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The Nature of Mountain GeomorphologyAuthor(s): Dietrich Barsch and Nel CaineSource: Mountain Research and Development, Vol. 4, No. 4, High Mountain Research.Proceedings of a Workshop of the Arbeitsgemeinschaft für VergleichendeHochgebirgsforschung in December 1982 in Munich (Nov., 1984), pp. 287-298Published by: International Mountain SocietyStable URL: http://www.jstor.org/stable/3673231 .Accessed: 20/09/2011 18:03

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Mountain Research and Development, Vol. 4, No. 4, 1984, pp. 287-298

THE NATURE OF MOUNTAIN GEOMORPHOLOGY

DIETRICH BARSCH1 AND NEL CAINE2

ABSTRACT A century of study suggests many common characteristics in the geomorphic nature of high mountain areas. These include important structural influences in the landscape, usually on a variety of spatial scales, and contrasting climatic conditions

(often confounded with vegetation distributions) which also exhibit a wide spatial variability. Most high mountain terrain also shows evidence of ancient erosion surfaces as well as that of past glacial action and other, less direct, consequences of late-Pleistocene environmental changes. The resulting landscape is one of high relief and highly variable potential energy. This is reflected in a history of recent erosion by large catastrophic events and a high potential for accelerated erosion where mountain terrain is impacted by man's activity. Such common characteristics suggest that mountain geomorphology be considered as a "regional" component within

geomorphology.

RESUME La nature de la geomorphologie montagnarde. Pendant un siecle de nombreuses analogies de formes et de processus geomorpho- logiques ont ete mis en evidence. Ce sont les influences et les donn6es structurales (Tektovarianz) et les variations des conditions

climatiques avec l'altitude, qui sont les plus importantes. Les 6tages climatiques sont visibles dans la repartition de la v6g6tation, qui montre une enorme variabilit6 spatiale. A c6te de la dynamique r6cente, les stades anciens de I'&volution du, relief (Relief- generationen), par example les restes d'anciennes surfaces d'6rosion, les formes glaciaires du Pleistocene et les temoins tardiglaciaires, moins visibles, de l'6volution du paysage, ont une grande influence sur le physionomie des hautes montagnes. La dynamique r6cente est aussi fonction de la raideur de pente. C'est pour cela qu'on trouve ici des ev6nements g6omorphologiques catastrophiques et aussi une tendance vers une erosion acc6l6r6e caus6e souvent par l'homme. La g6omorphologie des hautes montagnes peut etre consid6r6e comme une composante rigionale de la g6omorphologie g6nerale.

ZUSAMMENFASSUNG Die Beschaffenheit der Geomorphologie im Hochgebirge. In mehr als einem Jahrhundert Hochgebirgsforschung sind viele Gemeinsamkeiten in der Gestalt und in der geomorphologischen Formung der Hochgebirge der Erde erkannt und bearbeitet worden. Dazu geh6ren neben den wichtigen strukturellen Einflfissen und Gegebenheiten (Tektovarianz) vor allem die recht wechselhaften klimatischen Bedingungen, die sich meist im Vegetationsmuster widerspiegeln und die Ausdruck einer enormen raiumlichen Variabilitit sind. Von grogem Einfluf auf die heutige Gestalt der Hochgebirge sind auBerdem die frfiheren Reliefzustande (Reliefgenerationen). Hierher geh6ren neben den meist hochliegenden Relikten alter Erosionsflichen vor allem der fossile pleistozdine glazigene Formen- schatz wie auch die meist weniger aufflilligen Zeugen des spditpleistozdinen Landschaftwandels. Das Hochgebirgsrelief is so durch Steilheit und durch eine hohe, von Punkt zu Punkt jedoch hdiufig schnell wechselnde potentielle Energie gekennzeichnet. Ausdruck dieser Verhiiltnisse ist das Auftreten gr6i3erer, katastrophaler geomorphologischer Ereignisse und eine hohe Bereitschaft zu akzelerierter Erosion bei unsachgemdiien anthropogenen Eingriffen. Alle diese gemeinsamen Charakteristika bestditigen, datf die Hochgebirgsgeo- morphologie als eine regionale Komponente der Allgemeinen Geomorphologie anzusehen ist.

INTRODUCTION

Recent decades have witnessed an exponential growth of scientific research in mountain environments at a time when man's impacts on them has also accelerated. Such

growth in scientific interest in mountains is clearly indi- cated by the publication of texts such as Ives and Barry, 1974; Barry, 1981; and Price, 1981; in the appearance of entire journals (not just special issues) devoted to mountain environments (e.g., Arctic and Alpine Research; Moun- tain Research and Development; Revue de Gdographie Alpine; Studia

Geomorphologica Carpatho-Balcanica; Zeitschriftfiir Gletscherkunde und Glazialgeologie) and in the growth of other publications

in environmental science. This paper is intended to be a statement on the nature of mountain geomorphology, which is considered as a special theme of general interest within geomorphology, with broad regional aspects. The authors intend it to be a pragmatic definition of mountain

geomorphology, emphasizing the research themes which have been pursued and their significance, rather than a

prescription of what this subject should be. The geomorphically important characteristics of the

mountain environment define many of the concerns and

concepts basic to mountain geomorphology and so are the first to be discussed here. They lead to the main themes followed and discussed in previous work on mountain geomorphology. Here the dichotomous nature of geomorphology itself provides the basic distinction between work con-

cerning the landforms of mountains and that involving the

'Geographisches Institut, Universitiit Heidelberg, D-6900

Heidelberg, Federal Republic of Germany. 2Institute of Arctic and Alpine Research and Department of

Geography, University of Colorado, Boulder, Colorado, U.S.A.

