J E W E L   C A V E   N A T I O N A L   M O N U M E N T

Southwestern South Dakota

The surrounding rock was quite colorful.

We finally arrive at the cave entrance. While standing in front of the entrance, we're all hit by a strong, cold wind draft that's eminating from the cave. The guide goes on to explain the draft is a result of air pressure differential. The draft happens to be exiting the cave's entrance because the pressure in the cave is higher than the pressure outside the cave. The reverse draft is possible when the outside pressure exceeds the inside cave pressure. It's quite amazing, how pressure differential can cause such a phenomenon.

The guide tells us the size of Jewel Cave can be measured by the volume of air the cave inhales and exhales. It's been estimated that the cave's passageways have a total capacity of 5 billion cubic feet. That boils down to a 16 by 16 foot tunnel 5,000 miles long. Hard to believe. The reality is the vast majority of the cave will never be explored because of the diminishing returns of exploration. To get to the furthest reaches of the cave, one has to travel 11 hours.

The opening itself is gated for obvious reasons, to keep the human animals out. When the cave was discovered, this opening was smaller than a basketball. It was discovered when someone noticed cold air exhausting from the opening. They widened the opening and that was the start of the cave's exploration. At present there are more than 132 miles of passages that have been surveyed, making it the 3rd largest surveyed cave in the world.

The cave is mostly an amalgamation of large and small passageways. There are some large "rooms" however, the largest is a whopping 600 feet long by 150 feet wide by 150 feet tall. Now that's pretty big! Unfortunately, it takes about 10 hours of cave trekking to get to it.