Architectural-Element Analysis: A New Method of Facies Analysis Applied to Fluvial Deposits

Data drawn from a global compilation of studies quantitatively confirm the long-articulated contention that erosion rates from conventionally plowed agricultural fields average 1–2 orders of magnitude greater than rates of soil production, erosion under native vegetation, and long-term geological erosion. The general equivalence of the latter indicates that, considered globally, hillslope soil production and erosion evolve to balance geologic and climate forcing, whereas conventional plow-based agriculture increases erosion rates enough to prove unsustainable. In contrast to how net soil erosion rates in conventionally plowed fields (≈1 mm/yr) can erode through a typical hillslope soil profile over time scales comparable to the longevity of major civilizations, no-till agriculture produces erosion rates much closer to soil production rates and therefore could provide a foundation for sustainable agriculture.

https://www.pnas.org/content/pnas/104/33/13268.full.pdf

Soil erosion and agricultural sustainability

応用水文 = Applied hydrology

This article serves as an introduction to the papers dealing with braided river deposits in this volume. A lithofacies code erected earlier by the writer is expanded to include matrix-supported gravel, low-angle cross stratified sand, erosion surfaces with intraclast conglomerates, and massive mud deposits. The four vertical profile models erected by the writer are expanded to six. A new model, the “Trollheim type” is proposed, to include gravelly deposits characterized by abundant debris flows. The Donjek sequence type is restricted to gravel-dominated cyclic deposits and a new model, the “South Saskatchewan type”, is erected for sand dominated cyclic deposits. The Scott, Platte and Bijou Creek models remain essentially unchanged.

Lithofacies Types and Vertical Profile Models in Braided River Deposits: A Summary

Foreword 1. Introduction 2. Runoff, erosion and delivery to the coastal ocean 3. Temporal variations 4. Human impacts Appendices. Global River Database: Appendix A: North and Central America Appendix B: South America Appendix C: Europe Appendix D: Africa Appendix E: Eurasia Appendix F: Asia Appendix G: Oceania References Index.

/pdf/river-discharge-to-the-coastal-ocean-a-global-synthesis-571z1g19ts.pdf

River Discharge to the Coastal Ocean: A Global Synthesis

The human population has been increasing exponentially. Simultaneously, as digging sticks and antlers have given way to wooden plows, iron spades, steam shovels, and today’s huge excavators, our ability and motivation to modify the landscape by moving earth in construction and mining activities have also increased dramatically. As a consequence, we have now become arguably the premier geomorphic agent sculpting the landscape, and the rate at which we are moving earth is increasing exponentially. As hunter-gatherer cultures were replaced by agrarian societies to feed this expanding population, erosion from agricultural fields also, until recently, increased steadily. This constitutes an unintended additional human impact on the landscape.

/pdf/on-the-history-of-humans-as-geomorphic-agents-1agq8nx5hi.pdf

On the history of humans as geomorphic agents

Alluvial fans were studied in the field, largely in the desert regions of California, and in the laboratory. Field study consisted of detailed mapping of parts of four fans and reconnaissance work on over one hundred additional fans. Features mapped included the nature and age of deposits, material size, and channel pattern. In the laboratory small alluvial fans were built of mud and sand transported through a channel into a 5-foot by 5-foot box under controlled conditions. Material is transported to fans by debris flows or water flows that follow a main channel. This channel is generally incised at the fanhead, because there water is able to transport on a lower slope the material deposited earlier by debris flows. The main channel emerges onto the surface near a midfan point, herein called the "intersection point." On laboratory fans most deposition above the intersection point is by debris flows that exceed the depth of the incised channel. Fluvial deposition dominates below the intersection point. This depositional relation probably also occurs on natural fans. On fans deficient in fine material large discharges may infiltrate completely before reaching the toe of the fan. Coarse debris is then deposited as lobate masses, herein called "sieve deposits." In many respects sieve deposits resemble debris-flow deposits, but they lack primary fine material, and fresh lobes are highly permeable.

Processes on arid-region alluvial fans1

Why study glaciers? some basic concepts mass balance flow of a crystalline material the velocity field in a glacier temperature distribution in polar ice sheets the coupling between a glacier and its bed water flow in and under glaciers - geomorphic implications stress and deformation stress and velocity distribution in an idealized glacier applications of stress and deformation principles to classical problems response of glaciers to changes in mass balance problems

Principles of glacier mechanics

Subhourly measurements of bed deformation, bed shear strength, subglacial water pressure, and surface speed at Storglaciaren, a glacier in northern Sweden, showed that the shear-strain rates of the bed decrease during periods of high water pressure and surface speed. High water pressures appear to be accompanied by a reduction in the coupling of ice with the bed that is sufficient to reduce or eliminate shearing. The instability of large ice masses may result from similar decoupling rather than from pervasive bed deformation, as has been commonly thought.

https://science.sciencemag.org/content/sci/267/5194/80.full.pdf

Flow mechanism of glaciers on soft beds.

In a 1-m wide, meandering flume with movable sand bed, uniform flow was established at discharges of 20, 35, and 50 1/sec. Bed shear stresses, bed geometry, the distribution of sediment in transport, and the strength of secondary flow were determined at each discharge. The zones of maximum bed shear stress, \tau, and maximum sediment discharge per unit width, $$q_{s}'$$, coincide. They are on the point bar in the upstream part of the bend, cross the channel centerline in the middle or downstream part of the bend, and follow the concave or down-valley bank to the next point bar downstream. With increasing discharge, secondary currents increase in strength. Consequently, the zone of maximum \tau and $$q_{s}$$ remains closer to the inside bank across the point bar, and crosses the channel centerline somewhat lower in the bend. It appears that bed geometry is adjusted to provide, at each point on the bed, precisely the shear stress necessary to transport the sediment load supplied. For example, the gradual de...

Roger LeB. Hooke

Papers

On the history of humans as geomorphic agents

Processes on arid-region alluvial fans1

Principles of glacier mechanics

Flow mechanism of glaciers on soft beds.

Distribution of Sediment Transport and Shear Stress in a Meander Bend