File:Breeze from Mammoth Cave's Historic Entrance (Kentucky, USA) 2 (37792234112).jpg

This early summer 2011 video clip shows vegetation downhill from Mammoth Cave's Historic Entrance in western Kentucky. The noticeable breeze is not from atmospheric winds, but from airflow exiting the mouth of the cave.

From park signage: "If you are here on a warm day, you probably feel cool air blowing out of the cave. The rate of this airflow influences cave temperatures, which in turn affect underground habitats for creatures such as bats.

Human activity over the last 180 years has altered the natural airflow - the entry passage was gradually cleared of rock, and a series of gates alternately restricted and later allowed excessive flow of air.

Steps have been taken to restore the air exchange rate. This will provide proper hibernation temperatures, and encourage the recolonization of bats and other creatures. The only way to find out what hibernation temperatures should be is to study bat bones discovered in the cave. Bats hibernate within very precise temperature ranges, so discovering what kinds of bats once lived in the cave will tell us what the temperature once was.

Summer Airflow 1) Hot surface air expands, becoming less dense, which allows relatively cooler, denser cave air to pour out through lower cave entrances.

2) A partial vacuum is created in the cave. Deep cave temperatures remain between 55 and 57 degrees Fahrenheit year-round.

3) Fresh air is drawn down through higher entrances to replace the exiting air.

Winter Airflow 1) Warm cave air rises upward through denser surface air. These upwellings may be visible as plumes of steam.

2) A partial vacuum is created in the cave