PR OB LE M S OF RE LIE F PL ANA TION
PROBLEMS .F RELIEF
PLANATION
AKADÉMIAI KIADÚ, BUDAPEST
P R O B L E M S OF
R E L I E F P L A N A T I O N
Studies in Geography in Hungary, 8 Edited by M. Pécsi
In this volume problems of planation processes in low mountains and their forelands and the resulting land forms are discussed.
The introductory paper gives infor
mation about the character, dynamics and trends of the recently discovered planation processes in the middle mountains o f the Earth, and the vari
egated complexes of land forms brought about by these. With a view to clearing up terminological confusion, the paper points out contradictory usage anti suggests new solutions.
The Hungarian authors concern them
selves with the hitherto little-known form types of the planation levels in the Hungarian Mountains. They disclose up-to-date notions on the evolution o f these forms and report on the latest methodological develop
ments.
Authors from abroad interpret the climatic conditions controlling plana
tion, provide analysis and model of the processes and forms of the semi- arid zone so conducive to planation, and clarify the evolution of some special forms.
International scholarship calling for terminological clarity will find this book serviceable as a foundation of principles and methods of recent geo- morphological investigations in Hun
gary. Research workers and teachers in all parts of the world, as well as cartogeographers following this new and practical discipline of physical geography, will be faced here with new ideas and challenges.
A K A D É M I A I K I A D Ó
Publishing House of the Hungarian Academy o f Sciences
B u d a p e s t
PROBLEMS OF RELIEF PLANATI ON
S T U I) I K S i N G E 0 G ISA IMI Y I N H U N GA RY, 8
G eographical R esea rch In s titu te
H ungarian A cad em y of Sciences. B udapest
C hief editor:
M. P É C S I E d ito ria l b o a rd :
Ä. B O R A I, G Y . l i . W K D I . li. S Á R F A L V I a n d J . S Z IL Á R D
PROBLEMS OF RELIEF PLANATION
E d ite d b y
MÁRTÓX PÉCSI
AKADÉMIAI KIADÓ. BUDAPEST 1970
P ro c e ed in g s o f t h e I n te r n a tio n a l S y m p o s iu m , 16th—2 0 1h A pril, 1968, o rg a n iz ed b y th e G e o g ra p h ic a l R e s e a rc h I n s titu te , Hung. A c ad . Sei., u n d e r th e title “ G E O M O R P H O L O G IC A L A N D T E R M IN O L O G IC A L P R O B L E M S O F M O U N T A IN S A N D T H E I R F O R E L A N D S , T H E P E D IM E N T S ”
T r a n s la te d by B . B a lk a y
T r a n s la tio n re v is e d l>y P h ilip E . U ren
(C) A k ad ém iai K ia d ó , B u d a p e s t 1 9 /0 P rin te d in H u n g a r y
AUTHOR LIST
B e rn ard D U M A S
I n s titu te o f G e o g rap h y — U n iv e rsity o f P a r is — P aris J o h a n n e s F . G E L L E R T
G e o g ra p h ic a l I n s titu te — T ea ch e rs’ T ra in in g College — P o ts d a m Ism ail P a v lo v ic h K A R T A S H O V
I n s titu te o f G eology — A c a d e m y of Sciences, U S S R — M oscow G y ö rg y L O V Á SZ
T r a n s d a n u h ia n S cien tific I n s t i tu t e — H u n g a r ia n A cadem y o f S cien ces — P écs
| J . H o o v e r M A C K IN j
D e p a r tm e n t o f G eological Sciences — U n iv e r s ity o f T exas a t A u s tin — A u s tin H o rs t M E N S C H IN G
I n s titu te o f G e o g rap h y — T ec h n ical U n iv e r s ity — H a n n o v e r M árto n P É C S I
G e o g rap h ic al R esearch I n s t i t u t e — H u n g a r ia n A cadem y o f S cien ces — B u d a p e s t Z o ltá n P IN C Z É S
I n s titu te o f G e o g rap h y — K o s su th L ajo s U n iv e rs ity of S cien ces — D ebrecen M ihail V la d im iro v ic h P IO T R O V S K Y
D e p a r tm e n t o f G eology — S ta te U n iv e rsity o f Moscow — M oscow E rh a rd R O S E N K R A N Z
D e p a rtm e n t o f G e o g ra p h y a n d Geology — F rie d ric h S c h ille r U n iv e rsity o f S ciences
— J e n a A ndrás S Z É K E L Y
I n s t i tu t e o f G e o g rap h y — E ö tv ö s L o rán d U n iv e rs ity o f S cien ces — B u d a p e s t J e n ő S Z IL Á R D
G e o g rap h ic al R esearch I n s t i tu t e — H u n g a r ia n A cadem y o f S cien ces — B u d a p e s t
CONTENTS
P re fa c e 9
In tro d u c tio n . F u n d a m e n ta l p ro b lem s o f re lief p la n a tio n I f P éc si, M. an d S z ilá rd , J . : P la n a te d s u rfa c e s: p rin c ip a l p ro b le m s of research a n d te rm in o lo g y 13 P éc si, M .: S urfaces o f p la n a tio n in t h e H u n g a ria n M o u n ta in s a n d t h e ir re le v a n c e to
p e d im e n t a t ion 29
S z é k ely , A.: L an d fo rm s o f the M á tra M o u n ta in s and th e ir e v o lu tio n w ith sp e c ia l re g a rd
to surfaces o f p la n a tio n á I
P in c z é s, Z.: P la n a te d su rfa ce s a n d p e d im e n ts of th e B ü k k M o u n ta in s 55 L o v á s z , G y.: S u rfaces o f p la n a tio n in th e M ecsek M o u n ta in s (>5 M ensch ing, II.: P la n a tio n in arid s u b tr o p ic a n d tr o p ic regions 73 M ack in J . II. : O rig in of p ed im e n ts in th e W e s te rn U n ite d S ta te s 85 G e lle rt, J . F . : C lim a to m o rp h o lo g y a n d p a la e o c lim a te s o f th e C e n tra l E u ro p e a n T e rtia ry 1 0/
D u m a s, B.: T he o rig in o f glacis M3
P io tr o v s k y , M. V .: T h e p ro b lem o f p e d im e n ts a n d m o rp h o te e to n ic s 119 K a r ta s h o v , I. P .: V a lle y p e d im e n ts o r d e n u d e d te rra c e s (te rra so u v a ls ) ? 127 llo s e n k ra n z , E .: P e d im e n ts on th e n o r th e a s te r n b o rd e r o f th e T h u rin g ia n F o rest 133
B ib lio g ra p h y 137
PREFACE
The present volum e, e ig h th in the series “ Studies in G eography in H u n g a ry ” , presented by th e Geographical Research Institute, H ungarian A cadem y of Sciences, has for its s u b je e t one of th e m ore im p o rta n t problem s of m odern geom orphology which concerns the processes of p la n a tio n in low m ountains and th e ir forelands, as well as th e lan d forms re su ltin g therefrom . In this book em inent experts on th e subject from H ungary a n d abroad discuss th e relev an t theoretical achievem ents m o st w orthy of a tte n tio n . These c o n tri
butions were originally read during th e Sym posium of 16-20 April, 1968, organized by the G eographical R esearch In stitu te.
The in tro d u cto ry essay contains inform ation about th e ch aracter, dynam ics an d tren d s of some re c e n tly discovered planation processes which are ac tiv e in th e m iddle m o u n tain regions of th e E a rth , as well as a b o u t the v arie g ated com plexes of land form s brought a b o u t by these processes. In ad d itio n , d etailed analysis is given concerning th e present-day sta n d in g of th e diverse research trends in th is dom ain of them es. P articu lar in te re s t m ay be a tta c h e d to th e p aper inasm uch as it exposes th e contradictory usage of various term s, providing a t th e sam e tim e some propositions with a view to clearing u p the term inological confusion.
