Surveying and Mapping Caves

How to Survey a Cave and Transform the Data into an Accurate Map

Apr 9, 2009

Cave Surveyor Using a Tape to Measure Distances. , John Pint

A tape, compass and clinometer are used to measure and sketch caves while graph paper and a protractor are employed to produce high-quality cave maps.

True cavers can be distinguished from mere spelunkers by the fact that they regularly produce accurate maps of most of the caves they visit. Through this endeavor, they join the ranks of cave scientists or speleologists and contribute to mankind’s knowledge of what lies beneath the surface of the planet.

Surveying Caves

Cave surveys often start at the entrance to the cave. Some precise spot is designated as Station 0 and measurements are made from here to an exact point inside the cave, which becomes Station 1. A tape is stretched between the two stations and the distance is noted. A compass is used at Station 0 to measure the azimuth or direction to Station 1. Next, the vertical angle between the two stations is measured with a clinometer (also called inclinometer).

Before leaving Station 0, the distances to the left and right walls of the station are measured with the tape as well as the distance from the station to the floor and to the ceiling. The latter will be estimated in many cases. These measurements are shouted by the instrument people to the book person who writes them all down and also draws sketches of each part of the cave.

Typical Cave Survey Equipment

Survey tape. Typically, this is made of fiberglass and is 15 meters (50 feet) long.
Compass. Bruntons and Suuntos are noted for their high accuracy, compact size and resiliency. Be sure not to let a flashlight or headlamp deflect the compass needle during readings.
Clinometer. Again, Bruntons and Suuntos are very popular.
Survey book. These have columns for data on one page and graph paper for sketching on the other. These inexpensive booklets are usually made of waterproof paper.

Making a Cave Map

An accurate map of the cave can be drawn on a piece of graph paper, using data from the cave survey. The top of the page is usually considered north. Decide on the scale and use a 360° protractor to reproduce the compass reading. Then draw lines from one station (represented by a small triangle) to the next.

Correcting Horizontal Distances between Stations

If the cave is not level, the true horizontal distance between stations may be less than what was measured with the tape. Determine the correct distance using a scientific calculator. Find the cosine of the clinometer reading and multiply this number times the distance measured between stations.

Refining the Cave Map

The cave map starts out as a line connecting triangles. The walls of the passages are then drawn using the left and right measurements from the cave survey. Details from the sketch, such as stalactites and large rocks are added. A complete list of symbols for cave maps can be found on one of the websites of the International Union of Speleology. Here and there a cross section can be drawn, showing the shape of the cave passage as seen by a caver inside it. Finally, the cave map should have a title, scale, an arrow showing magnetic (and if possible true) north and the date of the survey, names of surveyors, instruments used, etc.

Surveying and mapping inevitably introduces cavers to aspects of a cavern they might never have noticed otherwise and enhances the overall experience of cave exploration.

The copyright of the article Surveying and Mapping Caves in Caving is owned by John Pint. Permission to republish Surveying and Mapping Caves in print or online must be granted by the author in writing.