A technique for classifying hill-slopes on the basis of measurable morphological attributes is described and illustrated. Four components of hill-slope morphology are identified. These are dimension, shape, slope and degree of surface irregularity. From field measurements of hill-slopes, surveyed in measured lengths, best segment profiles (Young, 1971) are obtained and for these profiles sixteen measurable attributes that summarize the four components are defined. On the basis of these attributes, hill-slope profiles from New South Wales, Australia and the Xavantina-Cachimbo area, Brazil, are classified using a hierarchic unweighted pair-group clustering strategy. In the former area the grouping achieved agrees with subjective assessment of similarities of hill-slope forms and in the latter corresponds closely with the subjective interpretation of types made by Young (1970). Objective numerical techniques of this type are recommended for general use for the identification of hill-slope types. WITHIN the geomorphological literature several examples exist of attempts to classify a number of measured hill-slopes in such a way that the members of each class have a similar morphology. Thus, for example, Young (1970) measured 82 hill-slope profiles in the Xavantina-Cachimbo area of Brazil and subsequently classified them into six hill-slope types. But although geomorphologists have found it necessary to express the forms of a large number of hill-slopes in terms of a small number of hill-slope types, no objective technique has been developed for this purpose. Although Blong (1975) discusses hill-slope types in a study in New Zealand, he does not attempt to provide a general methodology for the classification of hill-slope forms. It is the purpose of this paper to describe and illustrate the use of a technique for classifying hill-slopes, surveyed in measured lengths, on the basis of measurable morphological attributes derived from the measured form. Because such a classification is, in fact, a classification of attributes, it is necessary to examine first the derivation of these attributes from the actual hill-slope profile. THE DESCRIPTION OF HILL-SLOPE FORM It is not possible to measure precisely the actual form of a naturally occurring hill-slope. The form as measured is necessarily an approximation of the actual form and the accuracy of this approximation will depend to a large extent upon the technique of measurement. For the measured form of a hill-slope profile surveyed in measured lengths, Savigear (1967) has proposed the term measured length profile. Clearly, for any one actual hill-slope profile surveyed in measured lengths, many measured length profiles exist, each one corresponding to a different choice of measured length. For comparison of hill-slopes it is advisable to use the same measured length for all surveyed profiles: one of 5 m has been found convenient, and this value has been recently proposed for general use (Young, 1974). The measured length profile consists of a sequence of rectilinear sections (measured lengths) separated by angular discontinuities. These angular discontinuities may reflect actual discontinuities within the hill-slope profile or may result from the technique of survey (see Savigear, 432 This content downloaded from 157.55.39.104 on Mon, 20 Jun 2016 06:21:35 UTC All use subject to http://about.jstor.org/terms Hill-slope forms 433 1967, p. 227). In order to remove those discontinuities that result from the technique of survey, Savigear analysed visually the measured length profile to identify from it the units (segments and elements) of which the profile is composed, and thus defined the unit profile. More recently, Young (1971) has described an objective technique (termed best units analysis) for the identification of such units. Within this technique it is possible to identify separately best segments, best elements and best units. It has been argued elsewhere (Parsons, 1973) that if hill-slopes are treated as sequences of segments (rather than segments and elements) their comparison is easier. Accordingly, best segments analysis (using a value of i o per cent for Vamax) is carried out on the measured length profile to define the segment profile. It is from the segment profile that all the attributes of morphology, upon which classification is based, are derived. It is possible to identify four components of hill-slope morphology: (i) dimension; (ii) shape; (iii) slope, or steepness; (iv) degree of surface irregularity. To describe each of these components, one or more measurable attributes can be defined. Hill-slope length, for example, is a measurable attribute that describes hill-slope dimension. For each of these four components of hill-slope morphology, the measurable attributes that will be used to describe that component are now defined. Dimension Two attributes are defined which are used to describe the dimensions of a hill-slope: (i) length of the hill-slope (in metres); (ii) height range of the hill-slope (in metres). Shape The shape of a hill-slope is described by two attributes: (i) Hill-slope curvature. Hill-slope shape may be expressed in terms of convexity and concavity. Figure i shows graphs of four simple hill-slope profiles (a. convex; b. concave; c. recti-