288 / MOUNTAIN RESEARCH AND DEVELOPMENT

study of land-forming processes in the same environments. These two may be further subdivided in the tree-form of

Figure 1 to give the four recurrent themes in mountain geomorphology described elsewhere (Caine, 1983). In the conclusion to this paper, three general statements are put forth:

(1) an empirical evaluation of the aims of mountain

geomorphology; (2) a statement of future needs and research in the subject; and (3) a rationalization of it in terms of its applicability to environmental management.

GEOMORPHOLOGY

MOUNTAIN GEOMORPHOLOGY

MOUNTAIN FORM MORPHODYNAMICS IN MOUNTAINS

MORPHOMETRY RELIEF MORPHOCLIMATIC PROCESS DYNAMICS a GENERATION MODELS a

STRUCTURE a HISTORY ACTIVITY

FIGURE 1. Research themes in Mountain Geomorphology. This figure emphasizes dichotomous branching among broad topics of research and ignores, for simplicity, the (horizontal) interaction between these topics.

MOUNTAINS AND MOUNTAIN GEOMORPHOLOGY

Any attempt to define mountain geomorphology confronts two problems at the outset, both evident in the name of the subject. First, as part of the broader science of geomorphology, mountain geomorphology must seek to accommodate itself to the dichotomous nature of geomorphology. Recent work in geomorphology has strongly emphasized the study of geomorphic processes, occasionally with the pious expectation that this would lead to an understanding of landforms, but more usually as an end in itself (Chorley, 1978). In contrast, classical views of geomorphology emphasize the study of landforms, the history of the landscape in which they are set, and the search for models of relief development. Landforms are rarely the products of the processes which now act upon them (Ander- son and Burt, 1981), and then only at the smaller spatial scales, in pico-, nano- and micro-forms. The disparity between present landforms and contemporary processes is especially evident in mountain areas: it was, after all, in these areas that the evidence of Pleistocene glacial advances was first recognized, evidence that is everywhere an important part of mountain scenery.

A second problem of definition to be faced in an evaluation of mountain geomorphology is that due to the term "mountain". In many respects, this is the problem which confronts any attempt to define a regional boundary which is not based on administrative convenience. For mountains, the problem of definition has been approached many times in the past century (e.g., Penck, 1894; Krebs, 1922; Troll, 1941, 1972; Ives and Barry, 1974; Price, 1981). Here, this

question is considered briefly but with the view that the definition of the approaches and topics central to mountain geomorphology is more important than the demarca- tion of boundaries. The latter will always be diffuse and will often be redefined in terms which are most apposite to the particular problem faced by individual researchers.

Even the most commonplace definition of "mountain" is one that has significance to the geomorphologist. It is

likely to include reference to at least four characteristics of mountain terrain that are important in describing landforms or the processes acting upon them. These are: (1) elevation, often in absolute terms; (2) steep, even precipi-

tous, gradients; (3) rocky terrain; and (4) the presence of snow and ice.

Some of these characteristics have been used to differ- entiate between mountain environments in a semi-quantitative manner (Table 1). In this case, change in elevation or relative relief is used to define successively more mountainous environments. Other characteristics, controlled by elevation, relief, and topography, have also been

suggested in definitions of mountain terrain. Thus, Troll in a series of papers (1941, 1954, 1972, 1973) suggested that climatic-vegetative belts are diagnostic. In this scheme, a high-mountain system is one which extends above timberline whilst a mountain system is one which

encompasses more than one vegetation belt but does not extend to an alpine elevation. Although it is defined in terms of vegetation (Zech and Feuerer, this issue, pp. 331-338), this is clearly consonant with a morphoclimatic approach to mountain geomorphology. It has, however, some shortcomings, especially in environments where "timberline" is not easily defined (for example, in polar [Stiiblein, this issue, pp. 319-330] and arid regions and on high tropical mountains).

