12 July 2025 – Data logger service trip

Time in = 9:30am, Time Out = 3:15pm

Participants – Bill Gee (trip leader)
Marty Griffin
Mike Kovacs
Josh White
Peter Schnegelberger
Jessica Wilson

Trip report by Bill Gee

Twice a year I visit Carroll Cave to collect data from the data loggers. We have six data loggers. There is a rain gauge on the silo. Five more loggers in the cave collect barometric pressure data and four locations for water depth. All of the loggers also record temperature.

The loggers collect a data point every 30 minutes. At that rate their memory fills up in about 7 months. Visiting them twice per year ensures that a full year of data is collected.

I picked up Josh White at his house early in the morning for a carpool ride to Carroll Cave. We arrived at the silo at 8:00am. Peter and Jessica were already there. My first task was to change the battery in the rain gauge logger. This requires restarting the logger with a computer. It takes about 10 minutes to download the data, change the battery and restart the logger.

Next was to rig the rope in the shaft. I have been trying out a modification to the rig method I used for year. The rope is clipped in to the stanchions above the ladder, as usual. Instead of just letting it drop against the ladder, I use a redirect tied to a stanchion on the opposite side of the silo. This pulls the rope away from the ladder, which saves wear and tear where it crosses the first rung. It also gets the rope in the center of the shaft which makes rappel a bit easier.

Two more small changes are needed. I have been clipping a carabiner around the rope. That works and is safe, but using a pulley would be a bit easier. The second change is to use a lanyard to keep the carabiner or pulley from sliding down the rope. It is in the way when threading the rope through a rappel device.

Seven people were signed up for the trip. Mike and Marty arrived about 8:45, giving us six people. We introduced everyone, then started gearing up. By 9:20 our seventh person had not arrived. We decided to go ahead anyway. The first person went down the shaft at 9:30 and we were all in the cave by 10:00.

Before leaving for the drive, I looked at the National Weather Service radar. It showed some strong storms moving across the silo area between about 3:00 and 4:00 a.m. I was a bit concerned about the water level in the cave, and possibly soggy field for parking. The field was noticibly wet, but was not seriously soggy. All participants had 4×4 vehicles, so we would have had no trouble. Peter and Jessica both reported that a rainstorm had been through the area.

I downloaded the barometric pressure data logger, then went down to the stream to download the first water level logger. The stream level was normal and the water was not silted up. It could still come up, but at that point I figured we could get a full trip.

We all left for the trip down Carroll Passage to the data logger in Carroll River. This was Jessica’s first trip in Carroll Cave, so I pointed out special formations (the boxwork) and other landmarks. We arrived at the Rimstone Room about 10:25. I downloaded the logger and then we returned to the ladder.

We were back at the ladder at 11:00am. We had lunch. The trip to upstream Thunder River went well. The two shower heads were running. Their landing area indicated the river was up about 2 inches from normal. That is almost not noticeable if you are not looking for it. We got into UL2. I downloaded the data logger at about 12:30. There was plenty of time, so we went on to Convention Hall.

Josh White had a VERY bright flashlight with him. He used it to light up the room so Mike and Jessica could take some photos. Everyone climbed up to the overlook except me where they took more photos. We left Convention Hall shortly after 1:00pm.

On the way out I showed Jessica and Peter two very nice formation areas. Mike Kovacs got some good photos. We went straight to Thunder Falls. Peter and Jessica had never seen it before.

The water level above the falls was up only a couple of inches which was enough to produce a rather impressive flow. Everyone walked out to the edge of the falls. We all went down the ladder to get to the bottom of the waterfall. The water level below Thunder Falls was about 6 inches above normal. This shows what we have seen in the data, which is that the cave floods below Thunder Falls first. Real floods above Thunder Falls do not happen until the water level in lower Thunder River rises above the edge of the waterfall.

I downloaded the data logger while the others went up to the waterfall. Peter used Jessica’s phone to get a neat photo of her standing directly in the waterfall. What a way to take a shower!

We were all back at the ladder by 2:30. We geared up and climbed. Last person was out at 3:00. We derigged the shaft, changed clothes and chatted for a bit. Mexican dinner afterwards in Camdenton. Mike, Marty and Jessica took a side trip over to see the natural entrance, so dinner was just me, Josh and Peter.

Radar estimates of rainfall show the Saturday morning storm dropped about 6/10 of an inch. It also rained Friday about 1/2 inch.

We counted 5 fish in Thunder River and 17 more in UL2. We did not see any salamanders. I turned over several rocks to show Jessica isopods. We found several that were around 3 or 4 millimeters long. We did not see any snakes at the base of the ladder.

I took a quick look at the data to see what has happened in the last six months. There were two major floods in April. The first went to about 6 feet in Thunder River. The second went over 14 feet. Downstream from Thunder Falls the level was close to 24 feet. That is a pretty impressive flood! We saw quite a bit of evidence in the stream. There were many new sand banks and most of the footprints were washed away.