Cryopedology—The Study of Frozen Ground and Intensive Frost-Action With Suggestions on Nomenclature

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INTRODUCTION

Study of the action of frost, particularly in the Arctic and in areas having a periglacial climate during the Ice Age, goes on apace. However, discussion of the problems involved is handicapped and confused by the awkwardness and inadequacy of available terms. The present paper is concerned with the propriety of introducing some order into the terminology by the adoption of new terms and the modification of certain older ones. All future needs cannot be anticipated but the proposals here made should give a measure of relief.

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THE GENERAL PROCESSES

In our textbooks, discussion of weathering and erosion is largely confined to types of activity current in temperate climates. The relatively modest role of frost-action in temperate climates can be described with ordinary English words. "Frost" has, according to Webster, several meanings: (1) the act of freezing, applied chiefly to water; (2) the state of the air which occasions freezing; (3) frozen dew or hoarfrost; (4) metaphorically, coldness of temperament, etc. The first two senses are those commonly in use in geological discussions. The word is also a verb, "to frost," in which the meaning is more confused: (1) to frost or freeze vegetation; (2) to cover with hoarfrost and hence (3) to produce a "frosted" or matte surface on cake, metals, or other substances. In order to describe the action induced by freezing and thawing, geological writers have been forced to compound the terms "frost-action" and "frost-work." Webster does not define "frost-action" but the meaning of "frost-work" is given as the pattern of ice crystals on a windowpane or other surface.

Thus the general use by geologists of "frost-action," "frost-work," "frost-splitting," "frost-split," "frost-riving," "frost-riven," "frost-heave," and "frost-heaved" is not completely supported by dictionary definitions. However, these terms are all perfectly derived verbal nouns and adjectives of self-evident meaning. There is, however, no way of deriving from these verbal expressions corresponding nouns for the products of the varieties of action that they imply. All that can be done is to use expressions such as "materials produced by frost-action," or "frost-sprit fragments" or "frost-heaved ground." Experience shows that such roundabout expressions are awkward and inadequate. Several terms have been introduced for particular frost-born products but no satisfactory general terms of wide connotation have yet been brought forward.

THE NEW SUB-SCIENCE—CRYOPEDOLOGY

The present wave of interest in the Arctic, stemming from the recent war, involves studies in both pure and applied science. This new drive will advance knowledge in a field which heretofore has been investigated for its own sake or for application to the problems of the Pleistocene. The construction of roads, airfields, and other facilities gives rise to problems new to American engineers and construction men. The extensive experience and studies by the Russians in Siberia have been summarized in the excellent manual by Muller.¹ New studies have recently been undertaken in Alaska by the U. S. Geological Survey and by the U. S. Engineers. This economic interest reinforces and adds a drive which means progress in the study of intensive frost-action and permanently frozen ground.

It appears that a new sub-science is being created and that it deserves a name. "Cryopedology" is proposed . . . as a suitable name, being derived from krúos,

icy cold, pedon, ground or soil, and logos, knowledge. The Greek root "cryo" is familiar in the words cryolite and cryogenic and "pedon" in Pedology, or Soil Science.

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In the remainder of this paper the various processes and phenomena of Cryopedology are reviewed and a set of terms is proposed. The terms should be general in import and allow the retention of local and special terms. So far as new varieties are discoverable, new names may hereafter prove necessary. Local words with local connotations are so useful, particularly in reports of an economic import, that many of these terms should be retained as synonyms. The new terms are compounded so far as possible from familiar roots already established in English usage. They will, therefore, be readily converted into other European languages.

NEED FOR GENERAL TERMS

Frost-action as a term involves a variety of processes and implied results. There are the phenomena of freezing. . . . The onset of low temperatures freezes the water in the pores of the ground but there is little resulting expansion. In a body of ground provided with capillary pores and connected to unfrozen water-bearing ground, ice continues to crystallize in layers and masses. Expansion of the frozen layer ensues and results in thrusts in all directions. As the direction of easiest relief of strain is upward, expansion of the ground in that direction is notable and is usually called frost-heave. However, the upward expansion is frequently highly concentrated at spots having the best capillary connections to the best water-supply. There is no common expression for the lateral thrust resulting from expansion although horizontal as contrasted with vertical frost-thrust would sufficiently carry the meaning. . . .

