Morgan Big Spring Cave Survey

Laclede County, MO

February 2002

Ethan Brodsky

(Underwater Photos by Tami Thomsen)


Ethan Brodsky collects data at survey station 12 in Morgan Big Spring.

Background

Several years ago, while running canoe trips down the Osage Fork of the Gasconade River, Micki Feakes brought along her SCUBA gear to look at a small spring she had noticed. To her surprise, the small spring, known locally as Wabiwakema, gave way to a hidden cave system. It was apparent that a diver had been there before, but after asking around, nobody knew who had conducted the initial exploration and no map was available.

On her initial trip to the spring, she noticed some interesting isopods (small white critters) living on the ceiling. She discussed her find with a cave biologist from the Natural History Division of the Missouri Department of Conservation, and he requested that she collect some samples of the lifeforms for further investigation. Her finds are believed to be a unique specimen of Caecidotea and were recorded in the Missouri Biospeleogical Database.

With several new members to our group, we had been looking for a small cave in which to practice survey techniques and develop an effective methodology to apply to our larger ongoing projects. As Micki believed Morgan Big Spring to be about 200-300 feet in length, we thought it would be a good choice, especially considering its shallow depth and biological significance.

Preparation

It was decided that the survey would be conducted over five phases. First was to install a knotted survey line in the cave and set up stations. Second was to take Depth/Azimuth/Distance readings at each station. Third, we made a computer-generated preliminary map to guide our further data collection. Fourth, we measured passage geometry at each station, drawing cross-sections at certain selected points. The fifth (not yet completed) phase, is to create a detailed map for publication.

On the way out of Madison, we made several stops to pick up supplies. Midland Plastics supplied the bulk plastic sheet for our survey slates, and Recreational Equipment Incorporated provided Brunton survey compasses. Just before getting out of town, we realized we had forgotten the jig-saw to cut the slates, so we had to run back to the shop and pick it up.

After a ten hour drive to Falcon, Missouri, we immediately set to work making our slates. Here Tami lays out a grid for data collection, while Ethan works on the laptop outlining procedures for the survey (actually I'm looking at pictures from a recent trip to Florida).


Logistics

Morgan Big Spring abuts private property about half a mile upstream of where Atlanta Road crosses the Osage Fork and is easily reachable by watercraft. After loading our gear from the bridge, we launched our canoe, heavily laden with three sidemount divers and their equipment, and paddled up to the spring. At one point, we had to get out and belay the canoe through a section of rapids.

We used a sandbar near the spring as our staging area to suit up and prepare for the dive. After a final briefing, we swam across the river to start our dive. We did a quick photo shoot in the cavern before we began laying our survey line.

Diving


Micki Feakes enters Morgan Big Spring, followed by Ethan Brodsky.

Missouri spring water has a year-round temperature of 58 degrees, necessitating drysuits, thick gloves and hoods for the hour plus bottom times anticipated in our project. All divers used sidemount configuration, as it was most suited to the cave. Visibility in this particular cave ranged from 5 feet to 20 feet. We began with Tami installing the survey line. We quickly realized that we were in for more than we planned, as Tami counted more than 30 knots (spaced precisely at ten foot intervals) just in the main passage. Additionally, a side passage believed to be a short stub, turned out to run 280 feet from the T intersection. With nearly 600 feet of sidemount passage to document and penetration exceeding 500 feet, this was not as small a cave as we originally believed.

Micki and Ethan followed Tami and set up survey stations along the line, immediately taking Depth/Azimuth/Distance readings at each station. Most of the cave consisted of passages 3-5 feet high and 3-20 feet wide. There was a major restriction about 240 feet in on the main tunnel, where the passage narrows to allow only one diver to work at a time. About 40 feet further on, the main passage ends at the "Cul du Sac." We pushed a very small slit in the corner and extended the line another forty feet, culminating in the "Leave It For Mike" Room, which has three small spring vents and one siphon, all of which are less than one foot high and may only be persued by no-mount exploration.

The side tunnel, which Micki had not fully explored prior to our survey, rose over a breakdown plateau, roller-coastered and dropped through a major restriction into an area of fine sand we called "Micki's Endless Beach." Even a skilled diver cannot avoid completely wiping out the visibility in this room. Bubbles percolate into the ceiling, causing silt to rain down, and suprised fish spastically circle around, banging into diver, floor, and walls alike. Surveying in here was very challenging, requiring a great deal of patience and perserverence. After this section, the cave ends in a room which is a less bit less silty and more spacious and allows the diver to regroup. There are two smaller leads that we left for later no-mount exploration.

Later dives retraced the line to take left/right/up/down data at each station and sketch selected cross-section and plan views. Extra care was taken detailing the cavern section, as it is one of the more picturesque sections of the cave. On a final dive, we removed our survey line from the cave, so there would not be multiple lines.

Cartography

We crunched the data each night on Tami's laptop. This achieved several objectives: it guaranteed that the data would be archived in case a slate was lost on later dives (it could happen to anyone, and I found it anyway, it only took twenty minutes!); it gave us a reality check, making apparent any major errors; and it gave us a preliminary map so that divers had a better working understanding of the cave. We used data from multiple divers on the same section of cave to verify the accuracy of our survey.

Below is one of our preliminary maps, showing what we can produce shortly after getting out of the water. We are in the process of applying all of the cross sectional data and detailed drawings to generate a final map for publication and archival. While it is fairly easy to generate a quick line drawing from raw data, making an asthetically pleasing map that gives an accurate understanding of the cave is both an art and a science. It takes a great of skill and practice to create the maps you see published in cave diving journals.


Data and Basic Plan-View Stick Map


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Ethan Brodsky <brodskye at cae.wisc.edu>