C ontributions by H u n g a rian au th o rs concern them selves w ith the h ith e rto little know n form ty p e s of the levels of planation in th e H ungarian M oun
tains in terp re tin g th e ir evolution according to the la te s t m ethodological de
velopm ents.
C ontributions by a u th o rs from ab ro a d sim ilarly expound special and general problem s of p lanation. These include a novel in te rp re ta tio n of th e clim atic conditions controlling plan atio n , a profound analysis and m odel of the processes and form s of the sem iarid zone so conducive to p lan atio n , as well as th e action of som e peculiar processes and th e evolution of certain special forms.
F inally, this book is a re p resen ta tiv e selection of th e results of H u n g a rian geom orphological research — e ith e r unpublished so far, or published in a form difficult to o b ta in for scientists abroad — show ing the in tern a tio n al stan d in g an d th e m odern m ethods of this ac tiv ity . Also discussing and e v a lu a tin g the m ain problem s of in te rn a tio n a l research an d urging te rm i
nological clarity, th is book may hopefully serve as a fo u n d a tio n in th e p rin ciples an d m ethods of th e subject for both research w orkers and teach ers.
C artogeographers of such interest in physical geography also find here new ideas an d challenges.
M . Pécsi and J . Szilárd i)
INTRODUCTION
FU N D A M EN TA L PR O B LEM S OF R E L IE F PLA N A TIO N
The great form s of llie E a r t h ’s relief are sculptured by endogenic agencies.
Their action, altern atin g in tim e and space, augm ents th e relief energy of th e surface. As a consequence, g ra v ity compels th e exogenic agencies to tr a n s port and deposit more w aste over certain periods of tim e a n d certain areas th a n over o th ers. The resu lts of th e exogenic processes are fu rth e r modified zonally and locally by th e p a rtic u la r ecologic conditions e x istin g a t the place an d time u n d e r consideration; it is this in tera ctio n th a t d eterm in es the n a tu re of th e p lan atio n of th e relief.
The unceasing bu t v a ry in g action of endogenic agencies brings a b o u t a differentiation of the re p e a te d ly re ju v e n ated relief. The p la n a tio n w rought by sim ilarly unceasing exogenic agencies is, on th e other h an d , controlled by th e a lte rn a tio n in tim e and space of th e in te n sity of active g ra v ity (i.e. slope angles) an d of th e given ecologic conditions. Locally an d periodically, th e exogenic agencies m ay also brin g about a dissection of th e relief, lien ee, th e actio n of th e exogenic processes is in v aria b ly subject to outside control ra th e r th a n being teleologic in n atu re. On th e other h a n d , th e process of relief plan atio n is not s tric tly periodic, w ith a repetition of identical s ta te s ; there is m erely a rhythm ic recurrence of sim ilar states in th e course of unceas
ing change.
The p lan ate d surfaces recognized in various regions a re highly v aried . Fhe in te rp re ta tio n of th e ir origin has long been controversial an d has been a focal point, as it were, of m an y fu n d a m e n tal ideas an d principles of relief evolution, an d of geom orphology in general. On the o th e r h a n d , it is also connected ra th e r in tim ate ly w ith a nu m b er of problems of a m ore practical n a tu re , such as th e occurrence of shallow m ineral deposits in deeply eroded regions, an d of residual ores—b au x ite, m anganese—in co rrelate deposits, etc.
I t m ay fu rth e r serve as a basis for a “ co n tin en tal s tra tig ra p h y ” of regions where erosion has been going on u n in te rru p te d for long sp an s of geologic lim e. A corollary of this idea is, for exam ple, th e m ethod of determ ining th e age of th e relief during th e geom orphological m apping of m ountainous regions.
The topic includes in its theoretical aspect several problem s of a general an d fu n d a m e n tal nature.
(1) P la n a te d surfaces are form ed—in gen eral—by th e w ell-defined in te r actions of exogenic and endogenic agencies, w ith the exogenic agencies d o m i
nating (Chemekov, 1964; Filosofov, 1964; Klim aszewski, 1965). It is no t.
however, clear from this definition ju st how th e agencies m entioned b rin g ab o u t th e scu lp tu re of p la n a te d surfaces. Is planation, or th e stepw ise system
of plan ated surfaces, a re s u lt of a co n tin u ed or stepw ise uplifting, or of th e stab ility , or of th e g ra d u a l sinking of th e te rre stria l c ru s t?
(2) I t was usual, in e a rlie r tim es, to em phasize th e ro le of linear erosion am ong the ex tern al agencies of p lan atio n ; lately , a lth o u g h , th e differentiated analysis of th e specific com binations of exogenic agencies in individual cli
m atic zones has becom e th e rule. O ur u n d e rsta n d in g of th e effects of clim ate upon relief is, how ever, fa r from unequivocal. I t is only clear, th a t in ce rtain clim atic zones e x tern al agencies are especially effective an d m ay produce p e
culiar land forms.
(3) Still profoundly p ro b lem a tic is th e in te rp re ta tio n of the origin of peneplain steps an d p e d im e n t steps. A re th ey the re su lt of the stru c tu ra l dissection of a previous contiguous su rface; are th e y p la n a te d surfaces of different age, or the a u to d y n a m ic results of an u n in te rru p te d process of pla- n atio n ? [Some ascribe th e developm ent of stepped, tru n c a te d surfaces to a continuous stru c tu ra l u p liftin g (Penck, 1924); others a ttr ib u te this to con
tinuous exogenic processes, e.g. continuous stream erosion (K ádár, 1966);
still others re la te it to geophysical factors (Geyl, I960).]
(4) The influence of lith o lo g y upon th e planation of relief is not in general considered decisive, e x c e p t in some local cases. Still, lithologic v arie ty m ay resu lt in deviations fro m ty p ic a l form s a n d this is, in som e m easure, still open to fu rth e r research.
(5) F or th e in te rp re ta tio n of the low ering of slopes, th re e com prehensive hypotheses have been developed:
(a) th e rounding a n d overall low ering of divides b y non-parallel slope recession (D avis, 1922; P h ilippson, 1931; B irot, 1949; e tc.);
(h) parallel recession of slopes (P enck, 1924; L eh m an n , 1933; B akkor, 1956; etc.);
(c) a com bination of th e above tw o has also been considered (Bűdéi, 1957b, 1965; C otton, 1961; etc.).
(6) All in all, th e in te re sts of research, a n d of in te rn a tio n a l scientific u n d e r
stan d in g an d cooperation, in b o th principle an d practice, m ak e it indispensable to a tta in clarity of term in o lo g y , to id en tify synonym s a n d to define v a ri
a n ts rigorously. The lack of such definitions has caused us no little inconven
ience.
M . Pécsi
12
PLANATED SURFACES: PRINCIPAL PROBLEMS OF RESEARCH AND TERMINOLOGY1
*>y
\[. P É C S I a n d J . S Z I L Á R D
I. T H E O R IE S OF R E L IE F PLA N A TIO N
I. T R U N C A T E D , P L A N A T E D S U R F A C E S (R U M P F F L Ä C H E N )
The genetic an d topog rap h ic in te rp re ta tio n of the concept is ra th e r diverse in lite ra tu re . T aking into consideration all definitions, b o th narrow an d b ro a d , it emerges th a t tru n c a te d , planated surfaces are considered plane surfaces of considerable e x te n t an d low relief energy, usually in m ountains, o v er a stable or g e n tly rising base. They are s c u lp tu re d by th e processes of d e s tru c tion, and b y a well-defined equilibrium of uplifting an d degradation.
W hile som e auth o rs consider tru n c a te d surfaces to be th e re su lts of sculpture by a single specific agency of d e stru c tio n , others consider th em poly- genetic; th a t is to say, th e y result from th e in teraction of several agencies, w ith th e intensities of th e co n trib u tin g agencies v arying in tim e an d space (M eshcheryakov, 1964; K lein, 1959a; P enck, 1924; etc.). A ccording to th e views of som e, tru n c a te d surfaces are polygenetic also in space. Their com plex of forms includes not only surfaces of d eg rad atio n , b u t also of accum ulation and accum ulo-denudation, closely related to th e surfaces of pure d e n u d a tio n (M eshcheryakov, 1964). Pécsi (1967) coined th e term “ surface of d e p la n a tio n ” for th e form er and “ surface of a p p la n a tio n ” for th e la tte r.
