Appropriate terminology for karst-like phenomena: the problem with 'pseudokarst'

Headnote

Abstract: The practice of referring to certain morphologically karst-like phenomena as 'pseudokarst' is problematic, because it ignores basic principles of sound classification, logical naming conventions and accepted geomorphic classifications and terminology. These problems have compounded the difficulty in establishing an accepted classification of 'pseudokarst' types. The practice embodies a karst-centric perspective which should be avoided in favour of using conventional geomorphic terminology for non-karstic features. We illustrate this by providing existing conventional terms for many 'pseudokarst' types reported in the literature.

Keywords: karst; pseudokarst; landform classification; geomorphology; Tasmania

Received 19 November 2012; Revised 5 February 2013; Accepted 6 February 2013

Karst is defined with reference to the enhanced solubility of certain rock types in natural waters, the consequent importance of aqueous dissolution and precipitation as dominant geomorphic drivers, and the resultant characteristic landforms and hydrology (Jennings, 1985; Gillieson, 1996; Ford & Williams, 2007; ). This is consistent with accepted practice for classifying landforms according to morphogenetic criteria, recognising that similar morphologies can result from quite different geomorphic processes. However the alternatives of either purely morphologybased or purely genesis-based approaches to landform classification would not be satisfactory for elucidating the history of landscapes, which is a fundamental aim of geomorphology.

Despite near-universal acceptance of a morphogenetic definition of karst, we note a tendency to apply morphology-based criteria to accommodate discussion of various non-karstic but karst-like phenomena (Grimes, 1975; Vitek, 1987; Halliday, 2004, 2007; CRCCS, 2008). We refer to the problematic term 'pseudokarst'. Aspects of this term are discussed in several papers and some criticisms have been made previously. Otvos (1976) argued that morphology alone was not an adequate basis for designating 'pseudokarst', and recommended that the term should be applied only in the case of piping and 'thermokarst' forms. The latter term has been used with reference both to cavities in glaciers and depressions due to melting of ground ice in permafrost. Although not always explicitly used as a class of 'pseudokarst' (e.g. French, 2007), 'thermokarst' likewise has misleading connotations of a karstic dimension to non-karstic phenomena. Cigna (1973, 2008) stressed physicochemical criteria in differentiating between karstic and karst-like terrains, recognising a spectrum of 'karstic' types (hyperkarst, karst, parakarst, hypokarst, pseudokarst). The definitional basis of karst and 'pseudokarst' has also been raised in the context of cavernous silicate terrain, informing suggestions that karst itself requires a new definition (Martini, 2004). Simmert (2011) expressed reservations at using 'pseudo' as a prefix for karst-like phenomena, but did not propose an alternative. We contend that these contributions do not resolve problems of a more fundamental nature which we identify below.

Specifically, we argue that the term 'pseudokarst' is (a) poor classification practice in principle; (b) unnecessarily duplicates mainstream approaches to landform classification; and (c) is a karst-centric terminology for non-karstic phenomena. Each of these objections is discussed below.

(a) Poor classification practice

We propose that scientifically-based classifications should be and generally are underpinned by certain basic principles, including that: (1) a demonstrable need exists for the classification; (2) the scope of features included has an objective basis; (3) categories within the classification are mutually exclusive; and (4) the constituent elements are differentiated and named according to what they are, not according to what they are not. The class of 'pseudokarst' fails to comply with each of these principles. There is no demonstrable need for the term because the landforms concerned are already logically classified using conventional geomorphic terminology, which adequately covers both their morphogenetic classification and their morphological similarities to karst (see below). The scope of 'pseudokarst' is arbitrary, lacking an objective basis because it is generally concerned with a narrow subjectively-defined range of karst-like landforms, most commonly although not exclusively caves and enclosed depressions, that ignores much of the diversity of actual karstic landforms. Categories proposed for classifying 'pseudokarst' tend not to be mutually exclusive, due to an emphasis on similarities in form between otherwise very different features as a primary defining characteristic. This can lead to confusion and awkward classification hierarchies as noted further in (b) below. Finally, as a means of classifying landforms 'pseudokarst' (literally 'false karst') is not a valid form of differentiation and naming, since it lacks meaning in itself without reference to karst. That is to say, the notion of 'pseudokarst' classifies things according to what they are not, rather than according to what they are. This problem was recognised by Simmert (2011); it cannot be a logical basis for the classification of natural phenomena.