Other features of the mountain environment are not

recognized explicitly in these statements, although they may be vital to a geomorphic understanding of mountains. Four of these are worth noting here. First, mountain areas are internally diverse and variable - a variability that derives from their elevation, relief, and exposure. Second, most mountain systems show clear evidence of late-Pleisto-

TABLE 1 Relief contrasts in different types of mountain systems

Altitudinal difference Relative

Type (over 5 km distance) relief

High mountain system > 1000 m 500 m/km2 Mountain system 500-1000 m 200 m/km2 Mountainous terrain 100-500 m 100 m/km2 Hilly terrain 50-100 m 50 m/km2

D. BARSCH AND N. CAINE / 289

cene glaciation. Third, many mountain areas, and especially the highest of them, remain tectonically active today and in some cases rates of tectonic uplift exceed those of

degradation and erosion (Schumm, 1963). Finally, many mountain environments appear to exist in a metastable state such that they are particularly vulnerable to dis- turbance.

These characteristics combine to define a geomorphic environment which has attracted much attention. This work has been directed, on the one hand, to the evolution of landforms and their associations or, on the other hand, to the controls of geomorphic processes and their magnitude and interaction. The scientific problems of mountain areas remain as challenging as the terrain itself.

HIGH MOUNTAIN RELIEF AND LANDFORMS

Mountain and high mountain systems like the Alps, the

Rocky Mountains, and the Himalaya have landscapes dominated by vertical relief. Even though the absolute difference in elevation (about 20 km) between ocean trenches and the highest summits is slight in comparison to the earth's diameter, mountains and their relief have always been important to human use of the earth.

In a geomorphic context, mountainous terrain forms one of the main relief elements on the earth's surface (Figure 2). Dongus (1980: 136) defines four relief elements: (1) old shield lands such as the Canadian Shield and most of Aus-

tralia; (2) uniform plains and table lands with approxi- mately horizontal sedimentary rock structures; (3) large alluvial plains such as the lower Amazon basin; (4) the mountain and high mountain systems. Because of their size and their influence on life and climate, mountain systems are among the megaforms of the earth's surface (Barsch and Stfiblein, 1978), with a special relief that reflects a long period of tectonic-geologic-geomorphic development. For this reason, high mountains are usually characterized by complex geologic structures associated with intense fold-

ing and faulting; by tectonic activity during Tertiary and

1800 15o0 1200 900 600 300 6o 00 0o " 900 1200 1'500 1800 1500

0 continental shields

30 300

table lands

mountain systems

• mountain -/high : mountain -systems

oo .. . s d

so00.....

15 0? . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .......... ...

B~ii~i~l iiiiii i0 ......~~, ............i~ii.i~i~i~iii

FIGURE 2. The major relief elements of the earth's terrestrial surface (Dongus, 1980).


even Quaternary times (Fairbridge, 1968; Rathjens, 1982), and by high erosion rates which are a consequence of recent uplift (Garner, 1959; Young, 1969). Further, this erosional

intensity has been augmented during the Pleistocene by increased glacial activity in nearly all high mountain areas. In many high mountains, the balance between erosion and tectonic uplift is often resolved in favour of the latter (Schumm, 1963). For example, the Bergell granite of the southeastern Swiss Alps which was formed only 30 million years ago at a depth of about 30 km (Chessex, 1962) is now exposed at the surface. This suggests a mean erosion rate of 1 mm/yr for a geologic time scale, a rate generated by an even greater magnitude of tectonic uplift.

HIGH MOUNTAIN SYSTEMS

In high mountain systems, the elevation range between summits and valley floors is normally more than 1,000 m

(Penck, 1894; Krebs, 1922; Hammond, 1964; H6ller- mann, 1973; Barsch and Stfiblein, 1978). Often, more than 2,000 m of relief occurs across horizontal distances of only a few kilometres. Ford et al. (1981) show a mean relief of 1,340 m (with standard deviation of 400 m) in 200 ran- domly selected 10 x 10 km quadrangles in the southern Canadian Rocky Mountains. In the Alps, Hormann (1965) lists 11 passes which are more than 2,000 m lower than the summits on the drainage divide crossed by the pass. He uses these deeply incised passes to subdivide the Alps into major mountain groups (Figure 3) which form clear geomorphic units, even if they are not genetically distinct.

High mountain areas, therefore, are characterized by a steep topography, dominated by rock walls (of more than

60') and steep slopes (between 35 and 600), even where flat valley bottoms and high plateaus occur. Apart from the work of Evans (1972) and that of Ford et al. (1981), there have been few statistical analyses of relative elevation and slope (the first derivative of elevation) in mountain areas, although the continued development of data bases and sources (Finsterwalder, this issue, pp. 315-318) suggests that quantitative comparisons on a wide scale may soon be possible. However, it is not yet possible to distin-

guish unequivocally between high mountain systems and mountain systems on morphometric grounds (Figure 2). Qualitatively, it is suggested that steep rock walls are diagnostic of high mountains whereas slopes steeper than 350 are relatively infrequent in mountain systems. This, with a relative relief of more than 1,000 m for the former, allows a morphographic distinction between the two.