(a) A brasional p lan ated surface
The earliest in te rp re ta tio n of p lan ated surfaces was given by the B ritish scientist A. C. R am say (1846). The idea underlying his in te rp re ta tio n was m arine erosion, and th e th e o ry of p en e p lan atio n by ab rasio n was long p a r a m ount in E ngland. In G erm any, it found an exponent in th e person of von R ichthofen. U p to the final q u a rte r of th e last century it played a d o m in a t
ing role in th e in te rp re ta tio n of p lan ate d surfaces fringing recent an d ancient seas.
There are clearly qu ite broad terraces of abrasion, or step p ed system s of this kind, along to d a y ’s seashores, a n d fossil terraces of abrasion can be recognized also along th e shores of an c ie n t seas. The m a jo rity of researchers, however, re je ct th e possibility of ex ten siv e abrasional planes of su b c o n ti
n ental size. C onsequently, th e term “a b ra d e d peneplain” should be rejected and th e term s “ m arine te rra c e s” , “ shore p latfo rm s” or “ m arine h alfp la n es”
should be in tro d u ced in its stead. 1
1 I n th e p r e s e n t p a p e r th e t e r m “ p la n a te d s u r f a c e ” is u sed in a v e r y g e n era l sen se fo r all k in d s o f d ep la n a ted surfaces.
13
(b) P eneplain (E ndrum pf)
This te rm w as coined in Í899 b y W . M. D avis in reference to extensive, alm ost plane surfaces, scu lp tu red b y su b ae rial processes, such as stre a m erosion, a n d developed in various h u m id regions a t th e base level of erosion in the p e n u ltim a te stage of relief low ering. The D avisian peneplain is due to a lowering of divides over periods of prolonged tectonic rest.
This concept has come to be w idely ac cep ted an d has in th e process gained a context m u ch b ro a d er th a n th a t originally intended b y Davis. The n u m b er of peneplains described b y researchers from all over th e w orld has become so large t h a t — as recorded by W . D. T h o rn b u rv (1954)— Davis him self felt com pelled to p re ach re stra in t to his followers.
The m ain p o in t of co n tro v ersy ab o u t th is th eo ry was w hether it justified the assu m p tio n of quiet periods during w hich den u d atio n a tta in e d th e p en u l
tim a te stage in th e cycle of evolution. T he cyclicity of relief evolution has also been co n teste d , and as th e peneplain is a necessary consequence of th e D avisian th e o ry of cycles, re fu tin g the possibility of cycles is equivalent to refuting th e peneplain concept.2
M odifying D a v is’s original th eo ry , several auth o rs cam e to the conclusion th a t p en e p la n atio n can also ta k e place d u rin g a slow a n d co n stan t uplifting, as long as th e ra te of rise is lower th a n th e r a te of d egradation. D avis’s p o ly cyclic in te rp re ta tio n 3 of step p ed peneplains was also w idely accepted witli more or less extensive m odifications.
Even D a v is’s A m erican followers a c cep ted his th eo ry of p eneplanation w ith m odifications of g re a te r o r less significance. According to W. D. T horn- b ury (1954), to preserve th e original co n c ep t of Davis m eans to apply th e term peneplain to the sm oothed surfaces on divides developed tow ards the end of th e cycle of erosion p a rtia lly as a re su lt of lateral p lan atio n by stream s, and p a rtia lly as a result of m ass w asting on th e slopes. This is a considerable restriction of th e original D avisian idea. Surfaces sim ilar to peneplains bu t sculptured b y o th er agencies, or u n d er different conditions, should be given o th er nam es (B ulla, 1954a; T h o rn b u ry , 1954; etc.). H ow ever, a t th e tim e th e peneplain con cep t cam e into existence th e necessary d istin ctiv e criteria and names were as y e t lacking.
The opinion t h a t u n d er a te m p e ra te clim ate processes of erosion will never bring ab o u t a full sm oothing or p en e p la n atio n is now gaining ground. Such
2 In D a v is ’s in te r p r e ta tio n , th e cycle o f e ro sio n is re lie f e v o lu tio n r e tu r n in g in v a r ia b ly to th e sam e in itia l s t a te ; i t is c o m p o sed of a lo n g p e rio d o f ero sio n a n d p la n a tio n a n d a r e ju v e n a tio n of th e re lie f b y a s u d d e n u p liftin g . T h e la c k o f success of t h e D a v isian th e o r y w as
— acco rd in g to g e o m o rp h o lo g ica l l ite r a tu r e — d u e p rim a r ily to its a n ti-d ia le c tic i n te r p r e t a tio n of relief e v o lu tio n as a cyclic process.
3 D avis a s s u m e d p erio d s o f lo n g te c to n ic r e s t in t h e e v o lu tio n of a m o u n ta in ; th e e v o lu tio n d u rin g su ch a p e rio d p ro d u c es a p e n e p la in in t h e p e n u ltim a te sta g e o f th e cycle o f ero sio n , w hich s u b s e q u e n tly u n d e rg o es r e p e a te d u p liftin g . O n th e m o u n ta in m a rg in , a t th e b aselevel o f erosion, t r u n c a te d su rfa ce s, p a r tia l p e n ep lain s co m e in to ex isten ce. W h e re v e r a n d w h e n e v e r th e p eriods o f te c to n ic re s t w ere n o t lo n g e n o u g h for t h e process o f p e n e p la n a tio n to c o m p letely w e ar a w a y th e re lief fo rm ed d u rin g th e p re v io u s cycle a n d su b s e q u e n tly u p lifte d , th e re occur, a c c o rd in g to D a v is, r e m n a n ts o f o ld e r p e n e p la in s a t h ig h e r «altitudes, in a s t e p w ise a rra n g e m e n t.
surfaces conserved in a te m p e ra te area a re vestiges of a preceding period of tropical clim ate. Still, even in the face of th ese arg u m en ts, th ere are som e who hold t h a t peneplains can develop in h u m id tem p erate areas, for exam ple, under a fo rest cover (Baulig, 1956), or as a result of fluvial erosion in general (B ulla, 1954b).
Several S ov iet authors represent th e view th a t in m o untainous regions the rh y th m ic repetition of tectonic m ovem ents precludes th e prolongation of sm oothing processes u p to th e last stag e of th e cycle of erosion, th a t is to say th a t ty p ic a l peneplains can nowhere develop. These sm oothed, p lan ate d surfaces in th e interm ed iary phase of ev o lu tio n they call “ den u d atio n al p la n ated su rfaces” as distinct from peneplains (D um itrashko, 1954; C hem ekov.
1964; S h chukin, 1948; an d others).
A ccording to Yu. F. Chem ekov (1964), “ denudational p la n a te d su rfaces’
develop in th e phases of re st in the general process of arch in g . He considers I he difference in forms b etw een prim ary a n d final peneplains to be much less th a n a d v o c ated by Penck. H e holds th e tw o sets of form s to be genetically identical. In his opinion, th e difference lies in the fa ct t h a t whereas final peneplains are th e result of a very long process of sm oothing, th e re p eated phases in a n orogenically m obile zone b rin g ab o u t only a p a rtia l sm oothness which is d elay e d in an in term ed iate phase. In this sense C hem ekov’s line of th o u g h t is close to D avis’s polycyclic in te rp re ta tio n of ste p p e d peneplains.4 Also according to Chem ekov, the longer th e duration of relative tecto n ic re st, th e m ore extensive a n d profound th e sculpture of a d en u d atio n al p en e
plain. H ence, he considers “ d enudational p la n a te d surfaces” to be results of th e sam e dow nw ard relief evolution as peneplains proper, th e processes a t th e ir origin being genetically identical. The difference is in d ep th and e x te n t, depending o n th e d u ratio n of sculpture. l i e considers peneplains and pedi plains to be th e final surfaces of “ d en u d a tio n a l p lan atio n ” .
