Toe-cut terraces Larson, Phillip H; Dorn, Ronald I; Faulkner, Douglas J ...
Progress in physical geography,
08/2015, Letnik:
39, Številka:
4
Journal Article
Recenzirano
Alluvial fans and fluvial terraces occur in nearly all climatic settings and often coexist within the same drainage basin. These landforms play an important role in understanding the geomorphic, ...hydrologic, sedimentologic and erosional histories of a basin. The juxtaposition of fans and fluvial terraces, in some instances, can lead to misinterpretation in distinguishing traditional fluvial terraces from the truncated toe of tributary alluvial fans. This becomes particularly troublesome for those attempting to interpret results from published field studies where fan-cut terrace, truncated alluvial fan, toe-cut alluvial fan, alluvial terrace, and incision of the lower end of a fan piedmont all refer to the same genetic landform. We call for use of the term "toe-cut terrace" to represent this landform. We also present criteria to aid in the identification of toe-cut terraces, defined as an abandoned alluvial surface, formed by the truncation of the distal portion of tributary alluvial fans by streams flowing obliquely or perpendicular to the fan surface. Truncation occurs through lateral erosion ("toe-cutting") or through vertical incision by the trunk drainage lowering the base-level of the alluvial fan. This results in incision into the fan surface abandoning the fan's depositional surface at a higher level above the modern floodplain - a form that often resembles a fluvial terrace. A case study from the Sonoran Desert in central Arizona illustrates a sequence of abandoned alluvial surfaces that resemble fluvial terraces, but use of the proposed criteria reveal the presence of both toe-cut terraces and traditional fluvial terraces formed by the abandonment of the rivers former floodplain.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, ODKLJ, OILJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Mountains cover a quarter of the Earth’s land surface and a quarter of the global population lives in or adjacent to these areas. The global importance of mountains is recognized particularly because ...they provide critical resources, such as water, food and wood; contain high levels of biological and cultural diversity; and are often places for tourism and recreation and/or of sacred significance. This major revision of Larry Price’s book Mountains and Man (1981) is both timely and highly appropriate. The past three decades have been a period of remarkable progress in our understanding of mountains from an academic point of view. Of even greater importance is that society at large now realizes that mountains and the people who reside in them are not isolated from the mainstream of world affairs, but are vital if we are to achieve an environmentally sustainable future. Mountain Geography is a comprehensive resource that gives readers an in-depth understanding of the geographical processes occurring in the world’s mountains and the overall impact of these regions on culture and society as a whole. The volume begins with an introduction to how mountains are defined, followed by a comprehensive treatment of their physical geography: origins, climatology, snow and ice, landforms and geomorphic processes, soils, vegetation, and wildlife. The concluding chapters provide an introduction to the human geography of mountains: attitudes toward mountains, people living in mountain regions and their livelihoods and interactions within dynamic environments, the diverse types of mountain agriculture, and the challenges of sustainable mountain development.
The objective of this study was to document newly qualified veterinarians' concerns and surgical complications encountered during canine ovariohysterectomy (cOVH) during the first year of general ...practice. A questionnaire investigating concerns about cOVH procedures was sent to all final-year veterinary students (group 1) enrolled at five UK universities. Participants were later asked to complete a similar questionnaire 6 months (group 2) and 12 months (group 3) after graduation, which involved grading their concern about different aspects of the cOVH procedure and reporting surgical complications encountered after completing three cOVHs. Responses were compared between different time points. There were 196 respondents in group 1, 55 in group 2, and 36 in group 3. Between groups 1 and 2, there was a statistically significant reduction in the respondents' levels of concern in every aspect of cOVH (p<.05). Between groups 2 and 3, there was no statistically significant change in respondents' levels of concern in any aspect of cOVH (p≥.21). There was a significant reduction in the number of complications encountered by veterinarians in group 3 (39/102, 38.2%) compared to those in group 2 (117/206, 56.8%) (p=.002). Employers should anticipate high levels of concern regarding all aspects of cOVHs in new graduates, and supervision during the first 6 months may be particularly useful.
Mountain Geography Martin F. Price, Alton C. Byers, Donald A. Friend, Thomas Kohler, Larry W. Price / Martin F. Price, Alton C. Byers, Donald A. Friend, Thomas Kohler, Larry W. Price
2013
eBook
Mountains cover a quarter of the Earth's land surface and a quarter of the global population lives in or adjacent to these areas. The global importance of mountains is recognized particularly because ...they provide critical resources, such as water, food and wood; contain high levels of biological and cultural diversity; and are often places for tourism and recreation and/or of sacred significance.This major revision of Larry Price's book Mountains and Man (1981) is both timely and highly appropriate. The past three decades have been a period of remarkable progress in our understanding of mountains from an academic point of view. Of even greater importance is that society at large now realizes that mountains and the people who reside in them are not isolated from the mainstream of world affairs, but are vital if we are to achieve an environmentally sustainable future. Mountain Geography is a comprehensive resource that gives readers an in-depth understanding of the geographical processes occurring in the world's mountains and the overall impact of these regions on culture and society as a whole. The volume begins with an introduction to how mountains are defined, followed by a comprehensive treatment of their physical geography: origins, climatology, snow and ice, landforms and geomorphic processes, soils, vegetation, and wildlife. The concluding chapters provide an introduction to the human geography of mountains: attitudes toward mountains, people living in mountain regions and their livelihoods and interactions within dynamic environments, the diverse types of mountain agriculture, and the challenges of sustainable mountain development.
