The following is an editorial first published in Frozen Ground in December 2002 by Hugh French. Because the use of melt is now so widespread and not necessarily adequately used, we thought we would publish it again here.

THAW VS MELT: AN EDITORIAL (FROZEN GROUND, DECEMBER 2002)

Hugh French
University of Ottawa
Canada

For many years the English-speaking permafrost community has seen the need to standardize terminology. In the early 1980’s, the Associate Committee on Geotechnical Research (ACGR) of the National Research Council of Canada established a Terminology Working Group to update the earlier ‘Permafrost Terminology’ volume first developed by R. J. E. Brown and W. O. Kupsch (1974). The result was the widely used ‘Glossary of Permafrost and Related Ground Ice Terms’ (ACGR, 1988). This was followed by the IPA-sponsored ‘Multi-language glossary of permafrost and related ground-ice terms’, in 12 languages (van Everdingen, 1998). This volume also includes a list of definitions, references, and illustrations, many of which had appeared in the 1988 publication.

In all publications there are numerous terms that include the word ‘thaw’. However, ‘melt’ is a commonly used synonym in both the scientific and popular literature. For example, it is common to refer to ‘melting permafrost’, where the word ‘melt’ is used in an adjectival sense, or to state that ‘permafrost is melting’ where the word is used as a gerund (e.g. Earth Observatory News, December 10, 2001; The National Post, November 14, 2002). Today, the potential impact of global warming upon the distribution of permafrost necessitates that a clear distinction be made in the permafrost literature between the words ‘thaw’ and ‘melt’. I believe the term ‘permafrost melting’ is incorrect or, at best, imprecise language. Moreover, and equally unfortunate, there is a degree of overlap of meaning attached to these two words if one consults the Oxford English Dictionary, the Collins English Dictionary, or others.

I recommend that the term ‘thaw’ be used when soil and/or rock becomes either warmer or passes to an unfrozen state. The alternative term is ‘degrade’, as in ‘permafrost degradation’ or ‘permafrost aggradation’. By contrast, the term ‘melt’ should be used only when there is a change from a solid to a liquid state. Thus, although permafrost can degrade and its temperature will change, its physical state may, or may not, change. This often depends upon the degree of consolidation of the soil or rock. However, the critical issue from the terminological perspective is whether the permafrost is ice-bearing or ice-bonded, i.e. the amount of ice present in the permafrost. Therefore, it seems appropriate to refer to the ‘thaw’ of soil and/or rock when referring to permafrost degradation but to the ‘melt’ of any ground ice contained within the permafrost. For example, it is more appropriate to refer to the ‘thaw’ of ice-rich permafrost and the ‘melt’ of massive ground ice. Likewise, it is more appropriate to refer to the ‘thaw’ of the active layer than to its ‘melt’. In the case of a collapsing pingo, one might refer to the ‘thaw’ of the overburden and the ‘melt’ of the ice core.

The frozen and/or unfrozen state of water within permafrost and the associated terminological problems are central to this discussion. The distinction between the thermal and physical state of permafrost, first highlighted by van Everdingen (1978), is relevant to the definition of the active layer (e.g. see Burn, 1999) and to monitoring programs such as CALM.

References:

Associate Committee on Geotechnical Research (ACGR), 1988. Glossary of Permafrost and Related Ground Ice Terms. Permafrost Subcommittee, National Research Council of Canada, Technical Memorandum 142.

R. J. E. Brown and W.O. Kupsch, 1974. Permafrost Terminology. Associate Committee on Geotechnical Research, National Research Council of Canada, Technical Memorandum 111.

C. R. Burn, 1999. The active layer: Two contrasting definitions. Permafrost and Periglacial Processes, 9, 411-416.
Earth Observatory News, December 10, 2001. New study shows early signals of climate change in Earth's cold regions., Media Alert Archives, NASA, Boulder, Colorado, USA. See:
http://www.colrado.edu/PublicRelations/NewsReleases/2001/1533.html

R. O. van Everdingen, 1976. Geocryological terminology. Canadian Journal of Earth Sciences, 13, 862-867.

R. O. van Everdingen (compiler and editor), 1998. Multi-language Glossary of Permafrost and Related Ground-Ice Terms. International Permafrost Association.

The National Post, Ottawa, Canada, Thursday, November 14, 2002. Kyoto: myths and science. Andrew Weaver. pA5.