A ccording to Chemekov, th e d en u d a tio n a l planated surfaces m entioned ab o v e can develop under various hum id clim ates (w arm tem p erate, s u b tropical or tro p ical). To su p p o rt this s ta te m e n t he produces a great deal of analytical evidence.
(c) E qual p eak heights
According to th e D avisian th eo ry of cycles, the levels defined by peaks of equal height, an d by the to p s an d stepped flanks of divides, are rem nants of peneplains form ed at various baselevels of erosion during m any successive
4 A cco rd in g to C hem ekov, c o n d itio n s for th e d e v e lo p m e n t of a s te p p e d , p la n a te d s u rfa c e a re m o st fa v o u ra b le in th e b o rd e rz o n e betw een m o u n ta in s a n d basins. H e d istin g u ish e d zo n es o f ex clu siv e u p lif tin g a n d zones o f ex clusive su b s id e n c e . B etw een th e tw o , th e re is a z o n e o f zero g ra d ie n t w h ic h is e sse n tia lly t h e th e a tr e of t h e p ro c esses o f d e p la n a tio n . O n th e r e p e titio n o f te c to n ic u p lif tin g , t h a t p a r t o f t h e p la n a te d s u rfa c e form ed in th e z o n e of zero g r a d ie n t w h ich is a d ja c e n t to th e foot o f t h e m o u n ta in b eco m es p a r t of th e z o n e o f u p liftin g , a re lic , o n e o f th e s te p s o f th e ste p p ed t r u n c a te d su rface. S u b s e q u e n tly a n e w p h a s e of sm o o th in g se ts in a t th e le v e l o f zero g ra d ie n t, in th e fo relan d o f t h e form er, u p lif te d su rface.
15
cycles. I t w as in opposition to an d in re fu ta tio n of th is theory, and of tin- cycle th eo ry in general, t h a t A. P enck developed his ow n theory of equal peak heights. I n his opinion, eq u al peak h eig h ts will result also from th e sim ple uplifting of a m o u n tain . The valley slopes of stream s, incised to ap p roxim ately equal depths in to th e ho d y of th e m o u n tain , intersect th e interfluvial p la te a u x a t about eq u al heights w ith o u t actu ally proving the ex isten ce of an ancient peneplain.
A. Penck (1919) fu rth e r considered it definite th a t erosion has an u p p e r lim it, a rriv ed a t th ro u g h th e in te ra c tio n of th e given exogenic and e n d o genic agencies, and above w hich th e relief will not em erge. His “G ipfelflur th eo ry ” , how ever, was accepted only fo r th e in te rp re ta tio n of th e equal peak heights of alp in o ty p e m o u n tain s: its v alid ity for low m ountains and tru n ca ted surfaces was w idely doubted. In o u r experience, on the o th er h a n d . A. P enck’s e x p la n a tio n of divides of eq u a l height m erits some a tte n tio n in the analysis of low -m ountain regions as well.
( d) The p rim a ry peneplain (P rim ärru m p f) th eo ry and th e th e o ry of piedm ont benchlands or steps (P ied m o n ttrep p en )
To replace th e D avisian polycyclic ex p lan a tio n of ste p p e d planated s u r
faces, an d also as a re fu ta tio n of th e an ti-d ialec tic th eo ry of cycles, W . P enck 1924) gave an “ au to d y n a m ic ” in te rp re ta tio n of stepped planated su rfaces.5 The basis of his hypothesis is th e assu m p tio n of an arch in g , slow a t firs t.
b u t which accelerates an d ex ten d s in tim e . According to W . Penck, an e q u i
librium surface, a so-called P rim ärru m p f, will th en develop over th e slowly rising region, its rise being com pensated for by erosion. T he evolution of th e relief is e x a c tly opposite to t h a t assum ed b y Davis. On th e rising piedm ont surfaces, th e slopes are n o t senile, b u t regress parallel to them selves in th e direction of th e valley flanks. H ence, th e P enckian s te p p e d surfaces are not decaying fossil forms, an d th e p rim ary planes (P rim ärrüm pfe) are no t in th e
process of evolution.
A lthough th e most em p h atic point of P e n c k ’s P ie d m o n ttre p p e h ypothesis was fully re je c te d b y su b seq u e n t criticism , his th o u g h t-p ro v o k in g th eo ry g av e an incentive to fu rth e r research.
Several a u th o rs h av e m ade a tte m p ts a t fu rth e r developing and m odifying P enck’s ideas: H. S p reitzer (1951), for exam ple, has a ttrib u te d p ied m o n t steps to a periodic arching, in te rru p te d by phases of rest, an d extending over
5 In th e P e n c k ia n in te r p r e ta tio n o f ste p p e d R u m p fflä c h e n , th e i n itia l su rfa ce is th e “ P r i m ä r r u m p f” , b u t i t m a y b e also th e D a v is ia n p e n e p la in , t h e “ E n d r u m p f ” , “ E n d p e n e p la n e ” . A s a re s u lt o f a rc h in g , a p ro cess e x te n d in g in a re a a n d a cc e le ra tin g in tim e , th e riv e r g ra d e s a re b ro k e n a n d e m p h a s iz e d a t t h e m a rg in s of th e a r e a b e in g u p lifte d . V a lle y s incise th e m s e lv e s , a n d th e v a lle y flan k s g ra d u a lly r e t r e a t a n d b r o a d e n a t th e e x p e n s e o f th e h ig h er s u rfa c e . T he b ro a d e n in g a r c h e m b ra ce s a w id e r a n d w id e r a r e a a n d th u s a n e v e r in creasin g n u m b e r o f y o u n g e r s te p su rfa c e s is c o n n e c te d to th e m o st h ig h ly ele v ate d c e n tr a l a rc h . I t is th is s y s te m o f stepw ise r e p e a te d tr u n c a te d , p la n a te d su rfa c e s t h a t w as called “ P ie d m o n ttr e p p e n ” b y Penck.
1(i
an ever broadening area, ra th e r th a n lo a p ro tra cted and c o n s ta n t-ra te u p lift
ing;6
The P en ck ian hypothesis was also a d o p te d w ith profound m odifications b y several S oviet scientists (Gerasim ov, M esheheryakov, P io tro v sk y ). A. P. Ded- kov (1965) has pointed o u t th a t p lan ate d surfaces occurring a t various a l t i tudes in th e m ountains are th e results of a relief evolution continuing u n in te r
ru p ted since th e E a rly T ertia ry period.
A lthough W. Penck, in m o tiv atin g th e evolution of his R um pfflächen, pointed o u t th e peculiar role of w eathering, he a ttrib u te d p la n a tio n —u n d e r I he assum ed tectonic conditions—to norm al fluvial erosion. 1 lis teachings were m odified also in this respect by H. S p reitzer (1951). According to this la tte r a u th o r, th e evolution of piedm ont ste p s —and th a t is to say of p lan ate d surfaces— is re stric te d to h o t, a lte rn a te ly h u m id and d ry clim ates, w ith co n siderable slopew ash c o n trib u tin g to stre a m erosion. He considers the p ie d m ont steps of m oderately hum id regions as decaying fossil forms.