However, the thawing of frozen ground induces new movements. The frozen ground usually contains ice to a volume much greater than the volume of pore space. On melting, the grains are separated from each other by films of water and the mass lacks coherence. There results differential and mass flow. Our present knowledge is insufficient to describe all the intricacies of this flow. The objective of many students is to analyze the movements completely. It is certain, however, that if the melt-water can escape, much fine-grained material is carried off. Further, the body of melted ground is rearranged by differential movement and, if a gradient exists, there is also a mass flow down-slope.

These movements may be arrested by a new freezing cycle, and obviously the number of alternations from freezing to melting and their duration and intensity affect the movements. Further, every cold period is accompanied by evaporation of water and ice. The surface of the ground becomes loose and pulverulent. This dry layer also modifies movements on later melting.

The mass movement down-slope was named by Andersson² "solifluc-tion" (from solum, soil, and fluere, to flow). His term, not being strictly limited to flow under conditions of freeze and thaw, has been extended to cover soil flow under other conditions. Salomon-Calvin³, who restricts solifluction to motion over a base of permanently frozen ground, points out that those who use solifluction as synonymous with "soil flow" need another expression for the process described by Andersson. This new term is here suggested.

Furthermore, the movements of material under severe freezing and thawing are not confined to simple mass flow but are more complex. Fine-grained materials are winnowed out so that the surface layer is coarser than the base. Also, the coarse and fine components of the surface layer move differentially so as to produce the much studied and highly varied "soil structures."

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What can be proved easily is that the surface layer, 1 to 3 feet thick and in places as much as 10 feet thick, has been disturbed and that some of its components have been translated down-slope. The nomenclature here proposed emphasizes the disturbance rather than the fact or the method of down-slope movement.

In summation, the easily ascertained effects of intensive frost-action can be assigned to two groups of related processes: (1) the break-up of rock by freezing of water, a familiar process; (2) the differential and down-slope movement of the surface layer. The latter process, although it has been the subject of many studies over the past thirty years and in spite of the pursuit of these studies at an accelerated rate, is still not well understood. Most of the difficulties in nomenclature are in this field of effort. . . .

TERMS FOR FROST-SPLITTING

The break-up of rock by freezing normally requires repeated freezing with intervals of thawing and results in the production of rock spalls and also in the comminution of rock into small grains. These phenomena are referred to as "frost-splitting" or "frost-riving," and the fragments are said to be "frost-split" or "frost-riven." These are good English expressions and unobjectionable. They are paralleled by the German, Frostsprengung and Spaltenfrost. The slim crystals of ice which form at right angles to the ground surface are called needle ice, and in German, Pipkrake. However, no word is available for the product of frost-splitting either as individual pieces or as a mass. . . .

In compounding a new term, the obvious root is derived from Latin gelo, gelare, to freeze, and gelu, frost. There are many derivations in English, most of which refer to the formation of a jelly from a liquid, as gelatine, gelatinize, and so on. However, "gelation" means to cool from a molten state and "regelation" is familiar as the process of re-freezing of ice under pressure. The Latin, congelare,to freeze, is familiar in the word congeal, derived through the French, and the prefix con blurs the sound of gel (i) so that the compound becomes distinctive.

Thus for frost-splitting the word congelifraction is proposed from congelare to freeze and fractare, to break. There is then available the noun "congelifract" for the individual fragment produced. If the con-gelifracts are large, the body or heap of fragments, or "spalls," is a rubble of congelifraction. But there are many kinds of rubble, and precision is necessary if one is to distinguish between heaps of rubble produced by simple gravitational accumulation in a warm desert, and the rub-bles of talus in a cool mountain area where most of the rock spalls are "congelifracts." Further, the comminution of rock into mineral grains by frost-action produces a distinct type of sand and finer fragments. Both large and small congelifracts would form bodies of material to be designated by the term "congelifractate."

TERMS FOR MOVEMENT UNDER FROST-ACTION

As previously pointed out, the term solifluction is no longer strictly confined to flow under freeze and thaw.⁴ A. Heim⁵, for instance has introduced "subsolifluction" for the flow and sliding of soft materials under sublacustrine and submarine conditions.

