It has been too long since I went caving. I'm going to spend this weekend down near Carlsbad participating in a cave dig at Big Manhole Cave. A bit of background for people who haven't heard me tell this story a billion times:
Caves tend to keep the air inside at a reasonably constant temperature and pressure, so when the barometric pressure outside changes, they will "breath." Winds at cave entrances can be quite strong; creatively named Wind Cave, SD, has had measured airflow at the entrance reaching 100mph. The amount of airflow a cave experiences is a function of many things, but the big ones are the volume of the cave, the rate of change in barometric pressure, and the cross sectional area of the entrance passage. In general, the faster the wind blows in the entrance, the bigger the cave.
Sometimes a seemingly small cave will blow considerably more air than it should for its known size, suggesting that there is a lot of undiscovered passage in there somewhere. A famous example of this is Lechuguilla Cave in Carlsbad Caverns National Park, which was just a 90' pit of no interest, other than the extreme winds coming out of a rubble pile at the bottom. A project started to dig there and eventually broke through into what is probably the most spectacular cave in the United States. At last survey, there are over 120 miles of passage in Lechuguilla and lots of going leads.
Anyway, Big Manhole is another cave in the area (the entrance is less than a mile from Lechuguilla) and it blows pretty fiercely sometimes too. It's possible that it is another entrance to Lech, but it could be its own large system. Currently the cave is just a 60' tall dome room about 100' in diameter. They have been digging in this cave for the better part of 20 years and no breakthrough yet.
Electroresistivity studies of Big Manhole suggest that it has some very large voids near the known chamber and that the dig tunnel is heading straight towards them. Lately, the dig tunnel has been breaking through into some small voids (big enough for a person or so) with increasing frequency. At the end of the last dig, they broke through into what looked like a bigger chamber, but it was late on the last day of the dig and people were having to leave, so they didn't enlarge the hole enough to really tell what they had. It's probably just another small void, but it could be something important.
Anyway, I'm going down this weekend along with 21 other people and we're going to see what happens when hammerdrill meets calcite.