T h e c o n c e p t o f p ie d m o n t s te p s is re je c te d b y so m e , to g e th e r w ith t h e o rig in al P e n c k ia n idea as a w h o le, w h ereas o th e rs u se it in a m o re o r less m odified form , o f te n w ith o u t p o in tin g o u t a n y differen ces from th e o rig in a l P e n c k ia n d e fin itio n . A fu rth e r f r e q u e n tly arisin g p ro b le m of te rm in o lo g y is th e in d is c rim in a te use o f th e te r m s “ erosional s u r f a c e ” , “ d e n u d a tio n a l tr u n c a te d s u rfa c e ” , “ level o f e ro s io n ” , “ level o f d e n u d a tio n ” , “ p a r tia l p e n e p la in ” a n d o th e r s , for th e s te p p e d su rfaces of p la n a tio n alo n g th e m a rg in s a n d also in t h e p rin c ip a l m o u n ta in m asses. A u n ifo rm te rm in o lo g y b a se d o n a c o m p re h en s iv e a g ree m e n t c o n c e rn in g th e s e s te p p e d su rfaces of d e p la n a tio n is m u ch to be d e sire d .7
(c) P ediplain
The concept was proposed by J . M. M uxson and G. H. A nderson (1935) fo r surfaces resulting from plan atio n by extensive destruction a n d from the in te r grow th of pedim ents in arid or sem iarid regions. L ate r on. A. D. H ow ard (1942) proposed th e te rm pediplain for th e sam e concept. In his opinion, I lie p lan ate d surfaces called “ F la tto p ” a n d “ R ocky M o u n tain ” in the R ockies for exam ple, are pediplains ra th e r th a n tr u e peneplains. A sim ilar view was expressed b y J . H. M ackin (1947) in bis in te rp re ta tio n of th e “ Subsum m it"
level of the Bighorn M ountains.
Pediplains have usually been deduced from pedim ents. 11 was in eonnec- tion w ith these forms th a t Am erican geologists and geom orphologists first came to a ttrib u te a decisive role to clim atic factors. T hey re in te rp rete d as
G II. S p re itz e r (1951) d istin g u ish e d tw o v a r ia n ts o f p ie d m o n t step s s c u lp tu re d b y slo p e w a sh an d ch em ical w e a th e rin g :
(a) N a rro w ledge-like p ie d m o n t step s o n u p lifte d b lo ck s, form ed a t t h e o p en in g s of v a lle y s issuing from t h e m o u n ta in s in p e rio d s o f r e la tiv e te c to n ic re st;
(b) P ie d m o n t ste p s s c u lp tu re d in th e e p iso d es o f r e s t of b r o a d e n in g a n d a c c e le ra tin g arch in g . I t is th e s e l a t t e r t h a t a re ty p ic a l p ie d m o n t s te p s : also, th e y a re m o re w id e sp re a d th a n th e p re c e d in g ones, w h ich a re re stric te d to fu n n e l-s h a p e d v a lle y m o u th s on the m o u n ta in m arg in .
7 Since th e step w ise a rra n g e m e n t o f “ p la n a te d s u rfa c e s ” occurs n o t o n ly in th e m a rg in a l
— p ie d m o n t— zo n e o f th e m o u n ta in s , b u t also in t h e i r in te rio r, we p ro p o s e for th em th e n a m e pinnated m o u n ta in step (G e b irg s ru m p ftre p p e).
17
pediplains a n u m b e r of ex ten siv e p la n a te d surfaces h eld to be peneplains by Davis. L. C. K ing (1962) h as lately expressed the view t h a t p ediplanation is the m ost general form of relief sm oothing, su b stitu tin g , as it w ere, th e p ed ip lan atio n concept for th e D avisian peneplain con cep t, in th is w ay.
how ever, K ing (1950, 1962) g av e an u n d u ly broad co n te x t to the te rm p ed i
plain, u n d er w hich h ea d in g he included all th e exten siv e plan ated surfaces of all th e c o n tin en ts as fa r b ac k as th e C retaceous. In K in g ’s opinion p e d i
plains are ty p ic a l of sem iarid tropical zones, b u t m ay also develop a t low er intensities u n d e r m o d era tely hu m id clim atic conditions. He considers th e differences b etw e en form s developed in arid , sem iarid an d m oderately hum id clim atic zones to consist m erely of th e in te n s ity of developm ent.8
The ped ip lain concept has, w ith c e rta in restrictions, b een applied by several au th o rs to th e in te rp re ta tio n of vario u s surfaces (G rachev, 1962; D edkov, 1965; B igarella, 1965; C o tto n , 1955; Pécsi, 1966; and m an y others). A ccording to M. D erruau (1956), how ever, pediplains m ay develop under tro p ica l cli
m ates only, w hereas A. C ailleux re stric ts th e clim atic co n n o tatio n of p e d i
plain d evelopm ent to th e sem iarid zone. H ence, th e pediplains outside th e sem iarid zones of to d a y w ould all be fossil landscape form s.
A nother op en questio n concerns th e c rite ria of identification for th e p ed i
plain, as a re m n a n t of som e p la n a te d surface outside th e sem iarid zone.
(f) Tropical p la n a te d surfaces
Since th e q u a lita tiv e an d q u a n tita tiv e effects of e x te rn a l agencies in th e existing m orphologic zones of th e E a r th h av e been stu d ied in sufficient d ep th (B ulla, 1954a, b ; B üdel, 1948, 1957a, b, 1965; D resch, 1957a; K a y se r—
O b st, 1949; K re b s, 1933; T ric a rt, 1950, 1961; and o th ers), the view th a i extensive p la n a te d surfaces a re m ost re a d ily formed u n d e r hum id or a lte r n ately hu m id a n d arid tro p ica l clim ates h as become m ore an d more w idely accepted. The in itia to rs of th e th eo ry ex p lain e d th e sm o o th in g of these areas by extensive colloidal a n d subcolloidal w eathering as w ell as by large-scale slopewashing (B ulla, 1954a, b , 1958; B üdel, 1957a, 1965; Louis. 1957, 1961:
Bakkor, 1957a, b ; C otton, 1961). The m echanism of d e n u d a tio n in the a lte r nately arid a n d h u m id tro p ic a l regions (Flächenspülzone) was analyzed in I he greatest d e ta il b y J . B üdel (1957a, 1965), C. A. C o tto n (1961), H. Louis (1957, 1964, 1968), .1. A. M a b b u tt (1961, 1965). Büdel in te rp re te d th e ev o lu tion of tro p ica l p la n a te d surfaces b y developing th e th eo ry of “ dup licate planation su rfa ces” (doppelte E inebnungsflächen).9
8 L. C. K in g r e fu te s th e s e p a r a te e x is te n c e o f h u m id , sem iarid a n d a r id cycles of e v o lu tio n as proposed b y D a v is , since a ll c y clical fo rm s— th o s e o f th e g la c ia te d reg io n s e x c e p te d — a r c fu n d a m e n ta lly id e n tic a l. K in g c o n sid ers p e d ip la n a tio n to be a g e n e ra l p ro cess an d t h e f o r m a t io n of p e d ip la in s t o h a v e t a k e n p la c e s im u lta n e o u s ly a ll o v e r th e w o rld .
9 In th e z o n e o f tro p ic a l slo p e w a sh in g , th e s u rfa c e s a re th ic k ly c o v e re d w ith p r o d u c ts o f w e ath e rin g , u n d e r la in b y a less th o ro u g h ly s m o o th e d b u t still h u m m o c k y re lief of u n w e a th e re d ro c k (e.g. g ra n ite ). T h is d e e p e r in te r f a c e is th e b a s a l f r o n t o f p la n a tio n , sm o o th ed b y w e a th e r ing. D ouble p la n a tio n ta k e s p la c e , o n th e o n e h a n d , b y slopew ash o n th e surface clo ak o f w e a th e rin g p r o d u c ts (S p ü lo b e rflä ch e ) a n d , on th e o t h e r h a n d , b y s u b s u rfa c e w e a th e rin g on t h e deeper in te rfa c e .
IS
B. Bulla (1954a, 1958) em phatically e x ten d e d th e th eo retical area of th e form ation of these tropical p lan ated surfaces to cover th e zone of tro p ica l rain forests, w hereas Biidel (1957a) considered it only p robable th a t such an extension is justified. According to Bulla, p la n a te d surfaces regularly develop in th e tropics on every rising or stable cru stal segm ent, u p to altitu d es where1 high te m p e ra tu re s and a b u n d a n t p re cip ita tio n result in h e a v y w eathering an d are still sufficient to bring ab o u t a rap id lowering of th e relief. In B u lla ’s opinion it is th is form of sm oothing w hich is currently ac tiv e in th e tro p ical sav an n ah an d ra in forest areas. Because of its considerable ex ten t, he held I his process to be th e most frequent and m ost typical form of relief sm oothing on the E a rth . H e called it “ tropical tru n c a tio n ” and the sm oothed area resulting from th is he term ed "tropical p lan ated surface” .
