Climatic geomorphology
31
(2, 3) Periglacial zone of pronounced valley-cutting. This corresponds to the subpolar and
also solifluction regions of Biidel (1948), due to the importance of mass movements
on periglacial slopes. Its northern area is limited by glaciers and the southern one by
the solifluction boundary of the tree-cover or permafrost termination. The forest
limits usually coincide with the solifluction one, whereas the permafrost boundary
can expand over lower latitudes. The upper horizon of the ground is structured,
thus generating patterned ground. One of the main problems in these zones is rapid
fluvial incision. Slopes may develop by parallel retreat, generating tripartite
hillslopes.
(4) Ectropic zone of retarded valley-cutting. The most diverse and possibly the most
complex region, with the occurrence of a large number of different landforms.
Some 95 per cent of the landscape in the European sector of this area is constituted
by inherited landforms. The stepped planation surfaces (Piedmonttrepen of
W. Penck) are very common. Glacis surfaces and not very deep, wide valleys
may be characteristic. In those areas subjected to ancient glacial erosion, extensive
landscapes of hills and lakes are developed. Finally, an important sheet-cover of
loess derived from materials deposited during previous cold periods commonly
coats the ground. This, together with the following region, are the most important
ones for the study of climatogenic geomorphology.
(5, 6) Subtropical zone ofmixed relief development. This comprises the Mediterranean and
monsoonal regions which hold different morphological and climatic characteristics.
Bi.idel did not develop descriptions of the monsoonal regions, and instead just
adjusted his observations for the Mediterranean areas. This zone is a transitional area
for which its evolution has been affected by tropical, periglacial, glacial, temperate
humid and arid climates. In addition in this climatic type it is necessary to consider
human influences, which have an extraordinary impact on the occurrence of fluvial
erosion. The morphologic result is the assemblage of relict and modern landforms,
commonly arranged in an altitudinal zonation. A considerable development of
Tertiary planation surfaces is recognized in associated calcareous and in karstic
landforms. In the fluvial valleys and intramontane basins the development of glacis is
common in relation to the occurrence of fluvial terrace systems.
(7, 8) Arid zone of surface preservation and transformation through pediments and glacis.
This area includes that of winter-cold deserts and tropical arid zones. In this
latter zone a relevant intensity of wetting and drying and salt weathering processes
occurs. Within this zone erosion plains with inselbergs, extensive hamadas and
stone deserts are the usual features. In areas of limited relief the alluvial materials
of glacis and terraces usually develop calcrete crusts. These alluvial materials
constitute the main source area for the adjacent sand deserts. The winter-cold arid
zones constitute a transformation area rather than a region for later development of
planation surfaces. Frost cracking is the dominant weathering process. The most
representative landforms are the glacis systems.
(9) Peritropical zone (humid-dry) of excessive planation. In this region thick horizons
of chemical weathering commonly develop, which can reach several hundred
meters thick, with the eventual development of laterites. The formation of extensive
plains can be explained by the double planation mechanism of Bfidel (1957) for
tectonically stable areas, in which etchplains and inselbergs are characteristic.
31
(2, 3) Periglacial zone of pronounced valley-cutting. This corresponds to the subpolar and
also solifluction regions of Biidel (1948), due to the importance of mass movements
on periglacial slopes. Its northern area is limited by glaciers and the southern one by
the solifluction boundary of the tree-cover or permafrost termination. The forest
limits usually coincide with the solifluction one, whereas the permafrost boundary
can expand over lower latitudes. The upper horizon of the ground is structured,
thus generating patterned ground. One of the main problems in these zones is rapid
fluvial incision. Slopes may develop by parallel retreat, generating tripartite
hillslopes.
(4) Ectropic zone of retarded valley-cutting. The most diverse and possibly the most
complex region, with the occurrence of a large number of different landforms.
Some 95 per cent of the landscape in the European sector of this area is constituted
by inherited landforms. The stepped planation surfaces (Piedmonttrepen of
W. Penck) are very common. Glacis surfaces and not very deep, wide valleys
may be characteristic. In those areas subjected to ancient glacial erosion, extensive
landscapes of hills and lakes are developed. Finally, an important sheet-cover of
loess derived from materials deposited during previous cold periods commonly
coats the ground. This, together with the following region, are the most important
ones for the study of climatogenic geomorphology.
(5, 6) Subtropical zone ofmixed relief development. This comprises the Mediterranean and
monsoonal regions which hold different morphological and climatic characteristics.
Bi.idel did not develop descriptions of the monsoonal regions, and instead just
adjusted his observations for the Mediterranean areas. This zone is a transitional area
for which its evolution has been affected by tropical, periglacial, glacial, temperate
humid and arid climates. In addition in this climatic type it is necessary to consider
human influences, which have an extraordinary impact on the occurrence of fluvial
erosion. The morphologic result is the assemblage of relict and modern landforms,
commonly arranged in an altitudinal zonation. A considerable development of
Tertiary planation surfaces is recognized in associated calcareous and in karstic
landforms. In the fluvial valleys and intramontane basins the development of glacis is
common in relation to the occurrence of fluvial terrace systems.
(7, 8) Arid zone of surface preservation and transformation through pediments and glacis.
This area includes that of winter-cold deserts and tropical arid zones. In this
latter zone a relevant intensity of wetting and drying and salt weathering processes
occurs. Within this zone erosion plains with inselbergs, extensive hamadas and
stone deserts are the usual features. In areas of limited relief the alluvial materials
of glacis and terraces usually develop calcrete crusts. These alluvial materials
constitute the main source area for the adjacent sand deserts. The winter-cold arid
zones constitute a transformation area rather than a region for later development of
planation surfaces. Frost cracking is the dominant weathering process. The most
representative landforms are the glacis systems.
(9) Peritropical zone (humid-dry) of excessive planation. In this region thick horizons
of chemical weathering commonly develop, which can reach several hundred
meters thick, with the eventual development of laterites. The formation of extensive
plains can be explained by the double planation mechanism of Bfidel (1957) for
tectonically stable areas, in which etchplains and inselbergs are characteristic.