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The problems concerning the development of show caves are here considered by taking into account different aspects of the problem. A procedure to carry out an Environmental Impact Assessment (EIA) has been established in the last decade and it is now currently applied. Such an assessment starts with a pre-operational phase to obtain sufficient information on the undisturbed status of a cave to be developed into a show cave. Successively a programme for its development is established with the scope to optimise the intervention on the cave at the condition that its basic environmental parameters are not irreversibly modified. The last phase of the assessment is focussed to assure a feedback through a monitoring network in order to detect any unforeseen difference or anomaly between the project and the effective situation achieved after the cave development. Some data on some of the most important show caves in the world are reported and a tentative evaluation of the economy in connection with the show caves business is eventually made.

The physical characteristics of radon are reported as well as its sources,the transport in rock and its behaviour in caves. Then, the instruments,both active and passive, used for the measurement of radon concentration are discussed by taking into account their respective advantages and disadvantages for the use in the cave environment. Since in many countries radon is the object of regulations that were adopted for radiation protection purposes, this aspect is examined and the recommendations issued by international organisations and enforced in different countries are reported. Materials, methods and other remarks on the limits implementation are also listed with the aim of providing the managers of show caves with some instruments to comply with the domestic requirements with the most convenient solution.

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In the past some authors described the speleogenetic role of convection in phreatic conditions. Similar effects exist also in the air-filled part of vadose passages of caves as a consequence of an air circulation due to a relevant temperature gradient; the effects can be enhanced by the presence of some acids as, e.g., H2S, H2S04, etc. In this paper the conditions matching convection and condensation which produce typical forms, very similar to those found under phreatic conditions, are discussed both for limestone and gypsum caves. RIASSUNTOIn passato vari autori han no descritto il ruolo speleogenerico di fenomeni convettivi in regime freatico. Effetti analoghi si verificano anche nelle zone emerse di livelli vadosi in conseguenza di una circolazione d' aria provocata dalla presenza di notevoli gradienti termici in atmosfera; questi effetti possono essere esaltati dalla presenza di acidi come, per esempio, H2S, H2S04, ecc. In questo lavoro vengono prese in considerazione, sia per grotte nel calcare che nei gessi, Ie condizioni che possono ponare a convenzione e condensazione provocando COS! forme molto simili a quelle che si riscontrano in condizioni freatiche.

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