, the OCBIL-YODFEL contrast is extremely interesting—mainly because it implies a key role for landscape age, stability, and geomorphic disturbance regimes in the development of ecosystems and evolution of biodiversity patterns.

PHYTOTARIA, SOILS, & LANDFORMS

 

One of my major research interests is the coevolution of soils, landforms, and biota. I’ve been working in this area pretty steadily since about 2000, but until 2013 I was completely unaware of some work being done along the same lines, over about the same time period. This is the work of W.H. Verboom and J.S. Pate from Western Australia, who among other things developed the “phytotarium concept.” Phytotarium defines the specific plants and microbial associates driving specific pedological changes during niche construction. This concept, and a wealth of work on biogenic origins of pedological and geomorphological features such as clay pavements, texture-contrast (duplex, as they call them in Australia) soils, and laterites, was highly relevant to my own thinking (e.g., Phillips, 2009a; 2009b), but though I consider myself familiar with the biogeomorphology and pedogenesis literature, then and now, I had somehow missed it.

Deep sandy duplex (vertical texture contrast) soils, Western Australia. Photo credit: Dept. of Agriculture & Food, Western Australia.

Sycamores and Hillslopes

Below are some recent photographs of sycamore trees (Platanus occidentalis) in limestone bedrock at Herrington Lake, Kentucky (about37.78o N, 84.71o W). As you can see, the tree roots and trunks exploit joints in the rock, and accelerate weathering both by physically displacing limestone slabs and widening joints by root growth, and by facilitating biochemical weathering along both live and dead roots.

Sycamores rock

These are some nice examples of root/bedrock interaction, and the general phenomena are not uncommon, though usually much more difficult to see. The Herrington Lake shores also appear to illustrate a process by which the sycamores accelerate weathering and mass movements (other trees are also involved, but Platanus occidentalis seems to be the most common and effective):

1. Plants colonize the exposed bedrock, with roots exploiting bedrock joints.

2. Tree roots accelerate weathering and loosen joint blocks.

3. While the tree is still alive, root growth envelopes rock fragments and the trees provide a physical barrier to downslope transport.

Geomiracles

 

Science fiction and popular science writer Arthur C. Clarke once wrote that "any sufficiently advanced technology is indistinguishable from magic." Riffing on that theme, I once gave a talk in which I proclaimed that "any sufficiently improbable event is distinguishable from the miraculous." Some definitions of "miracle" invoke the divine or supernatural, but I have in mind the definition (in this case from the Merriam-Webster dictionary) as: "an extremely outstanding or unusual event, thing, or accomplishment." The point of the argument is that, due to the inescapable, irreducible role of geographical and historical contingency in Earth surface systems, all such systems (landscapes, ecosystems, soils, etc.) are unique in some respects (a formal argument along these lines is presented in this article: Phillips, J.D.  2007.  The perfect landscape.  Geomorphology 84: 159-169.). Thus the probability of existence of any given state of any given system at a given point in time is infinitesimally low. This exceedingly low probability makes nearly any environment in some senses extremely outstanding and unusual, and thus a miracle.

When The Levee Breaks: Derek Sawyer's Research Goes To Great Depths

For most Americans, levees are man-made engineering projects, rarely mentioned outside of the flooding that follows disasters like Hurricane Katrina.However, recent research conducted by Earth and Environmental Science (EES) Assistant Professor Derek Sawyer published in the journal “Geology” sheds new light on levees most of us never see – those built naturally by underwater rivers deep below the ocean’s surface.

KGS Research Examines New Madrid Fault Seismic Zone

In a recent publication in the journal Science, the Kentucky Geological Survey examines seismic activity in the New Madrid Seismic Zone.

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