In the Alps and other high mountain systems, rock walls and steep slopes are normally due to.glacial erosion which has also produced a set of bedrock forms (such as horns, aretes, cirques, and glacial troughs) characteristic of almost all high mountains (Figure 4). In addition, post-glacial talus

slopes and fans of debris from the rock walls usually dominate the valley floor scenery. Except for a few high-level surfaces (usually on limestone in the Alps) areas of low relief exist only on the "shoulders" of glacial troughs (Trogschulter) as remnants of Tertiary terraces (Annaheim, 1946) and on the floors of valleys filled with fluvial sediments. Not all high mountain areas conform to this model: in the southern Rocky Mountains, for example, sharp bedrock ridges and horns occur alongside wide, rounded interfluves and

flat-topped mountains (Figure 5) which are usually ex-

/Dachstein Hochkon.

,A

/ Mt. Blanc

.Mt.Rosa

hi

,0 200km

FIGURE 3. The mountain groups of the Alps. Major drainage divides are shown by the broken line and the most important peak in each group is identified (Hormann, 1965).


horn

rockwall

+cirque

+. + trough-shoulder

+ + +

\rb.

+ rockwall

trough

+ r

. .DL -.. -- ' - -

FIGURE 4. The basic elements of Alp-type relief.

(some) horns

interfluve

+, rockwall + cirques

e cirqooues

volley floov

FIGURE 5. The basic elements of Rocky Mountain-type relief.

plained as the remnants of former erosion surfaces (Scott, 1975).

Other high mountain areas which do not fit the model of Figure 4 include those of semi-arid and arid regions (H61lermann, 1973). Hd11ermann concludes that the mountain ranges of the Great Basin, for example, are high mountains in the true sense, despite the fact that they do not reach timberline and were only lightly glaciated during the Pleistocene. On the other hand, they are remarkably steep, with more than 1,000 m of local relief, because of recent tectonism and deep dissection which has created steep- walled gorges. Similar landscapes are found in other mountain systems of the arid zone, e.g., in the Tibesti (Hover- mann, 1963). In these landscapes, the Richter denudation slope (at 30 to 350) is an important form (H611ermann, 1973), and one that contributes to a different assemblage of landforms than those shown in Figures 4 and 5. This assemblage lacks glacial features almost entirely but nevertheless forms a high mountain landscape.

In polar regions, mountains which carry all the landform evidence of intense glaciation are common, although the local relief is often less than 1,000 m. This case, too, is an exception for there can be little question of the "high mountain" nature of such landscapes.

Thus, the dominant morphologic characteristics of a high mountain system are its steepness and its altitudinal range. Both of these are important influences on geomorphic processes. Within this classification, two relief types are dis- tinguished: the "Alp Type" and the "Rocky Mountain Type". The first of these is associated with an overriding impact of glacial ice and very marked effects of glacial erosion. The second involves a less pervasive impact of glacial erosion and includes important areas of low relief on flat summits and rounded interfluves. Further, also included as high mountain areas are two situations which may not have more than 1,000 m of local relief or may not rise above timberline: polar mountains and desert mountains, respec- tively.

RELIEF DEVELOPMENT IN HIGH MOUNTAINS

In addition to the larger landform associations described above, the relief of high mountain systems often shows smaller internal regularities. Thus, the major valleys often follow lines of structural weakness which can be traced over long distances, as for example the line of the Rhone-Reuss- Vorderrhein in the Alps. Such regularities have featured in many discussions of relief development in high mountains and it is not possible to quote more than a few cases here.

Dissection of the landscape has long been considered important in the development of a high mountain system and much effort has been expended in attempts to distin- guish the fluvial and glacial contributions to this (S61ch, 1935). Accordant surfaces and elevations which might mark different stages in the development of high mountain terrain have been recognized. Four such levels have been identified in many high mountain systems:

1. the alpine summit accordance or gipfelflur 2. the alpine crest and summit accordance 3. the timberline and alp slope accordance 4. the benches along major valleys.

The accordant elevation of most summits in a mountain group has long been recognized (Penck, 1919; Heim, 1927; Pannekoek, 1967). The summit accordance in the western U.S.A. lies about 600 m above present timberline (Thomp- son, 1968) and, like some of the lower accordances, has been explained by one of two alternative hypotheses. First, there is the view that the gipfelflur consists of remnants of an old erosion surface, either a peneplain (Willis, 1903) or a pediplain (Bradley, 1936). In the Alps, similar surfaces have been explained as relics of a landscape which was only slightly dissected, perhaps similar to a middle mountain system (Mittelgebirge) such as the Black Forest (Annaheim, 1946; Annaheim and Schwabe, 1959).

In contrast, the same accordances have been explained by other workers as the product of regular patterns (in space and depth) of dissection which constrain summits to ap- proximately the same elevation. These opposed views appear in many discussions of mountain landscapes pub-


N ilne of tectonic uplift S

Cm)--- ------- - (M urnmrrlt PCccorce)CC

3000G

A... summit

. Reuss Tessin

2000 , -

R ,.,- ?. -"???r '

,.•

..1000-.. .. .

0Be *-Pu ...

. ... 7

0? : .....:: ...............

...

300 .. ... .. ............. ..