In B u lla ’s in te r p r e ta tio n , th e ste p p e d a n d u n d u la tin g su rface e le m e n ts o f th ese tr o p ic a l p la n a te d su rfa ce s a r e e sse n tia lly in d e p e n d e n t of th e te c to n ic d isp la c e m e n ts of th e re g io n . He e m p h a size d t h a t th e tro p ic a l p la n a te d su rfa ce s o f to d a y c a n n o t, e x c e p t w ith th e u tm o s t cau tio n , b e u sed to in te r p r e t th e age a n d a m p litu d e o f ep eiro g en e tic o r d ic ty o g e n e tic d is p la c e m en ts, as tlie d e v e lo p m e n t of su c h su rfaces is in d e p e n d e n t of its r e la tiv e a ltitu d e a b o v e th e sea lev el; it m a y e x te n d fro m th e fla t co asta l p la in to q u ite c o n sid era b le a ltitu d e s (2,000 m ).
p ro v id ed th e c lim a tic co n d itio n s a re rig h t. I n th is l a t t e r re s p e c t B u lla ’s s ta n d p o in t is close to t h a t o f If. L o u is (1958, 1964) a lth o u g h f u n d a m e n ta lly d iffere n t fro m t h a t of B iid el, w ho c o n n e c ts— ju s t as D av is d id — th e fo rm a tio n o f sm o o th surfaces a lm o s t w ith o u t g r a d ie n t (2 p e r m ille) to a w ell-defined b a se le v el of ero sio n , a n d hold s th e h ig h tro p ic a l p la te a u x , for e x am p le t h e D eccan P la te a u , to be u p lifte d T e r tia r y p la n a te d su rfa ce s, w h ic h a t t h e p ro p e r tim e d e v elo p ed in close c o n n ec tio n w ith t h e c u r re n t b aselev el o f erosion.
A cco rd in g to B iid el (1965), an a c tiv e p la n a te d s u rfa c e su c h as th e S o u th In d ia n T a m iln a d P la in u n c e a sin g ly p e n e tr a te s a lo n g d e ep ly recessed v a lle y s in to th e h ig h e r su rface (th e D e cc a n P la te a u ) a n d , in th e pro cess, g r a d u a lly d ig ests it. In th is re sp e c t, his v iew s a re close to th o s e o f W . P e n c k . A lth o u g h B iidel co n sid ers his h y p o th e s is of th e “ d o p p e lte E in e b n u n g sflä c h e ”
— “ d u p lic a te p la n a tio n s u rfa c e ” — to be v a lid also for th e D eccan P la te a u . H e h o ld s, to g e th e r w ith B .P . R a d h a k ris h n a n (1952), t h a t th is p la te a u is to be a fossil su rfa ce . O n th e o th e r h a n d , Louis (1964), d is p u tin g B iid el’s view s, con sid ers, s im ila rly to B u lla , t h a t re c e n t tro p ic a l p la n a tio n is also p ossible on h ig h tro p ic a l p la te a u x . A cco rd in g to m y o w n e x p erien c e in th e field, B ü d e l’s v iew co n cern in g t h e D eccan P la te a u is ju stifie d in as m u c h as re c e n t p la n a tio n proceeds o n t h e p la te a u m arg in s an d alo n g deep e m b a y m e n ts o f b ro a d v a lle y s , w h e rea s t h e c e n tra I p o r tio n o f th e p la te a u c a n in d ee d be co n sid ered a fossil stu m p o f a p la n a te d su rfa c e . T his is s u p p o rte d b y th e slow d isse c tio n of hig h -lev el la te n te s .
Büdel’s hypothesis of th e “ doppelte E inebnungsfläehe” offers an a p p a ren tly plausible ex p lan atio n for th e step p ed halfplains (or th e so-called
“ S pü lp ed im en te” ) w ith a w id th of several hu n d red m etres and 20 to 30 m a ltitu d e differential on th e slopes of isolated m ountains (Inselbergs) an d on I he m argins of p lan ated surfaces.
The te rm “ step p ed p lan ated surface” is ju stified for steps w ith an a ltitu d e of several h u n d re d m etres th a t sep arate extensive tropical plan ated surfaces w ith cu rre n tly receding fronts an d m arginal zones dissected by valleys em bracing tro p ica l inselbergs. According to M. Louis (1964), although th e process of regression of the step fronts is in h arm o n y w ith the effects of lIn*
a c tu a l tro p ical clim ate, th e m arginal p a rts of higher p la n a te d surfaces an d I he step zone itself are dissected by th e b roadening valleys incised into th e m . I fence, the stepped surfaces arc necessarily due to a re p eated u p liftin g —or a repeated arch in g —according to Biidel. The ste p scarp recedes parallel to itself from th e seashore or from any oilier baselevel of erosion, preserving its s te e p
9 19
ness betw een th e tw o a d ja c e n t planes. T he developing tro p ical p lan ate d s u r
face of a b o u t 2 per m ille slope is also low ered parallel to itself. All in all, th is hypothesis applies to a tro p ic a l en v iro n m e n t in accordance w ith th e m ore fu n d am en tal ideas of th e D avisian polycyclic th eo ry an d of P enckian recessive slope evolution.
The in te rp re te rs of tro p ic a l p la n a tio n a n d their followers generally agree th a t this process was also in ancient tim e s th e m ost general process of relief sm oothing. T his is also th e e x p la n a tio n th e y offer for to d a y ’s ex tra tro p ical p lan ate d su rfaces w hich, in th e ir opinion, rep resen t re m n a n ts of T ertia ry or even older fossil surfaces.
(g) O ther p la n a te d surfaces
(1) T he lo c a l b a se le v e l o f a p la n a te d s u rfa c e f r e q u e n tly coincides w ith a r a th e r re s is ta n t la y e r of ro c k . I n su c h cases i t is o p e n to d isc u ssio n w h e th e r th e sm o o th e d su rface is a p e n ep lain (a stu m p ) o r s im p ly a d is s e c te d s t r u c t u r a l p la in . T h e v a lle y slopes a r e u su a lly s te e p a n d in f r o n t of th e m t h e r e a re in se lb e rg s c ap p e d w ith h a r d ro ck .
(2) C.M. C ric k m a y (1933) su g g e ste d re p la c in g t h e t e r m “ p e n e p la in ” as a form of d e n u d a tio n by th e te r m “ p a n p la n e ” . H e h e ld t h a t D a v is ’s cy cle o f e v o lu tio n is n o t realized b e ca u se o n ly th e in itia l s ta g e s o f th e cy cle o f e ro sio n c a n he v e rifie d . T h e cycle th e o r y is “ a d e d u c tio n by som e of th e g r a n d m a s te rs of g e o g ra p h y a n d g eo lo g y , a n d m ere ly b lin d su b m issio n o n th e p a r t of th e r e s t ” . T h e p a n p la n e is, a c c o rd in g to C ric k m a y , a p ro d u c t o f la te ra l s tre a m e ro sio n . B etw een t h e v a lle y s b ro a d e n e d b y i t , th e d iv id e s a re g r a d u a lly d ig e s te d a n d low ered. H o w ev e r, it w ould be d iffic u lt to re p la c e t h e p e n e p la in c o n c e p t b y th e a b o v e d efin itio n a lth o u g h th e re u n d o u b te d ly e x is t p la in s s c u lp tu r e d b y b ro a d l a te r a l erosion.
