Cave wind

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The air movement in a cave is referred to as cave wind or ventilation . There are essentially three causes for this air movement: temperature differences ( convective ), air pressure differences ( barometric ) and movement impulses ( mechanical ). These three mechanisms can occur together and their effects overlap.

In caves with only one entrance, the air flow is relatively weak compared to "wind tubes" with several entrances. The cave wind affects the entry and spread of material in the cave. It influences biological processes such as the formation of bacteria and, by means of wind erosion, the cave ice.

The barometric air circulation occurs when the air pressure of the earth's atmosphere changes depending on the weather . Then air is pushed into the cave through the cave entrances (atmospheric overpressure) or pushed out of the cave (atmospheric negative pressure). This wind can be very violent in some caves, but is usually short-lived (a few minutes to hours).

The convective air circulation is triggered by temperature differences, as they occur in the atmosphere due to seasonal changes or weather changes, while the temperature inside the cave is almost constant. In summer the air in the cave is colder than outside and therefore has a higher density, which leads to a downward wind with multiple entrances, while this is the other way around in winter. An entrance that blows out in summer is referred to as "meteo low", entrances that blow out in winter as "meteo high".

Impulse air movement occurs when the air is driven by movement within the cave, such as people or cave rivers. These are mostly small-scale, for example near a waterfall.

Holes in the ground, in which a wind can at least occasionally be felt, were often given the name wind hole, wind cave or weather hole. In their surroundings there is, among other things, sparse vegetation because of the cooler temperature in summer. Similar to ice caves , they were used for food preservation , for example . A cave entrance with a permanent draft is always connected to another entrance. Fundamental properties of the cave can be estimated from the cave wind, such as the cave-climatically effective air volume of the cave system, the height of the cave entrances or the question of how the narrow point at the entrance influences the cave wind.

Man-made

The same applies to man-made tunnels, tunnels and shafts. Sufficiently short tunnels are blown through by the incoming wind from outside. Another drive can be rail or road traffic passing through, especially in the case of one-way operation in the tube.

Longer tunnels work differently. Here the flow resistance of the draft becomes relevant and the mountain face is increasingly exchanging heat with the interior air.

Tunnels with only a small difference in height between the two portals are typically built with a high point inside and two inclines towards the portals to ensure that the mountain water can drain independently even in the event of a sudden water ingress. If it is significantly colder outdoors than in the mountains, warm, i.e. light air can block the passage in such a tunnel. The tunnel then acts like an inverted siphon .

In mines, the air circulation is controlled by means of active ventilation with the aim of maintaining breathable, not too hot and non-flammable air conditions. Longer tunnels are now equipped with electrically operated longitudinal and transverse ventilation and exhaust air shafts leading up through the mountain, also in order to discharge fire gases and smoke in the event of fire, as well as lockable escape routes. Tunnel construction sites are already being ventilated to remove exhaust gases from construction machinery with combustion engines and blasting.

Individual evidence

  1. ^ A b Marco Filipponi: Air movements in caves . Arbeitsgemeinschaft Höhle und Karst Grabenstetten, annual booklet 2005, pp. 121–128.
  2. ^ A b Heinrich Mrkos: The cave climate . In: Speleology in Austria. - Publications from the Natural History Museum Vienna, series 17: 40–46.
  3. ^ Marco Filipponi: Air movements in caves . Arbeitsgemeinschaft Höhle und Karst Grabenstetten, annual booklet 2005, p. 122.
  4. ^ Benjamin Menne, Gerhard Rückert: Myxobacteria (Myxobacterales) in cave sediments of the Hagen Mountains (Northern Limestone Alps). In: Die Höhle , 39th year, No. 4, 1988. pp. 120-131.
  5. ↑ Trimmel, Hubert. "Geospeleology." Caving. Vieweg + Teubner Verlag, 1968. 6-103.
  6. ^ Marco Filipponi: Air movements in caves . Arbeitsgemeinschaft Höhle und Karst Grabenstetten, annual booklet 2005, p. 123.
  7. ↑ Marco Filipponi: The climate of the Schrattenhöhle . P. 10.
  8. ^ Cave climatology , Arbeitsgemeinschaft Höhle und Karst Grabenstetten, accessed on August 26, 2014.
  9. ^ A b Marco Filipponi: Air movements in caves . Arbeitsgemeinschaft Höhle und Karst Grabenstetten, annual booklet 2005, p. 124.
  10. ↑ Weather hole, that . Adelung, Grammatical-Critical Dictionary of High German Dialect, Volume 4. Leipzig 1801, p. 1514.
  11. ↑ Windhole, that . Adelung, Grammatical-Critical Dictionary of High German Dialect, Volume 4. Leipzig 1801, p. 1558.
  12. ↑ Ferdinand Keller: Comments on the weather holes and natural ice grottoes in the Swiss Alps . Natural Research Society in Zurich , 1839.