Rhyolite domes formed over a million year continuum in eastern California are used to study boulder dominated slopes. Slopes in this study are steep （-25°to-35°） and are made of coarse boulder sized ...blocks. These slopes include well varnished vertically oriented colluvial deposits that have been likened to relict periglacial stone stripes, or as indicated in this study, are the result of ongoing desert slope processes. The deposits are common throughout the arid southwestern US, but their morphometric character, fabric, and rates of formation have not been assessed systematically. Results indicate that boulder deposits examined here are remnant from the original surface formed during volcanic eruption and that these boulder slope deposits evolve slowly. Grain size, grain shape and grain angularity do not change significantly from genesis to -0.6 Ma; trends in the data change markedly after that time. Mean eigenvectors indicate a fabric oriented downhill, parallel to the slope, consistent with the visual impression that long thin to plate-like rocks orient themselves similarly; however, fabric is actually randomly dispersed, similar to that at slope genesis, as indicated by the eigenvalue analysis resultants of C and K. Interestingly, grainsremain or become more angular over the million-year time scale of the study as they decrease in size, indicating active in situ weathering processes on individual grains; this result is counter to the common assumption that as grains weather they become more rounded over time.
Toe-cut terraces Larson, Phillip H.; Dorn, Ronald I.; Faulkner, Douglas J. ...
Progress in physical geography,
08/2015, Letnik:
39, Številka:
4
Journal Article
Recenzirano
Alluvial fans and fluvial terraces occur in nearly all climatic settings and often coexist within the same drainage basin. These landforms play an important role in understanding the geomorphic, ...hydrologic, sedimentologic and erosional histories of a basin. The juxtaposition of fans and fluvial terraces, in some instances, can lead to misinterpretation in distinguishing traditional fluvial terraces from the truncated toe of tributary alluvial fans. This becomes particularly troublesome for those attempting to interpret results from published field studies where fan-cut terrace, truncated alluvial fan, toe-cut alluvial fan, alluvial terrace, and incision of the lower end of a fan piedmont all refer to the same genetic landform. We call for use of the term “toe-cut terrace” to represent this landform. We also present criteria to aid in the identification of toe-cut terraces, defined as an abandoned alluvial surface, formed by the truncation of the distal portion of tributary alluvial fans by streams flowing obliquely or perpendicular to the fan surface. Truncation occurs through lateral erosion (“toe-cutting”) or through vertical incision by the trunk drainage lowering the base-level of the alluvial fan. This results in incision into the fan surface abandoning the fan’s depositional surface at a higher level above the modern floodplain – a form that often resembles a fluvial terrace. A case study from the Sonoran Desert in central Arizona illustrates a sequence of abandoned alluvial surfaces that resemble fluvial terraces, but use of the proposed criteria reveal the presence of both toe-cut terraces and traditional fluvial terraces formed by the abandonment of the rivers former floodplain.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, ODKLJ, OILJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Based on research from slopes on rhyolite domes of known age formed over a million-year continuum in eastern California, a classic geomorphic debate is reconsidered and a general model of desert ...slope development proposed. This study examines steep (∼25° to ∼35°) boulder-dominated slopes that include well, varnished, vertically oriented colluvial deposits. Such deposits are common throughout the arid southwestern United States. Basic field and isotopic dating methods are combined with two surface-dating techniques, cosmogenic chlorine-36 and rock varnish microlaminae, to produce a detailed slope development history with broad implications for geomorphic theory that includes the unresolved geomorphic debate between Walther Penck and William Morris Davis.
Slopes in this study are dominated by the on-going desert slope processes of debris flows and in-situ grain disintegration as evidenced by active debris flow features, terminal Pleistocene ages of microlaminae, and chlorine-36 ages progressively younger than potassium-argon ages for slope genesis. Results also indicate that slopes retreat in a parallel fashion as postulated by Penck. Furthermore, the deposits do not exhibit significant changes in grain size, shape, or angularity from genesis to ∼0.6 Ma but change markedly after that time possibly indicating a geomorphic threshold between ∼0.6 and ∼1 Ma, or episodic erosional events throughout the mid to late Pleistocene.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
9.
Evolution of desert colluvial boulder slopes Friend, Donald A; Phillips, Fred M; Campbell, Sean W ...
Geomorphology (Amsterdam, Netherlands),
12/2000, Letnik:
36, Številka:
1
Journal Article
Recenzirano
We employed rhyolite domes formed during the past million years in eastern California to study the evolution of boulder-dominated slopes. The slopes studied are steep (from ∼25° to ∼35°) and are made ...of coarse, boulder-sized blocks. These slopes include well-varnished vertically-oriented colluvial deposits that appear similar to relict periglacial stone stripes. In this case, they are the result of ongoing desert slope processes. Such deposits are common throughout the arid southwestern US, but their morphometric character, fabric and rates of formation have not been assessed systematically. Basic field and isotopic dating methods are combined with two relatively new surface dating techniques, cosmogenic chlorine-36 and rock varnish microlaminae, to produce a detailed million-year-long slope development history with broad implications for geomorphic theory. Grain size, grain shape, grain angularity, and slope deposit area do not change significantly from genesis to ∼0.5 Ma; trends in the data change markedly after that time. A geomorphic threshold occurs between ∼0.5 and ∼1 Ma. as indicated by significant changes in all parameters but grain orientation data. On-going erosion over the million-year continuum is evidenced by active debris flow features, by terminal Pleistocene ages of microlaminae on all deposits, and by
36Cl ages that are progressively younger than potassium–argon ages for slope genesis.
We report the use of environmental scanning electron microscopy (ESEM) to determine the phase separation in the cross-section of a
200
nm
thick polyfluorene blend film, of the type used in polymer ...photovoltaic devices and LEDs. The micron and sub-micron surface phases are found to penetrate through the film to the underlying substrate, whilst smaller surface features do not necessarily propagate through the film. The observed cross-sectional structure helps to explain the optoelectronic response of these blends and shows that ESEM is an effective tool in the characterisation of polymer blend cross-sections.
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