T his is w h y a r e s tr ic tio n o f t h e te r m p a n p la n e h a s b e en s u g g e ste d (T h o rn b u ry , 1954), lim itin g it to b a n d s s m o o th e d b y l a te r a l e ro sio n a lo n g th e flo o d p lain s o f rivers.
(3) T he t e r m e tc h p la in h a s b e e n u sed for so m e tim e b y se v e ra l re se a rc h e rs, e.g. b y E . .1.
W a y la n d (1943) in U g a n d a , to d e s ig n a te som e s m o o th e d surfaces a rra n g e d stepw ise below th e C retaceo u s p la n a te d su rfa c e . W a y la n d h e ld th e s e fo rm s to h a v e d ev elo p ed o n t h e d eep ly w e ath e red s u rfa c e o f a ste p w is e u p lif te d p e n e p la in , b y m a rg in a l d o w n w ea rin g in p e rio d s of te c to n ic re s t.
(4) As n o t a ll r e m n a n ts o f e ro sio n a l su rfa c e s c a n b e called p e n e p la in s o r p la n a te d su rfa ce s in th e D a v isian (o r a n y o t h e r g e n e ra l) sen se, t h e t e r m “ p a r tia l p e n e p la in ” has b een u se d by v a rio u s w o rk e rs. T h e t e r m w as o rig in a lly co in ed b y D a v is for fo rm s o f d e n u d a tio n t h a t w e n 1 h e ld u p in th e e a r ly s ta g e s o f e v o lu tio n . T h e a d h e r e n ts of th e cycle th e o r y in te r p r e t th is b y assu m in g t h a t , o f t h e su ccessiv e cycles o f e ro sio n in a g ra d u a lly ris in g reg io n , th e la te r ones te n d to be less c o m p le te t h a n th e e a rlie r o n es, t h a t is to sa y t h a t t h e succesion te n d s to w a rd less an d less c o m p le te cy cles. H o w e v e r, e v e n w o rk e rs w ho do n o t a c c e p t th e cycle id e a use th is te rm , f ir s tly for p a r tly s m o o th e d su rfa c e s a r ra n g e d step w ise b y g ra d u a l u p liftin g , and seco n d ly for s m o o th e d s u rfa c e s w h ic h g e o m o rp lio lo g ica lly o r to p o g ra p h ic a lly do n o t fully m e rit th e t e r m “ p e n e p la in ” . In t h is l a t t e r sen se, t h e te rm s “ p r im a r y p e n e p la in ” , “ in itia l” o r
“ local p e n e p la in ” a re also in u se. Y e t o th e rs , w h o w ish to av o id a n y u se o f the te r m p e n e p la in , use v ario u s s y n o n y m s o f r a th e r d iv e rs e c o n te n t fo r th e a b o v e c o n c e p ts : d e n u d a tio n a l level (Cys, 1965). e ro sio n s u rfa c e -le v e l (M azu r, 1965), s u rfa c e of p la n a tio n (C z u d e k -D e m e k —S te h - lik, 1965; M isliev—P o p o v . 1965). T h e p r e s e n t a u th o r s su g g ested th e te rm “ p la n a te d s u rfa c e ” o r “ su rface o f p la n a tio n ” .
(5) On th e m a rg in s of th e m o u n ta in s , o r in t h e b ro a d e m b a y m e n ts of th e v a lle y s t h a t p e n e tr a te in to th e m , s m o o th e d su rfa ce s f r e q u e n t ly form tr a n s itio n s to w a rd s fo rm s of a c c u m u la tio n a n d d e n u d a tio n o r o f p u r e a c c u m u la tio n . T hese form s a n d th e ir te rm in o lo g y will be d e a lt w ith in t h e s e c tio n on p e d im e n ta l h a lf-p lan e s a n d special h a lf-p lan e s.
2. PEDIMENTAL IIALF-PLANES
(a) Pedim ent (Gebirgsfussfläche)
T he in te rp re ta tio n a n d definition of pedim ents in geom orpliologieal lite ra tu re are also ra th e r v aried . The te rm was originally coined h y W . J . McGee
1897) who m eant h y it a gently sloping plane scu lp tu red ou t of h a rd rock, foreset to the steep m o u n tain slopes (Thornbury, 1954). In his opinion, the surface of the ped im en t is covered b y ju st as m uch d e tritu s as can he tra n s
p o rted by slopewash in a sem iarid clim ate.10
D. W. Johnson (1932a) also included under th e h eading of pedim ent all surfaces of accum ulation which connect the baselevel of erosion to th e tru n ca te d rock surfaces of th e m ountain, th e thickness of whose d etric al cover increases aw ay from th e m ountain. U nder his influence, even surfaces stand- in»' m ore or less u n d e r th e regim e of accum ulation on th e m o u n tain m argins w ere interp reted as pedim ents.
In N orth A m erican lite ratu re , four general groups of pedim ent have been distinguished:
(a) (typical) pedim ent (b) dissected pedim ent
(c) buried or cryptopedim ent (d) coalescing pedim ent.
B ilateral p ed im en tatio n results in a gradual digestion of th e m o untain m ass or of the resid u al m ountain. In this sense, w hen pedim ents coalesce a fte r having digested th e entire m o u n tain mass, a pediplain comes to exist (H ow ard, 1942).
L ately the stu d y of th e regional ex ten t, the in te rp re ta tio n of th e origin an d th e clarification of th e term inology of pedim ents has been un d ertak en largely by E uropean w orkers (B irot, Bohck, C hiehagov, Dresch, J o ly , Men- sehing, P iotrovsky, R ay n al, S piridonov, Wiche, an d others).
According to D resch (1951, 1957a), French lite ra tu re m akes a sh a rp distinc
tion betw een (1) ped im en ts p roper—surfaces scu lp tu red in h ard rock, often the crystalline, in th e forelands of m ountains, an d (2) glacis, scu lp tu red in soft rock and loose deposits.
10 I n A m erican m o rp h o lo g ic a l lite r a tu r e , th e process o f p e d im e n ta tio n is a ttr ib u te d to v a rio u s agencies:
(a) S h e e t erosion (M cG ee, 1897): th e d e tr itu s m oved by slo p ew ash w o rk s a s tr o n g corrosive p la n a tio n on th e h a r d ro c k of th e m o u n ta in foreland.
(b ) L a te ra l p la n a tio n (B lack w eld er, 1931: J o h n s o n , 1932a) p la n a lio n is d u e to late ra l e ro s io n a n d corrosion b y riv e rs a n d t o r r e n ts in sem iarid re g io n s ; tw o c o m p o n e n ts o f th is p ro cess a re assum ed:
(i) la te ra l erosion a t t h e m o u th s o f v a lle y s on th e m o u n ta in m a rg in , (ii) dep o sitio n o f a llu v ia l fans b y r iv e rs issu in g from t h e m o u n ta in s .
(c) T h e co m b in a tio n th e o r y (D av is, 1930: R ich, 1935; S h a rp , 1940) co n sid ers as th e m o st im p o r ta n t factors o f p e d im e n ta tio n
(i) th e m ec h an ic al c o m m in u tio n of h a rd rocks, (ii) slopew ash a n d
(iii) so-called la te ra l p la n a tio n .
I n R ic h ’s opinion, p e d im e n ta tio n , to g e th e r w ith th e p ro d u c tio n o f d e tr itu s a n d th e fo rm a tio n o f a llu v ial fans, is t h e n o rm al and g e n e ra l form of p la n a tio n in a rid a n d se m ia rid regions.
I le co n sid ers th e ro le o f la te r a l erosion to be in essen tial to th e s c u lp tu re o f p e d im e n ts . 21
P e d im e n la tio n is considered b y Jj. C. K ing (1962) th e m ost general process of p lan atio n , no t o n ly under arid a n d sem iarid clim ates bu t also in the tropics w ith one rainy sea so n and u n d e r M editerranean, an d to som e ex te n t, also u n d e r tem p erate clim ates. He holds t h a t once th e steep scarp of a retreatin g p e d im e n t step h as developed a g a in s t th e m o u n ta in flank, it stay s th a t way u n til the advance of th e g en tly sloping pedim ent digests th e e n tire m ountain.