(b) Unnecessarily duplication of mainstream geomorphic classifications

Whereas 'pseudokarst' as an umbrella term is typically defined primarily with reference to morphology, 'pseudokarst' proponents classify subtypes according to a sometimes confusing mix of form, process and fabric. Grimes (1975) adopted a processbased classification depending on whether eroded material is transported in a solid, liquid or gaseous state. Vitek (1987) proposed a classification based on both morphology and scale. Halliday (2004, 2007) recognised some mainly process-based categories, such as 'rheogenic pseudokarst' (lava flow forms), some mainly morphology-based categories, such as 'crevice pseudokarst' (fractured volcanic rocks, sea caves, glacial crevasses) and some mainly fabric-based categories, such as 'talus pseudokarst' (interstitial cavities due to weathering or mass movement) and 'compaction pseudokarst' (landslide and avalanche deposit forms). In some cases trivial parallels have been invoked while ignoring fundamental differences in scale, process and context. For example, Halliday (2004) implied that the 'water-filled cavern beneath the Ross Ice Shelf' (i.e. the underlying ocean) is a form of 'glacier pseudokarst'. No apparent consensus on a unifying classification of 'pseudokarst' types has emerged.

Consequently, literature on 'pseudokarst' often relies strongly on conventional geomorphic terminology and explanations, especially at the level of case studies of specific landforms. This is an entirely logical approach which we consider implicitly acknowledges the confusion that arises from the exclusive use of 'pseudokarst' terminology. Some recent papers reference 'pseudokarst' only as a keyword (e.g. Grimes, 2006; Smith, 2007). On the other hand, new terms have been proposed for features which can be described more simply using existing terminology. A selection of such terms and conventional geomorphic terms for the same features is listed at Table 1. This illustrates our point that appropriate terminology and classifications are already available for the relevant phenomena, and we believe these should be used. The fact that the term 'pseudokarst' is defined in key earth science references (e.g. Neuendorf et al., 2005) indicates a history of use but is not justification in itself.

The complexities and confusions (above) that arise when attempting to make non-karstic phenomena fit into an arbitrarily-defined category such as 'pseudokarst' underscore our assertion that this is poor classification practice which unnecessarily duplicates existing classifications. This is reinforced by Figures 1 to 3, which show morphologically karstlike landforms at two sites in Tasmania. Both sites have been cited as examples of 'pseudokarst', yet are more informatively described by conventional terminology.

(c) 'Pseudokarst' is karst-centric terminology

The term 'pseudokarst' embodies an assumption that karst is an appropriate benchmark for defining many non-karstic phenomena. There is no objective basis for this very karst-centric perspective, which has been pursued under the auspices of the International Union of Speleology Pseudokarst Commission, although the term itself was reportedly first used by the geologist von Knebel (1906) with reference to lava features, apparently in an attempt to clarify that certain features were not actual karst (Halliday, 2004; Simmert, 2011). We note that to varying degrees virtually all landforms including karstic ones have morphological analogues developed under different process regimes. Therefore, it serves no purpose to blur the distinction between features with very different process histories by focussing on superficial similarities of form, as in the example of 'pseudokarst'. The same principle applied more widely would imply scope for unlimited classes of 'pseudo' features. For example vulcanologists could describe karst caves as 'pseudo-lava tubes' which would clearly be an absurd outcome yet is based on an equivalent logic to that which underpins the notion of 'pseudokarst'.

In summary, 'pseudokarst' is not an appropriate umbrella term for describing morphologically karstlike phenomena; nor does it provide an appropriate framework for classifying the relevant phenomena, as these are more usefully covered by established geomorphic classifications and terminology. The term 'pseudokarst' makes little sense from any geomorphic perspective other than a very karst-centric one, and as such does not complement or extend more broadly accepted classifications and terminology, as used amongst the wider community of geomorphologists. Indeed, the use of the term 'pseudokarst' has arguably contributed to a lack of clarity regarding the scope of (true) karst studies, as manifest in the debate regarding whether solutional landforms in silicate rocks are karst or 'pseudokarst' (Wray, 1997; Martini, 2004; Aubrecht et al., 2011; Sauro et al., 2012). It seems possible that the perceived importance in some quarters of maintaining a distinction between karst and 'pseudokarst' has delayed broader acceptance of solutional landforms in silicates as a valid form of karst.

In rejecting the term 'pseudokarst' we do not dismiss the importance of scientifically documenting the wide range of landforms with karst-like attributes, or the validity of adopting a thematic morphological approach to this, provided it is done using language that does not obscure fundamental geomorphic differences. Thus for example the use of the morphological themes of 'caves' or 'enclosed depressions' developed through a variety of processes including karst achieves the same purpose as that of 'pseudokarst', and does so using broadly accepted terminology that complies with good classification practice. We contend that relevant studies will extend their scope and impact by adopting this approach.

Sidebar

Citation: Eberhard R. and Sharples C., 2013. Appropriate terminology for karst-like phenomena: the problem with 'pseudokarst'. International Journal of Speleology, 42 (2), 109-113. Tampa, FL (USA) ISSN 0392-6672 http://dx.doi.org/10.5038/1827-806X.42.2.2

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