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Is there a Depth Limit?
Posted: Sat 06 Jan 2018 10:10
Although the thermal gradient into the centre of the earth is quite low (around 0.03C/m), how far would the penetration of permafrost change this? Has anyone modelled the simple situation of the impact of coldness on solid rock using thermal conduction? Open passage will modify this by processes which are probably too difficult to model but caves do exist in cold regions. Has anyone gathered data on the penetration of cold into a 'simple' cave system? I ask because my initial thought on one report of the possible presence of CCC was ‘surely that is too far within a cave to be effected by permafrost’.
Re: Is there a Depth Limit?
Posted: Thu 01 Feb 2018 12:04
Sorry for the delay, I only recently saw this post!
Marc Luetscher replied with the following...
Yes, simple 1D modelling of heat diffusion is straightforward (and has been done on many occasions). The issue here is to know to which extent advection affects the thermal distribution in karst systems. This implies having a rough idea of the water and air fluxes transferred through the system, which depend on the location of the karst (climate and geology) as well as on the conduit system (density, geometry). To some extent, this is site specific and the litterature shows contrasting appreciations of these fluxes, partly depending on the speleological experience of individual researchers (e.g. Luetscher and Jeannin, 2004; Covington et al. 2011).
The thermal penetration depth depends on the frequency of the signal we are considering. Whilst seasonal temperature fluctuations are usually measured within the first ca. 50 m only, Eisriesenwelt is a good example of an extreme case where the seasonal penetration depth reaches several hundreds of meters. On a glacial cycle, permafrost has typically affected depths of >1000 m. Meanwhile, the stals from 7H have shown that there might be taliks allowing for water drainage also during full glacials. So far, only few empirical data do support these models and CCCs may significantly contribute to the debate. Modelling this is, however, a real challenge as it depends on the effective recharge and the size of the conduits. I am currently working on these issues and hope to get some good results in the near future.