However, some authors . . . not only use solifluction for the process but also for the product. Such usage may be justified in French grammar, but is not to be excused in English. Nor can the spelling "soliflu-xion" common in the writings of English authors be strongly defended. . . .

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It is obvious that a word is needed for the process and for the result. A recent coinage by Edelman, Florshutz and Jeswiet (1936) is "cryoturbation" which has been adopted by Cailleux (1942). The word is derived from the Greek

icy cold or frost and to trouble, confuse, or stir up. The root "cryo" is familiar but there are no derivatives of the verb, although its equivalent, the cognate Latin turbare, is represented in turbine and other words.

An equivalent word can be compounded from the Latin congelare, to freeze, with turbare, to stir up, to produce "congeliturbation." The product of the process of congeliturbation is a congeliturbate. That all varieties of ground moved by frost-action are moved differentially seems established. Thus, all are stirred up or disturbed. Therefore, congeli-turbation and congeliturbate should include all varieties of process and all resulting materials.

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The down-slope movement of the congeliturbate produces a drag on materials below, resulting in "drag folds" involving the underlying material and the congeliturbate. Such plications are referred to by some English authors as the "underplight" (Dines et al.1940). However, the neutral and descriptive term "plication" seems adequate and is also applicable to those instances in which the "drag" phenomena involve only the congeliturbate.

The movement of fine-grained materials, mostly the finer products of congelifraction, to the surface is a significant part of congeliturba-tion. It is essential to the theories of formation of soil structures set forth by Eakin (1916), Högbom (1913), Gripp and Simon (1933–34), and others. This fine material is washed down-slope in the yearly period of melting in streams or sheets of water or it may flow as mud. Taber (1943), Poser (1931), and others make much of this process. Insofar as the material flows as mud the process is included in soli-fluction. The English terms, "sludging" for the process and "slud" for the material, are neither euphonious nor necessary as such material can be referred to as a congeliturbate transported by solifluction or by sheet-wash as the facts indicate.

TERMS ASSOCIATED WITH PERMANENTLY FROZEN GROUND

. . . The terms "perennially frozen ground" and "perpetually frozen ground" are . . . awkward; the equivalent German and Russian is equally difficult. . . . Muller, in his useful review and analysis of Russian studies of the Arctic, has sought the obvious convenience of a single word for permanently frozen ground by coining "permafrost."

"Permafrost" has the merit of being euphonious, but it is an etymological monstrosity, made by contracting "permanent" (through French from Latin, permanere) and combining it with the English word "frost," none of whose meanings refer to the ground. It sounds like a trade name for a refrigerator, and "permaform" and "permalift" actually exist as the trade names of types of brassieres. There is also a glue named "permacel." These slight crimes might be forgiven, but it is impossible to make a verb or a verbal noun from "permafrost," as "perma-frosting" and "permafrosted" imply that a permanent surface or coating has been applied. Hence the act of producing permanently frozen ground cannot be expressed. Further, the term cannot be easily converted into other European languages.

These various objections can be met by a new term which, being compounded from Latin roots already established in English usage, would convey a meaning on its face. Such a word is "pergelisol" from per = throughout or continuing + geli = gelare,to freeze + sol, from solum,the soil or ground. In this term the use of the prefix "per" blurs the resemblance to gelatine and other derivatives of gelare with the connotation of jelly.

The several modifications and attributes of the permanently frozen ground pointed out by Muller can then be easily made: "subgelisol," "supragelisol," and "dry pergelisol."

One of the great problems of the Arctic is the time and manner of formation of the pergelisol. To what extent is the area now occupied strictly in accordance with modern climate? Johnstone (1930) has recorded frozen ground at depths of 30 feet below the surface and thus obviously below the depth of present-day freeze and thaw. It must be fossil. The question is thus raised as to what extent part of the pergeli-sol may be residual from the colder climate of the Pleistocene? The great areas of congeliturbates in periglacial areas imply that pergelisol was also present. Thus future discussion will involve again and again the process of formation of pergelisol. It is suggested that the term "pergelation" be adopted, a word strictly analogous to "regelation," already a familiar term in glaciology. Muller¹ uses "aggradation of permafrost" in the sense of pergelation as here proposed. For the thawing of pergelisol by natural or artificial means he uses "degradation of the permafrost" an idea which can easily be carried by de-pergelation.