Flueten Amsteg Andermatt Arioto Faido Locarno

FIGURE 6. Cross-section through the Swiss Alps along the line Tessin-St. Gotthard-Reuss (Anna- heim, 1946). The alpine summit accordance (Gipfelflur) is shown. Pe-Pettanetto Terrace System; Be - Bedretto Terrace System; Pu - Pura Terrace System; G - St. Gotthard region.

lished in the last 100 years such as the discussion between Russell (1933) and Atwood and Atwood (1938).

A variant of the erosion surface hypothesis is the view of Thompson (1968) that the summit level represents an

interglacial alp slope associated with a higher timberline than the present one, and the contrasting intensities of erosion processes above and below it. According to this model, the crest and summit accordance, which Thompson iden- tifies at elevations about 300 m above present timberline, reflects the position of Pleistocene timberlines.

Benches along the sides of major valleys and the timberline and alp-slope accordance (at the elevation of present timberline) pose serious problems. They are readily recognized and are often explained in part by local geological structures, though structure cannot be the only explana- tion of their development. Unfortunately, none of these benches carries sediments older than the last glaciation. Three explanations of such benches have been suggested by earlier workers:

1. That they are the relics of fluvial valley floors, represent- ing a stage in a long history of valley deepening and dating from the Tertiary.

2. That they are erosional forms produced by Pleistocene

valley glaciation which has been partly controlled by older terraces and geologic structure.

3. That the timberline bench, at least, is a response to the contrast in the intensity of mass wasting and erosion above and below timberline (Thompson, 1968).

A choice among these three is not possible, and they may not be mutually exclusive. However, the general problem from which they derive, that of valley deepening, is a cru- cial one in work on the development of mountain relief, and one which has attracted much attention (S61ch, 1935). Annaheim (1946) used the heights of tributaries above the

main valley and the elevation of cirques to reconstruct three

major benches along the Ticino valley, southern Swiss Alps (Figure 6). These three levels (the Pettanetto, Bedretto, and Pura terraces) are thought to be of early, middle, and late Pliocene age (from highest to lowest). In addition, Annaheim demonstrates that the Pleistocene glacial trough of the Ticino, which approximates the elevation of the

valley glacier of the last glaciation, cuts across all three terrace systems. The bench above the "trough-shoulder" (Figure 4), which has often been considered to be the

youngest pre-Pleistocene terrace, is shown by this analysis to be much older and to reflect a variety of stages in relief

development, rather than a single one. It is unlikely that the Pleistocene trough and its upper limit (the "trough- shoulder") should correspond to the same terrace in all parts of the Alps. Annaheim's study suggests that it might be

possible to recognize benches of Pliocene age in the valleys of high mountain systems and that some of the relief elements in the mountain scenery are of much greater an-

tiquity than is commonly thought. A more recent indica- tion of this antiquity, and one which is supported by absolute dating, is found in the work of Ford et al. (1981) in the southern Canadian Rocky Mountains. These workers

suggest that the age of the present relief is between 6M and 12M years, i.e., of Pliocene age. Some relief elements in the present landscape may be even older than the Plio- cene, although it may be difficult to demonstrate such an

age conclusively (Caine [1983] suggests that the general form of some Tasmanian mountains has not changed since the Eocene). Nevertheless, despite the antiquity of major relief forms in high mountain terrain, it is safe to assume that most of the landscape is no older than the Pliocene, and almost all of that which is of interest in geomorphology is much younger than this.

MOUNTAIN GEOMORPHIC PROCESSES

Few of the geomorphic processes presently acting in the mountain landscape are restricted to that environment;

most of them are found in other environments as well. However, the combination of morphodynamic processes


and the intensity and rate at which they act may be clearly different from those found elsewhere. This difference has provided a reason for scientific research in all mountain ranges of the world in the last few decades (Price, 1981). This discussion consists of two parts. First, the general nature of the morphodynamic system in mountain areas is considered. Following this, three case studies of contemporary geomorphic activity in different mountain systems are summarized.

THE MORPHODYNAMIC SYSTEMS OF HIGH

MOUNTAIN AREAS

The high relief and steep slopes which are the distin- guishing characteristics of mountain terrain provide much potential energy for erosion and sediment transport. This potential is translated in turn into the rapid erosion rates which have long been recognized as typical of mountain regions (Fournier, 1960; Schumm, 1963; Young, 1969). In addition to local relief, other environmental factors con- tribute to the high rates of denudation in mountain areas. These include low temperatures and increased precipitation amounts, and the associated hydrologic and vegetational contrasts with lowland areas. They also include a common

correspondence with tectonic activity in the form of vol- canic and seismic disturbances. A Pleistocene history of environmental change, most obviously in the glacial influences which account for many precipitous slopes, provides a further common characteristic of almost all high mountain areas.

