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ژئومورفولوژی

مفاهیم کلیدی در ژئومورفولوژی پیشرفته


مفاهیم کلیدی در ژئومورفولوژی پیشرفته

culture
the distinction between English-speaking geomorphologists (process, geotechnical, quantitative, applied) versus other scientific cultures (e.g. mapping, climatic, soil in Europe)
time
geomorphic processes have occurred throughout earth history and are expressed in the sedimentary structures, however geomorphology as a discipline is the study of late Cenozoic landforms (Tertiary and Quaternary Epochs)
geomorphologists study of landscape evolution at longer than human lifespans but very much shorter than the entire geologic record
explanation is nearly always of past evolution rather than prediction of future change

space
similarly the spatial domain is limited to the sub-continental scale (submarine studies are part of oceanography)
large-area studies are in the realm of physiography, regional geomorphology, denudation chronology, climatic geomorphology and mega-geomorphology

process
geomorphologists (especially English-speaking) focus on exogenic processes
they rely on geological principles (i.e. plate tectonics, isostasy) for the interpretation of endogenetic landforms

 

morphology and sediments
whereas the study (description, measurement, modelling over time and space) of morphology is uniquely geomorphological, investigation of internal structure overlaps with sedimentology, Quaternary geology/stratigraphy, and soil science

 

soil
over most of the earth's surface, the dominant physical processes are pedological (soil-forming rather than land-forming processes)
however there is considerable overlap among soils, weathering, erosion, sedimentation and topography (catenas), and the ages of buried soils and geomorphic history

thus there is much to be learned at the interface of pedology and geomorphology and soil geomorphology is an undervalued field of study

morphology
based on the idea that the measurement and classification of shapes will provide insight into the evolution of landforms (similar for looking at the texture and structure of sediments)
stems largely from work of hydrologists (especially R.E. Horton) working on drainage networks, and geographers (especially A.N. Strahler) working on slopes and drainage basins, starting with the quantitative revolution in geography
initially most data were extracted from maps, but now remote sensing, GIS and DTM (military work in the 60's), offer great potential for morphometric analysis with high resolution over large areas (possibly even detecting changes in form over time)

 

climatic geomorphology
based on the idea that there are recognizable sets of landforms and geomorphic processes associated with different climatic regimes
significant methodology in French and German geomorphology

characterized by emphasis on classification and orphological studies and a lack of process research and theoretical foundation

applies best to extreme climates (deserts, glacial, periglacial) and provides poor explanation of structural and polygenetic landscapes (i.e., in response to climatic change)

 

process geomorphology
the dominant approach in English geomorphology over the past several decades
mesoscale, statistical, emphasis on temporal and spatial variation in process rates

dominated by field studies where rates of transfer of water, wind, ice and sediment are used to infer geomorphic processes in lieu of direct observation

thus active (high-energy) landscapes (badlands, mountains, beaches, periglacial landscapes) have attracted much research in the past several decades

contemporary geomorphic theory has developed over the past several decades as a conceptual framework for process geomorphology

 

geotechnical science (engineering geomorphology)
a by-product of process geomorphology as more knowledge is required about material properties and the detailed mechanics of processes
relies heavily on, and moves geomorphology towards, civil engineering (soil and rock mechanics)and soils science

problems with scale linkage and thus generalization from the laboratory to landforms and landscapes

 

applied geomorphology
application of geomorphology to contemporary environmental and social problems (making geomorphology relevant)
includes aspects of process geomorphology, geotechnical science, environmental studies, resource management, soil conservation, hazards studies

typical of most research in public institutions

focus on human timescales and not necessarily at timescales of landform evolution, thus it either draws geomorphologists away from questions central to the discipline or requires considerable thought about time scale linkages


Conclusion

the dominance of process and applied geomorphology (and thus geotechnical studies), created a focus on the site scale, and neglect of regional synthesis
we have gone beyond the mesoscale (and thus landscape models) into the realm of engineers
geomorphologists have tended to align themselves with engineers or geophysicists or sedimentologists rather then with colleagues in their own discipline causing fragmentation, lack of connection to the academic roots in geography, lack of focus on the primary goal: explanation of the evolution of landscapes (see Baker and Twidale, 1993; Ritter, 1988)


Terminology

besides the use of mathematics to express theory, ideas and philosophy are expressed in native (spoken) language
natural (everyday) language is flexible and dynamic, but therefore also ambiguous
natural language is too ambiguous for some disciplines (e.g. math, logic) so they create their own languages
scientific definitions have to be precise
words used to represent constructs (e.g. apple) are defined in terms of classification (apple is a fruit)
words used to represent concepts (e.g. stress) are defined relative to other concepts which collectively comprise laws and theory
the most theoretical disciplines have the most rigorously defined terminology; the development of theory in geomorphology is constrained by imprecise terminology
scientific language has the weaknesses of natural language (ill-defined, misused, misunderstood, ambiguous, changing terminology), plus the listener may not be aware of a term if he/she does not subscribe to the same philosophy methodology: "each theoretical view of geomorphology has created its own language" and views become reinforced by virtue of a unique vocabulary
does the content of thought (words) influence the thinking process; contemporary view: the structure of a language influences perceptions of reality
there should be separate terminology for description and interpretation because these are separate stages of the scientific method
however genetic classification of landforms is common and thus terms use to describe landforms convey their origin (interpretation)
thus a scientific approach to geomorphology is not well-supported by the use of existing terminology

 

problems with existing terminology:
morphogenetic terms: include an interpretation of origin
landforms are often polygenetic (e.g., slope processes on a landform of tectonic or glacial origin)

descriptive terms are more specific (less scope) and thus less subjective (interpretive)

e.g.,
peneplain: the ultimate stage of the cycle of erosion

surface, alluvial fan, till versus diamicton

 

inadequately defined terms
with standard definitions, terms are used differently by different schools of geomorphologists
e.g. ,
nivation: uncertain number of weathering and transport processes affected by snow

solifluction: may or may not be applied to permafrost (gelifluction); Anderson (1906) working in the Falkland Islands did not refer to permafrost in the original definition
 standard definition of landform; in reference books it is either not defined (Goudie, et al., 1985, Encyclopaedic Dictionary of Physical Geography) or defined in a general way in terms of shape ("consistency of form", "the relative position of points on an outline or external surface")
but geomorphologists usually think of a landform as having both distinct shape and internal structure

 

evolving terms
the evolution of terminology reflects a compromise between the need to revise or create concepts and the limited ability of human beings to learn and memorize terminology

therefore, new terms are introduced and adopted only when existing terms are inadequate

as terminology evolves, meanings change or terms develop more than one meaning so that their use has to be explained, which is contrary to the purpose of scientific terminology (shorthand)

e.g. ,
periglacial: originally "next to glaciers", now also used in the sense of conditions that exist near glaciers

morphogenetic terms are subject to redefinition or multiple use as the origins of landforms are re-evaluated, e.g. ,drumlins (molding of drift or subglacial meltwater flood?)

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