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Natural speleothem damage has been known from Postojnska jama for a long time. Schaffenrath was the first to depict broken and leaning stalagmites on his pictures from the interior of the cave. Hohenwart analysed some of these damages, clearly excluding rock fall or earthquakes as a cause. Here the author discusses the possibilities, which could cause natural speleothem breakage in general. The most promising cause is cave ice. It must have formed in caves during glacial maxima when permafrost spread throughout northern, eastern and central Europe. Consequently cave ice could be the most prominent factor in explaining non-recent speleothem damage. Next some of the historically known flowstone breakages from Postojnska jama are presented. These are discussed in view of cave ice and an ad hoc model for the genesis is given. In the side passages Pisani rov and Brezimenski rov there are masses of broken stalagmites and stalactites and speleothem fragments in precarious positions. Cave ice offers an overall process to explain these observations. Thus it is suggested that all or parts of the Postojnska jama were filled with ice during the Last and earlier Glacials. If accepting speleothem damage as a consequence of glacial cave ice, then it should be possible to use it as a marker facies for the extent of the zero temperature line during the various glacials.
The important regional thrust called Snežnik thrust, that divides the Snežnik thrust sheet from the parautochthon of the Komen thrust sheet, runs through the Pivka basin. A tectonic window near Knežak is proof of older thrusting deformations. The landscape is cut by numerous younger faults among which the most important are Raša, Predjama and Selce faults. The area of Upper Pivka is tectonically quite active, which is shown by earthquakes in recent years. It looks as if the most active is the Raša fault or one of its northern parallel faults, for example Šembije fault or maybe Selce fault. Karst intermittent lakes of Upper Pivka are developed in Upper Cretaceous limestones. The lakes are situated 0.5-4.0 km NE from the Snežnik thrust. Most of the lakes are situated along the Selce fault.
Migrating regional ground water divides can create unstable zones of relatively stagnant flow in upland areas. Unlike traditional upland ground water divides, the process of flow reversal causes these zones to reject recharge. Artesian pressure surfaces limit the downward infiltration of precipitation and form the subenvelope above which ground water sapping can create a ‘peneplain’ (Stearns, 1967). Only regolith and rock above the pressure surface subenvelope is available for epigenic erosion. Inertia is eventually overcome and ground water circulation substantially increases as hydraulically-advantaged, ‘entrenched’ river systems capture the isolated packets of stagnant ground water. As artesian pressure is lost in the upper story, losing streams form. The losing streams may eventually be consumed by the steep slopes of an entrenching stream, thus completing the reversal of flow. Water level data suggest that the dewatering of stagnant divide areas can be hastened by distant earthquakes.
A variety of observations in Missouri, including recent studies using heat pulse flow meters, show that pressurized sandstone aquifers are widespread beneath upland divides and at surprisingly high elevations. The ground water in the sandstones is confined by relatively tight carbonates. Ground water leaves these confined aquifers by slowly percolating upward through the confining carbonate into shallow bedrock fractures. Storm events then flush shallow mineral-laden ground water into surface streams, which is why floodwaters tend to be dominated by ground water (Frederickson & Criss, 1999). In the major valleys, transverse speleogenesis reverses the hydraulic role of the carbonate beds (Klimchouk, 2003). Classic artesian hydrology generally ignores these mechanisms and cannot explain why most large Ozark caves are associated with sandstones. Unlike classic artesian systems, artesian aquifers in the Ozarks typically lack a marginal recharge zone. Artesian pressures are maintained by ongoing vertical movements. A subsidence rate of approximately 1 mm/yr in the Northern Mississippi Embayment (Calais, 2008) would cause the Ozark ground water divide to migrate to the north and west at approximately 0.7 meter per year, assuming a constant gradient. Flat interfluve summits form as the flow reversal process unfolds.
Once thought to be remnants of ancient peneplains formed near sea-level, isotopic evidence now indicates that modern Ozark summits are actually being sapped by relatively shallow but significant zones of chemical migration. The flat summit surfaces and the steep stream valleys form simultaneously as the landscape is lowered and drainages are rearranged. There is no need to postulate the prior existence of a low elevation peneplain. The uppermost artesian pressure surface acts as the base level, not sea level. Flat interfluve surfaces can form at any elevation, depending on hydrologic conditions. The summit surfaces appear flat because they are essentially created by a regional ground water surface that is widespread and relatively flat.