Above the pergelisol lies a layer which thaws each summer and freezes each winter to a degree dependent on the march of temperature and the duration of the seasons. In this layer "frost-action" takes place, and hence Muller calls it the "active layer." As thawing cannot occur without previous freezing, it is useless to argue as to which produces the greatest part of the activity involved. The annual thawing of this layer is its prime characteristic and it is consistent that the terminology emphasize this distinction from the pergelisol. In thawing there is usually produced more water than the volume of pore space so that the layer becomes soft and tends to flow. It may therefore be termed the "mollisol" from L. mollere, to make softer, pliable, to melt, and sol = solum. The root of this word is familiar in "emollient" and other words. The act of thawing and softening may, if desirable, be known as "mollition."

The softening of the mollisol is its major characteristic although in well-drained ground where dry pergelisol occurs, melting produces no apparent softening. Whether such areas are large is not known and thus it is at present impossible to evaluate dry pergelisol. However, softening, or "mollition," is the common activity and sets in motion the forces which result in congeliturbation. A fossil mollisol is a con-geliturbate.

Muller points out that cool or short summers or very cold, long winters lead to failure to melt all the ground frozen the winter before. There thus intervenes between the mollisol and the pergelisol a layer of frozen ground which may persist for one or several years. For this layer he uses the Russian term "perelétok." Offhand there is no objection to adopting this Russian word but the pronunciation, which can be expressed more or less accurately by "pjerelyétok," is difficult. However, by the use of the prefix inter, among, between or amid, one can coin "intergelisol," which gives a term that will sufficiently express the likeness of this material to pergelisol and also its situation between the top of the pergelisol and the mollisol.

Muller also introduces the Siberian word "talik" for bodies of unfrozen ground above, within, or below the pergelisol. This word has the merit of shortness and has only the handicap that it cannot easily be made into a verb. It appears that for various causes these areas of unfrozen ground are formed and again are refrozen. The production of "talik" is an idea that will doubtless be discussed and for which a

Fig. 4. Diagram showing terminology proposed: A. characteristic parts of the ground in areas of permanently frozen ground; B. characteristic parts of the ground in periglacial areas.

term appears to be desirable. The new term "tabetisol" is here suggested from L. tabescere, to melt, and sol = solum. The root is present in English in "tabes," a wasting disease, and "tabetic," wasting, which is symptomatic of tabes. The production of tabetisol would be expressed by the verb to "tabificate" and the verbal noun "tabification."

The proposed terminology is parallel for present-day areas of intensive frost-action and for areas where this process was current in the past. The terminology is summarized in Fig. 4.

WIDESPREAD EROSION BY FROST-ACTION

The idea that landscape can be molded by frost-action and that widespread and extensive reduction of elevation may occur in areas where frost-action is the dominant process is an old one. . . .

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. . . In Arctic and high mountain lands, reduction of the land may be largely due to intensive frost-action and concurrent action. Furthermore, similar processes were once at work in the periglacial region. . . . The land forms are not analyzable under the normal "Cycle of Erosion" of Davis. A new term seems necessary, and an appropriate coinage would be "cryoplanation," from

icy cold or ice, and plane, through French from L. planus, Greek, broad. The term would be parallel to peneplanation although without implication that the process had reached or nearly reached completion. We would, however, be able to say that an area is or has been subject to the "Cycle of Cryo-planation" in contrast to areas subject to the "Pluvial-fluvial Cycle."

^* From American Journal of Science 244 (1946), 622–642.

¹ S. W. Muller, Military Intelligence Division, U. S. Army, Strategic Engineering Study No. 62, 1945.

² J. A. Andersson, J. Geol. 14 (1906), 91–112.

³ Wilhem Salomon, Heidelberger Akadamie der Wissenschaften, Sitzberg. Jahrgang, 1929 (Berlin and Leipzig).

⁴ C. F. S. Sharpe, Landslides and Related Phenomena, Columbia University Press, 1938.

⁵ Arnold Heim, Neues Jahrb. Mineral Geol. Palaentol. 2(1908), 136–157.