It is also important to recognize the great morphodynamic variability of mountain systems. A high mean rate of erosion is the product of events that are episodic in time and discontinuous in space. Some part of the temporal variability is predictable through its association with the diurnal

temperature cycle (Fahey, 1973; Luckman, 1976) or with the seasonal cycles of freeze-thaw and streamflow (Bene- dict, 1970; Caine, 1976; Thorn, 1976). Apart from these

periodic regularities in the temporal pattern of geomorphic activity, much of the geomorphic work performed in alpine and mountain environments seems to be infrequent and

essentially random in its timing. The resulting pulsed impacts on the erosional and sediment transport systems dominate most records of contemporary slope development in mountains (Rapp, 1960; Grove, 1972; Caine, 1976). They are often associated with intense rain from unusual

meteorologic conditions (Tricart et al., 1961; Starkel, 1972; Balog, 1978) or with seismic events (Sharma, 1974: Chap- ter 6; Hadley, 1978; Plafker and Ericksen, 1978; White- house, 1981). In both cases, recurrence intervals on the order of 102 to 104 years suggest that the systems are strongly controlled by transient behaviour like that described by Brunsden and Thornes (1979).

This temporal variability is matched by an equivalent spatial one which is most evident in high mountain systems of the Rocky Mountain type. In this terrain type, enclaves of low relief, on which there has been little landscape modification for millenia, are interposed with steeper slopes on which rapid, contemporary change occurs. Even in high mountains of the Alpine type, most of the geomorphic work of sediment movement is achieved within

small parts of the total area (Caine and Mool, 1982). Com-

monly these partial areas of greatest activity are steep slopes, sites where the winter snow cover is concentrated and areas of glacier activity. Increasingly, they are those

parts of the landscape in which human impact on soil and

vegetation is greatest. For whatever reason, the spatial vari-

ability of mountain erosion and sediment transport is fre-

quently reflected in the vegetation and soil distributions, which in turn feed back to the variability in erosion

(Summer, 1982). The process systems which operate in alpine environ-

ments have been described by Caine (1974) as a cascade of sediment fluxes involving a variety of materials and controls. Some of these fluxes have received much attention from researchers while others have been almost ignored. They, too, are variably distributed in the mountain landscape although it may be possible to define general patterns in their relative significance (for example, with respect to elevation: Caine, 1984). A four-way classification of mountain process systems is suggested, with different controls, responses, and levels of activity. This distinguishes the mountain glacial system, the coarse debris system, the fine clastic sediment system, and the geochemical system. This distinction is not intended to suggest that these four fluxes do not interact, nor that material does not move between them during landscape development. Of the four, the mountain glacier and the coarse debris systems are most characteristic of high mountain terrain for they tend to be restricted to areas of greatest elevation and relief.

The Glacial System The distribution of mountain glaciers clearly reflects

their control by elevation and climate which influence the mass balance and thus the equilibrium line altitude and the glaciation limit (Ostrem, 1974). In general, this system is found at the highest elevations, where the movement of water in the solid phase is important in the transport of debris derived from rockfall as well as from erosion at the ice-rock surface. This is a physical system with relatively high power (Andrews, 1972) and one which is effective in debris transport, at least to the glacier margin where depo- sitional forms that are diagnostic of this system, and its interaction with the fluvial system, are found. In presently glacierized mountain areas, the glacial system is a dominant influence on erosional activity (Embleton and King, 1975: Chapter 11), though great changes in the intensity of that activity reflect lesser changes in the glacier mass

(Reheis, 1975).

The Coarse Debris System This system also includes many of the landscape com-

ponents that are characteristic of high mountain terrain. It involves the transfer of coarse detritus between cliffs and the talus and associated deposits beneath them as well as the large-scale failure of rock slopes (Heuberger, this issue, pp. 345-362). In maritime mountain ranges, the working of this system may be tributary to the glacial one, i.e., rockfalls are fed into the glacial transport system. In more continental environments, it may be considered as a closed system with down-valley extensions in the form of rock gla-


ciers (Barsch, 1977a). Opening of the system by climatic changes which produce glaciation allows the intermittent removal of accumulated talus as part of glacial tills. An

elevational-temporal continuum of deposits associated with Holocene climatic fluctuations has been suggested on a number of occasions from the deposits of this system (e.g., Richmond, 1962; Madole, 1972; Dowdeswell, 1982).

Most studies have emphasized the dynamics of the talus and rock glacier components of this system. Talus accumulation and shift rates have been estimated by workers in many of the world's mountain ranges (Rapp, 1960; Caine, 1969; Luckman, 1971; Barsch, 1977b; Gardner, 1979; Soderman, 1980). Many of these studies emphasize the

great variability of talus accumulation and movement in both time and space. Even over a few metres, changes by more than an order of magnitude are common. Measure- ments in a variety of environments show that rock glacier motion is more uniform in time, though it may vary across two orders of magnitude according to local geologic and climatic conditions (Wahrhaftig and Cox, 1959; Barsch, 1969; White, 1981). In contrast, the morphodynamic evolution of the source area of coarse debris, the alpine cliffs, has received little attention, perhaps because it appears intuitively simple (Embleton and Whalley, 1979). There are, however, great contrasts in the development of bedrock cliffs, most obviously between those which are influ- enced by rare, large-scale failures and those on which more regular particle falls dominate (Caine, 1983). This contrast may even be propagated into the slope form and the

deposits beneath the cliffs.

