NPS Photo by Bridget Litten.
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Climate conditions in Carlsbad Cavern are an exception to the average cave. With a large entrance and many miles of passages that drop over 1000 feet, climate conditions in the cave are very complex and only remain fairly stable long distances from the entrance. The main portion of the cave is a cold trap. In winter, once the temperature outside has dropped below the temperature in the cave, cold, usually dry, air plunges into the lower part of the entrance. This cold dry air flows down the large Main Corridor and into the Big Room and Lower Cave. As this cold dry air pushes into the cave along the floor, warmer moist air is displaced, forced up to the ceiling and pushed out of the upper part of the entrance. Over a long period of time, this natural process has cooled the Big Room to an average of 56°F, which is 12°F cooler than the ends of the cave and other large cave systems in the area. This influx of cold dry air is a natural drying process that changes the relative humidity in significant parts of the cave as well. Relative humidity drops to as low as 87.5% in the Big Room during winter months and remains at about 100% during the summer months when there is less airflow exchange from the entrance.
Tthe climate at the deepest point in Carlsbad Cavern-at 1,034 feet-is less affected by this process. Because of its depth and distance from the entrance, this lowest point remains a more constant and warmer 68°F and closer to 100% relative humidity.
The climate conditions within Lechuguilla Cave, also within park boundaries, are significantly different than those in Carlsbad Cavern because it is an extremely large and deep cave (over 121 miles long and the deepest limestone cave in the United States at 1,604 feet deep) with only one very small entrance. While the cave itself has a very complex wind system due to barometric pressure changes on the surface, the influence from surface conditions at the entrance to most of the cave is small. Temperature and relative humidity reach fairly stable conditions a short distance into the cave. The average temperature throughout the cave is also 68°F and the relative humidity remains close to a constant 100%. Lechuguilla Cave is such a large cave system and the climate conditions portray some subtle variations that cannot easily be explained. Though more subtle than climate variations in Carlsbad Cavern, these are only now being recognized and studied.