Volume of Abstracts - Università degli Studi di Milano

More documents

Recommendations

Info

5 th Int. Workshop on Ice Caves (IWIC – V) Barzio (LC), Valsassina, Grigna and Milano, September 16 – 23, 2012 Volume of Abstracts rooms and passages as well as seasonal and short-term changes in the cave icing processes. ICE MASS AND FROZEN GROUND IN PERMEABLE VENTILATED SYSTEMS: COMPARISON BETWEEN A DYNAMIC ICE CAVE AND OVERCOOLED TALUS SLOPES IN WESTERN SWITZERLAND Morard S. 1 , Bochud M. 2 & Delaloye R. 1 1 Alpine Cryosphere and Geomorphology, Geography Unit, University of Fribourg, Switzerland 2 GeoAzimut Sàrl, CH-1700 Fribourg Both ice cave and talus slopes are open mediums inside which air can flow, and where ice mass and frozen ground are encountered even at location where the mean annual external air temperature (MAAT) is largely positive. Air circulation is known to be a major process determining both the cave climate and the thermal regime of ventilated talus slopes - a frequent landform in alpine and peri-alpine environments. Dynamic ice cave could be seen as a simple talus slope with one wind channel and two entrances located at different elevation. The first main objective of this presentation is to compare the ground air temperature measured inside several windholes in the lower part of talus slopes with the cave air temperature at the lower entrance of the small dynamic Diablotins ice cave. The second main objective is to present the thermal regime evolution of several low elevation talus slopes located in western Switzerland. The same thermal regime was recorded between 2009 and 2011 in the lower part of these two kinds of ventilated systems: during wintertime, cold and dry air is aspirated in the lower parts with a quite similar and synchronous thermal regime with the outside air temperature. During summertime, the short-term variations of air temperatures are almost perfectly the same between the windholes and the cave entrance, with Pearson coefficient of correlation from +0.735. Moreover a clear inverse relationship could be seen with the outside air temperature. Knowledge about heat exchange into cave system could also be extrapolated with a high degree of confidence to ventilated talus slopes. The thermal monitoring conducted at the ground surface in several low elevation talus slopes has shown that the key factor of evolution is the temperature of the outside air during winter. Periods of prolonged and very intense cold weather in winter promote a deep freezing of the ground. A part of the heat advected by the airflow is transmitted by conduction to the rock debris and the finer sediments located below the porous debris accumulation. A well-defined relationship is also recorded between the 31
5 th Int. Workshop on Ice Caves (IWIC – V) Barzio (LC), Valsassina, Grigna and Milano, September 16 – 23, 2012 Volume of Abstracts winter cooling of the talus slope and the ground thermal conditions prevailing in summertime. It may be noted that a particularly mild winter with limited freezing of the ground as in 2006/2007 causes a significant increase in ground surface temperatures during summer and fall. The growth of temperate permafrost below the porous talus slope of Dreveneuse d'en Bas has been reported in two boreholes in 2004-2006. Following the mild winter 2006-2007, this frozen ground disappeared and finally reformed in 2010 consecutively to the very cold winter 2009-2010. On the other hand the outside air temperature in summer and the thickness of snowcover contribute very modestly to changes in the thermal regime. This particular thermal behaviour significantly differs from conventional permafrost situations (eg. rock glacier) at high altitude. On the other hand, processes inside talus slope are very close from those which are encountered in the lower entrance zone of the dynamic ice cave. THE INFLUENCE OF THE ICE CAVES ON CLIMATE OF KARST DEPRESSIONS – CASE OF LOW ALTITUDE PERMAFROST AT SMREKOVA DRAGA, TRNOVSKI GOZD, SLOVENIA Mihevc A. 1 1Karst research institute ZRC SAZU, Titov trg 2, SL-6230 Postojna, Slovenia (Mihevc@zrc-sazu.si) Perennial ice in low latitude and low altitude caves, where mean air temperature on the surface is above zero, forms due to the winter air circulation and cooling of the caves. In most cases the summer circulation is less intensive and that makes the perennial ice possible. Most ice cave studies are devoted to factors of cave and surface morphology that enhance formation and duration of the cave ice. Les is known the influence of the caves, especially influence of ice caves or caves in general on the topoclimate of the karst surface, especially karst depressions. Trnovski gozd is high Dinaric karst plateau in altitude mostly between 800 – 1200 m a.s.l., only the central part to reach height 1400 m. Surface of the plateau is dissected by numerous large and deep dolines. Mean annual temperature on the plateau about 7º C, January (-3º C) is the coldest and July (13º C) is the warmest month. Besides several ice caves, the largest is Velika Paradana, there are numerous deep dolines where temperature inversion is important phenomena. This phenomenon was first studied at Velika Paradana entrance and later in Smrekova draga. Smrekova draga is about 1 km wide, and more than 150 m deep closed depression, a large composed dolina. The dolina is well known for its extreme vegetation inversion. This phenomenon was first attributed to 32
Page 2 and 3: IWIC - V 5 th INTERNATIONAL WORKSHO
Page 4: President 5 th Int. Workshop on Ice
Page 7 and 8: 5 th Int. Workshop on Ice Caves (IW
Page 13 and 14: Dear Participants, we are very plea
Page 46: POSTER PRESENTATIONS
Page 61: 5 th Int. Workshop on Ice Caves (IW

Volume of Abstracts - Università degli Studi di Milano

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?