The Fine Sediment System In contrast, the cascade of fine sediments through the

mountain system may be considered as an open system. Some of the sediment in this system is derived from aeolian dustfall, in additon to bedrock weathering, and much of it may be exported through the fluvial system to lower elevations. This cascade has received much attention from researchers concerned with mass wasting on alpine slopes (Benedict, 1970; Jahn, 1981). In addition, applied research on the cascade has important implications in areas influ- enced by accelerated soil erosion or where reservoir sedimentation is a concern (Costin et al., 1960; Summer, 1982). In landscapes of the Rocky Mountain type, this system involves mass wasting and surface erosion on the interfluves, as well as on the valley floors, and fluvial transport along stream channels. It responds most clearly to environmental controls involving the hydrologic cycle: to freez- ing and thawing of the ground; to the form and intensity of precipitation and to the distribution of snow on the ground. In wet sites, the resulting rates of mass wasting, by frost creep and solifluction, are much greater than those at lower elevations. However, such rapid rates are not the norm over most of the alpine area with a soil and vegetation cover.

The Geochemical System Except in areas of alpine karst (Bdgli, 1978; Ford, 1971,

1983), there has been relatively little work done on the geochemical exchanges of high mountains. The high quality

of the waters draining from such areas suggests only slight chemical activity and so supports the classical view of the relative insignificance of chemical weathering in alpine systems. However, recent studies support the observations of

Rapp (1960) which suggested that solution weathering in

high mountains is quantitatively important (Thorn, 1976; Vitek et al., 1981; Caine, 1984). In comparison to the mass of material involved in clastic sediment transfers within the high mountain system, the mass in solute trans-

port remains relatively slight. Its importance derives from the efficiency with which solutes are transported and the great flux of water through the environment. This is clearly a system which is responsive to hydrologic controls and reaches its greatest effectiveness in sites that are sources of runoff water, hence its importance in nivation processes where snowdrifts accumulate (Thorn, 1976).

Anthropogenic Influences The influence of man on these sediment transport

systems could be very significant, reflecting the potential energy of the high mountain environment. In many tropical mountains, some of that potential has been realized by agriculture, leading to the acceleration of erosion rates by orders of magnitude (Ives and Messerli, 1981; Caine and Mool, 1982; Hurni, 1982). In mid-latitude mountains, the

anthropogenic impact today is most often derived from rec- reational use of the landscape (Bryan, 1977) and so is fre-

quently concentrated along travel routes, on ski runs, and at camping sites which then become point sources of eroded sediments. In general, these anthropogenic impacts do not produce erosion by themselves, rather they accelerate natural processes or allow their introduction by changing soil, vegetation, and drainage conditions. Further, they greatly augment the variability in erosion rates and so increase the difficulty of defining trends and changes in

activity.

GEOMORPHIC ACTIVITY IN HIGH MOUNTAINS

Three studies of contemporary activity in high mountain catchments are summarized in Figure 7 (Jiickli, 1956; Rapp, 1960; Caine, 1976). These results clearly differ, reflecting contrasts in catchment size across three orders of magnitude, climate, and geologic structure, and lith-

ology. Despite these contrasts and their influence on estimated levels of activity, some important common features are evident in Figure 7 and worth emphasizing for they may be common to many high mountain areas. For the present, only the average estimates shown in Figure 7 are used and questions of any temporal variability associated with them are ignored.

In all three areas, two components dominate in the geomorphic mass fluxes. First, there is the coarse debris system involving internal transfers of large clastic material by rockfall, avalanches, and debris flows which accounts for between 10 and 60 percent of all the geomorphic work done in the three catchments (Table 2). Contrasts between the three field areas are inversely related to catchment size and relative relief, most likely through the proportion of the total area in cliffs and taluses. Second, the influence of solute transport is almost equivalent to this (from 12 to 50


(a) The Upper Rhine Catchment

Sediment Morphologic Sediment Fluxes System Units

Glacierized Glacial Glacial Valleys Transport

Sa (62.8)

Coarse I Snow

Debris Steep Rockfall Avalanches Mudflows

Debris Steep (554.2) (104-6) (70-35) Systems. Bedrock I A

Slopes 8 Talus Creep Talus / Rock Glacier Flow

(3.0)

f, r /'

Fine Waste I Sediment Mantled I Solifluction and

System Slopes. / Soil Creep 4

I (53.5)

I I

Fluvial Stream Fluvial

8 Channels; Transport a Solute Transport Geochemical Valley Deposition (2781) (3386)

Systems Floors-

(86

Lake Sedimentation Lakes,

(10412)

(b.) Karkevagge, Scandinavia (C) Williams Lake Basin Rocky Mountains

Sediment Morphologic Sediment Fluxes Sediment Morphologic Sediment Fluxes System Units System Units