The present publication focuses on the study of caves in northern and central Switzerland in order to detect and date historical earthquakes and active tectonic displacements by investigations of broken and resealed or displaced speleothems datable by U/Th and 14C. While it can be shown that these methods are potentially suitable, the ages obtained are often beyond the range of historically recorded earthquakes, and it cannot be proved that the observed and dated events are related to a seismic event. Particularly this is true for the caves in central Switzerland, where most ages in the Melchsee-Frutt region were beyond the limits of the U/Th method, or of late Pleistocene age in the Siebenhengste-Hohgant region. A direct comparison with known historical (or prehistoric) earthquakes was not possible. In contrast to central Switzerland, the results in the Basle region of northern Switzerland indicates cave and speleothem damages in one cave within the epicentral area of the 1356 Basle earthquake. 14C datings allowed to directly relate the speleothem damages to this M 6.5 earthquake. Further dating results from caves in northern Switzerland on speleothems and organic material in cave deposits supplied ages which indicate older events not related to the historical Basle earthquake. The detection of active fault displacements and prehistoric strong earthquakes can only be achieved by a very careful deciphering of the palaeo-environmental records and many more age determinations which allow to separate active tectonic displacements and seismic events from other events not related to tectonics, i.e. glaciations, creep of sediments, catastrophic floods etc.
During heavy rainfalls between September 17 and 19, 2010 large part of Slovenia has suffered extensive floods that last for nearly two weeks. For the river Iška record discharge of 59.3 m3/s was measured on September 19 on the gauging station in Iška vas located at the southern rim of Ljubljansko barje. In the first hour of September 21, 2010 two weak earthquakes (ML=0.6 and ML=0.2) occurred within one minute near Iška vas. They were felt by some inhabitants who reported also a rumbling noise (brontides). During the flood recession period, the water of river Iška started to sink into the gravely stream bed or rocky left banks and the gauging profile completely dried on September 23, day and a half after the first earthquake. Water reappeared again on September 25. In the period September 21 − October 4 additional seven weak earthquakes occurred in the same area. All earthquakes from this series occurred at or near the surface and deviate in hypocentral depth from the seismicity pattern characteristic for the southern rim of Ljubljansko barje, which was analysed for comparison. The epicentres of the first two earthquakes are in good agreement with the location of the dried river bed. It is therefore probable that both phenomena are related. Analyses of seismograms have shown that it is not likely that the observed events are collapse earthquakes, but they are tectonic events. Although earthquakes were relatively weak, it seems that they could be accompanied by small near-surface tectonic movements, because they occurred at the position of a known fault. These movements are probably connected to the opening of pre-existing fissures in the karstified valley bottom, although the primary reason for sinking of the river is that high waters removed the clogged river bed that enables intensive sinking into the river bottom during the flood.
During heavy rainfalls between September 17 and 19, 2010 large part of Slovenia has suffered extensive floods that last for nearly two weeks. For the river Iška record discharge of 59.3 m3/s was measured on September 19 on the gauging station in Iška vas located at the southern rim of Ljubljansko barje. In the first hour of September 21, 2010 two weak earthquakes (ML=0.6 and ML=0.2) occurred within one minute near Iška vas. They were felt by some inhabitants who reported also a rumbling noise (brontides). During the flood recession period, the water of river Iška started to sink into the gravely stream bed or rocky left banks and the gauging profile completely dried on September 23, day and a half after the first earthquake. Water reappeared again on September 25. In the period September 21 − October 4 additional seven weak earthquakes occurred in the same area. All earthquakes from this series occurred at or near the surface and deviate in hypocentral depth from the seismicity pattern characteristic for the southern rim of Ljubljansko barje, which was analysed for comparison. The epicentres of the first two earthquakes are in good agreement with the location of the dried river bed. It is therefore probable that both phenomena are related. Analyses of seismograms have shown that it is not likely that the observed events are collapse earthquakes, but they are tectonic events. Although earthquakes were relatively weak, it seems that they could be accompanied by small near-surface tectonic movements, because they occurred at the position of a known fault. These movements are probably connected to the opening of pre-existing fissures in the karstified valley bottom, although the primary reason for sinking of the river is that high waters removed the clogged river bed that enables intensive sinking into the river bottom during the flood.
A series of sinkholes collapsed at Jili village and Shanbei village, Laibin Guangxi, China in June 2010. A large underground stream exists in the north-south transect of the study area and passes the collapse site. Preliminary investigations revealed that extremely heavy rainfall between May 31 and June 1 2010 may have triggered this collapse event. The precipitation, as high as 469.8 mm within one day, was a record high in the study area. A long period of drought in 2009 followed by extremely heavy rainfall along with cave roof collapse may have caused the collapse event on June 3 2010. The “water hammer” effect and collapse-triggered earthquakes caused severe ground failure and fractures in residential houses and Jili Dam. Several collapse events were caused by extreme weather conditions in Guangxi over the past few years. Further studies of the relationship between extreme weather events and sinkhole collapses will help minimize the damage or impact to human infrastructure by avoiding areas susceptible to collapse or by designing infrastructure to better withstand subsidence
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