As a result, the p ed im en t becom es a pediplain.
(b) Glacis
A lthough the F ren c h au th o rs (B iro t, Dresch, D um as, T rica rt, an d others) s h a rp ly distinguish th e soft-rock glacis from th e pedim ent, au th o rs from o th e r countries (M ensching, 1958 b ; W iche, 1963) use th e te rm pedim ent- in a b ro a d e r sense, as a synonym of th e G erm an “ F ussfläche” an d th e French
“ g la c is” . However, th e re seems to be a fairly w ide consensus of opinion that half-planes foreset to m ountains fall into several groups of different position, o rig in and co n stitu tio n . B irot a n d Dresch (1966) distinguish th re e main g ro u p s among th e glacis s c u lp tu re d in soft rocks, or in loose deposits:
(a) Glacis of ero sio n or ab latio n . T he tru n c a te d soft rock crops o u t on the su rfa ce, or is covered b y ju s t a th in sheet of allu v ial—proluvial deposits.
(b) Buried glacis o r ancient glacis of erosion, covered b y a sheet of a llu v ial- p roluvial deposits: ac cu m u latio n is fa ste r th a n d enudation.
(c) Glacis of p u re ac cu m u latio n , or, as som e call it, glacis fans. They fre q u e n tly resem ble g e n tly sloping alluvial fans a n d develop o u t of garlands of allu v ial cones of to rre n ts , lean in g ag ain st th e m o u n tain slopes. Some w ork
ers distinguish also glacis slopes a n d glacis terraces. The form er rise steeplv a b o v e the erosional glacis covered b y a thin sheet of w aste, an d join the rock ledges on the fo re fro n t of th e m o u n tain s. On th e o th e r h a n d , glacis terraces d ev elo p far from th e m o u n tain fro n t, near th e low er p a rt of th e half-plane foothill, and c o n s titu te forms of tra n sitio n b etw een glacis of accum ulation a n d stre a m terraces.
T h ere is p resen tly a fairly 1 ively discussion a b o u t w hether it is necessary to m ak e a genetic d istin c tio n b etw e en glacis a n d pedim ent. The conditions of glacis form ation as indicated b y th e French a u th o rs are an a rid —semiarid clim a te , with in te n se physical com m inution, periodic m ass w asting and slopew ash, to w hich som e a u th o rs a d d lateral erosion. A ccording to Dresch, how ever, the ev o lu tio n of a glacis is b o u n d to the baselevel of erosion, whereas a p ed im ep t is m uch m ore in d e p e n d e n t in this respect. On th e o th e r hand, H . M ensching an d H. R av n al (1954) h av e p ointed o u t th a t, th e half-planes in th e forelands of m o u n tain s being of a highly com plex origin, it is b e tte r to av o id concepts h a v in g a co n n o ta tio n of a single ex tern al agency (glacis d ’erosion). They hold the term s piedm ont surface, glacis dc piedm ont or piedm ont-glacis, m ean in g w aste-covered half-planes in the forelands of m oun
ta in s , to be m ost conv en ien t. The te rm “glacis te rra c e ” should refer to te r
ra ces developed by stre a m s incised in foreset half-planes (piedm ont-glacis o r glacis of accu m u latio n ), reach in g from the m o u n tain front tow ards the m a in valley. These form s are not id e n tic a l geneticallv w ith valley terraces in t he u su al sense.
22
úr) V alley pedim ents
In geom orphological term inology and lite ra tu re there has re c e n tly cropped u p a special te rm for ra th e r n arrow half-planes (of a few h u n d re d m etre s’
w id th ), joining th e alluvial-plain or terrace surfaces of b ro a d valleys and th e la te ra l slopes of interfluvial divides. Such planes are o ften sculptured in h a rd rock, b u t th e y also occur in soft rock. The oblique slope of the h alf
plane is occasionally covered w ith a th in sheet of deluvial, colluvial or eluvial deposits. These “ valley p e d im en ts” , pedim ent-like surfaces a b o u t th e higher portions of riv er valleys in th e te m p e ra te zones,11 have n o t y e t been studied in sufficient d etail to permit a genetic com parison w ith ty p ic a l glacis or pedi
m en t forms. I t is, how ever, a n open question w hether it is a t all justified to distinguish “ v alley p ed im en ts” from these la tte r.
The process of evolution of “ valley p ed im en ts” sculptured in h ard rock is un clear as yet. In some cases th is slope is alre ad y dissected in to la te ra l ridges of equal height. In some m o u n tain s such form s occur in several generations a t different a ltitu d e s, th a t is to say, in th e form of lateral ridges issuing from I he larger in teiflu v ial divides.
S o m e “ v alley p e d im e n ts ” c o n v erg e w ith th e o ld e r, e a rly P le is to c e n e, o th e r s w ith th e y o u n g e r, late P le is to c e n e te rra c e s (P é c si, 1959). I n th e case o f th e fo rm e r, t h e a ss u m p tio n o f a n e a r ly P leisto cen e o rig in is ju stifie d . I n som e cases, th e p re su m a b ly o ld e s t — U p p e r P lio cen e — “ v alley p e d im e n t” (or th e g lacis in h illy reg io n s o f loose d e p o sits) p a sse s w ith a g e n tle b r e a k in to th e s u rfa c e o f th e in te rflu v ia l d iv id e. I n t h e a b se n ce of s u ita b le re g io n a l c o m p a ra t iv e s tu d ie s it is d iffic u lt to te ll h o w th e so-called “ v a lle y p e d im e n ts ” a re r e la te d to F . B a sc o n ’s t e r m “ b e rm ” (1931) o r to W . H . B u c h e r ’s “ s t r a t h ” (1932) o r th e fo rm s d e n o te d b y th e s e te r m s . B o th c o n cep ts w ere a p p lie d b y th e i r a u th o rs to su rfa ce s of p la n a tio n , “ i n itia l” o r “ p a r tia l p e n e p la in s ” d e v elo p ed in b ro a d v a lle y s o f ero sio n , o w in g to th e i n te r r u p t io n o f a cycle o f e ro sio n . A ccording to B u c h e r, a “ s t r a t h ” in th e s t r i c t sense is a h a lf - p la n e d e v elo p ed by l a te r a l erosion on t h e v a lle y b o tto m ; a f te r em ersio n , i t c a n b e developed f u r t h e r b y a n y o th e r a g e n c y . Such s u rfa c e re m n a n ts h a v e a lr e a d y b een d e sc rib e d as “ s t r a t h t e r r a c e s ” . H en ce, in a g e n era l w ay , t h e te rm s “ b erm a n d s t r a th te r r a c e ” a r e re s tric te d to t h e p in n a te d su rfaces m e rg in g in to th e v a lle y flanks.
id) M arginal ledges
U nder a te m p e ra te clim ate th ere occur, m ainly aro u n d funnel-shaped v alleys p en e tratin g into b lo ck fau lted m o u n tain s, some n a rro w m arginal ledges sculptured in h ard rock. These form s are usually re stric te d to th e m o u n ta in m argin looking dow n upon th e funnel-shaped v alley . In o th er places, however, w here th e interfluvial ridges are narrow or th e openings of I he valleys are close to g eth er, th e y extend also to ihe forefronts of the inter- lluvial ridges. On th e o ther h a n d , in sections where valley openings on th e m o u n tain front are w ide-spaced, th e frontal slope is u ndissected an d steep.
These stepped ledges, or occasionally step p ed pedim ental half-planes, can he considered each as th e ro o t of an earlier pedim ent surface or piedm ont- glacis, preserved on ihe m argin of the m o u n tain block uplifted since (Pécsi,
1963b, 1966). 11
11 I n som e tro p ic a l reg io n s th e s e a re m u c h m ore co n sp icu o u s, e.g. w e s t o f P o o n a on th e D eccan tr a p b a s a lt su rfa ce .