Glacierized Glacial Glacierized Glacial

Glacial Valleys Transport Glacial Volleys Transport (0.0)

Coarse Snow Coarse Snow Debris Steep Rockafoll Avalanches Mudflows Debris Steep Rockfall Avalanches Mudflows

Systems Bedrock (13.0) (14.6) (64.25) Systems Bedrock (4.1) (0.04) (11.2)

Slopes a Trace Slopes 8 Tolus Talus Creep Talus Talus Creep (1.8) 1 (00.0)

Fine Waste Soluction and Fine Waste Solifluction and Sediment Mantled Soil Creep I Sediment Mantled Soil Creep System Slopes. (3.53 I System Slopes. (339) I7

Slope Wash Slope Wash (00.0) (4-54)

I I /

Fluvial Stream Fluvial Stream /

8 Channels; Fluvial Sediments Solute Transport Channels Solute Transport

Geochemical Volley (not studied) (91.0) Geochemical Volley Lake Sedimentation (3 24)

Systems Floors; - Systems Floors;

Fans 8 "

Fansa

. =, Lakes. Lakes.

FIGURE 7. Sediment fluxes in three high mountain areas. a) the Upper Rhine Basin (Jiickli, 1956); b) Karkevagge, Northern Scandi- navia (Rapp, 1960); c) Williams Lake Basin, Colorado (Caine, 1976). All fluxes are based on vertical transport (106 J/km2/yr).


TABLE 2 Sediment fluxes in three high mountain basins

Catchment Upper Rhine Karkevagge Williams Lake

Area (km2) 4307 15 0.98 Relief (m) 2800 930 275 Coarse debris and bedrock slopes 729.2 (4.2%) 15.7 (58.4%) 93.65 (49.8%)

Soil and fine sediment mantled slopes 53.5 (0.3%) 7.93 (29.5%) 3.53 (1.9%)

Channel transport and lake sedimentation 13798 (79.5%) Not reported Not reported

Solute flux (output) 2781 (16.0%) 3.24 (12.1%) 91.0 (48.3%)

Total 17362 26.87 188.18 Source Jickli (1956) Rapp (1960) Caine (1976)

Units: 106 J/km2/yr.

percent of the work) and is related directly to catchment size. The area control on the geochemical system derives from many sources: the residence times of water within

the catchments; the biomass associated with the lower elevations of large catchments; the thickness and extent of waste mantles; variations in lithology; and the importance of anthropogenic influences all increase with catchment size. In the upper Rhine basin, Jiickli's records suggest that most of the geomorphic work (80 percent) is done by the fluvial transport and deposition of clastic sediments. Al-

though this is not estimated for the smaller catchments

(Table 2), it is unlikely that fluvial processes have an

equivalent significance in most high alpine areas that are not presently glacierized (Caine, 1974).

The summaries of Figure 7 and Table 2 also suggest the relative insignificance in the total sediment budget of alpine areas of some components which have received much attention previously. Talus shift, solifluction, soil creep, and other processes of slow mass wasting account for less than 15 percent of the geomorphic work done in all three areas and their relative importance decreases as the basin size increases. Furthermore, except at the largest spatial scale, erosion and transport through the fluvial channel appears slight, although difficult to evaluate, perhaps an indica- tion of the lack of coupling between hillslope systems (especially that of the cliff-talus) and the fluvial system in high mountain areas. This does not minimize the importance of these components in the landscape, nor their significance in catastrophic slope failure, flooding, and other hazards.

CONCLUSION

This review suggests that there are sufficient common characteristics in past landscape evolution, in landform associations, and in present erosional activity in mountain areas for mountain geomorphology to be considered a

"regional" emphasis within geomorphology. The recogni- tion of such common characteristics should not be allowed to mask the variations and contrasts within and between

high mountain areas, which remain a basic problem in much research. Nevertheless, general statements are more useful and needed than ideographic or "unique" cases.

As a subset of modern geomorphology, mountain geomorphology confronts one overriding problem: that of link-

ing process and form in a meaningful way (Thornes, 1983). In high mountain areas, this need is made more serious

by the significance of catastrophic events in landscape development and by the fact that global environmental

changes may occur on a shorter time-scale than the relaxa- tion times and "characteristic form times" (Thornes, 1983)

of mountain landforms. A further need is that of identify- ing anthropogenic influences, both intended and inad- vertent, and the ways in which they may be propagated through the mountain system or into lower environments. This requires identification of thresholds within the geomorphic system and of landscape sensitivity. Both these are important if geomorphology is to be useful in

prediction. The main significance of mountain geomorphology in

an applied sense lies in hazard assessment, impact evaluation, and land-use planning. In all these, it is important to recognize the common nature of mountain geomorphology. This is not to suggest that simplistic solutions to problems based on generalizations are likely to have much success. Nevertheless, general characteristics do serve to define broad problems and offer initial approximations to solutions.

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