When more rain falls than the soil can absorb or plants can use, it has to go somewhere, and that movement is driven by gravity. Because concentrated flows are more efficient than sheet flows, concentrated and channelized flow paths are more likely to occur than diffuse flows. These pathways are also more likely to be reused, and to be enhanced by erosion associated with those flows. Similarly, when two of these threads of flow meet, they typically combine (less total surface area for the same amount of water = greater efficiency). Thus these channelized flows tend to form branching channel networks.

The formation of stream and river channels and networks is thus an emergent property of efficiency selection--those most efficient flow paths are more likely to arise in the first place and to be preserved and enhanced. The fact that most of these systems eventually lead to the sea (though globally, a surprisingly large minority drain to interior continental basins) is due to the fact that the flows are gravity driven, and for water, the ocean is the low point.


Just published in Earth-Science Reviews, and available via:

I'm happy to have my name on this, and contributed enough to justfiy that, but this was not an equal contribution by all authors--Lukasz gets most of the credit!



I've just spent a couple of excellent weeks working on a project investigating biogeomorphic impacts of trees, particularly in old-growth forests. With Pavel Samonil (Forest Ecology Dept., Sylva Tarouc Inst., Brno) and his PhD student Pavel Danek, we visited a number of sites in the Czech Republic. There is much to be done--some of the impacts we identified have never been studied before; others have been studied enough to reveal some complex questions and uncertainties. A sampling of what we saw follows.









I’ve been working on and off on scale linkage problems for more than 30 years. The most recent effort, Vanishing Point: Scale Independence in Geomorphological Hierarchies, has just been published.

The abstract is below:


There are four main mechanisms of bedrock channel erosion—abrasion, dissolution, cavitation, and weathering-and-plucking. The latter occurs when weathering along joints and bedding planes of the bedrock loosens slabs or clasts, which are then entrained (plucked) during high flows. Cavitation is difficult to observe or prove in the field, but likely occurs in the stream I visited this week, Raven Run (near Lexington, KY). The other mechanisms all clearly exist.

Weathering and plucking is the dominant erosion mechanism of the bedrock streams hereabouts—the photo shows the flat surfaces and angular features that result from weathering along the horizontal bedding planes of the limestone and the frequent vertical joints, and subsequent removal of the resulting slabs.

Raven Run, Kentucky.


Gonzo Geomorphology

I recently gave a talk at EGU called Vanishing Point: A Savage Journey to the Heart of the Scale Hierarchy (abstract here). The title is borrowed/inspired from the iconic 1971 movie Vanishing Point (director: Richard Sarafian) and the subtitle to Hunter S. Thompson’s 1971 Fear and Loathing in Las Vegas—A Savage Journey to the Heart of the American Dream.

The “vanishing point” terminology refers to methods to determine how far apart elements of a scale hierarchy have to be before they are no longer directly related. I attempted to justify the “savage journey” with the argument that the scale domain, as opposed to the spatial and temporal domain, is little explored and largely unknown.

Hunter S. Thompson, by Ralph Steadman (an illustrator who worked with HST;

Jennifer Hyndman - Refugees on the Edge: 'Distant Suffering' or Domesticated Distance?



Part of the 44th Annual Ellen Churchill Semple Day

Aprill 22, 2016 Department of Geography College of Arts & Sciences University of Kentucky



Rich Donohue: "Finding the Plus in New Maps Plus"

Mrach 25, 2016 - 3:30pm 234 Classroom Building Rich Donohue, Postdoctoral Researcher in the Department of Geography at the University of Kentucky

Geomorphological Flickering

Geomorphological Flickering

As environmental systems approach critical thresholds or tipping points, they may experience increased variability, which in the literature on critical environmental state transitions has been referred to as “flickering” (e.g., Lenton, 2011; Scheffer et al., 2012; Dakos et al., 2013). This is primarily the case for noisy, stochastic systems, which is not the case for many lab and mathematical models, but is emphatically so for most real-world environmental systems. As Dakos et al. (2013) put it:

Most work on generic early warning signals for critical transitions focuses on indicators of the phenomenon of critical slowing down that precedes a range of catastrophic bifurcation points. However, in highly stochastic environments, systems will tend to shift to alternative basins of attraction already far from such bifurcation points. In fact, strong perturbations (noise) may cause the system to “flicker” between the basins of attraction of the system’s alternative states. As a result, under such noisy conditions, critical slowing down is not relevant, and one would expect its related generic leading indicators to fail, signaling an impending transition.

Dispatches From Vienna

Some miscellaneous observations from the 2016 General Assembly of the European Geosciences Union in Vienna . . . .

Major Concepts = Excellent Session

I participated in a paper session called “Beyond the Case Study: Concepts in Earth Sciences.” Geosciences are of course built on case studies, and without them we would have no useful or interesting theories, hypotheses, syntheses, or conceptual frameworks. But in a professional meeting context you get a bit tired of sitting through the detailed results from yet another watershed monitoring study, lab experiment, numerical model, paleoenvironmental reconstruction or what have you. Unless these things are dead on your own interests, it is much more interesting to be challenged by some big ideas and overarching concepts and themes.

That’s what this session was all about, and it went well. It is rare—in fact I can’t remember the last time—I sat through six presentations in a row that all held my full attention from start to finish.


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