Mapping the underground

There aren’t many places on earth that haven’t been explored. Anyone with internet access can take themselves on a journey through remote villages with satellite images. We can navigate with topograpical maps in places we’ve never been. What is left for us to explore?

Well for one, we don’t know what is in the depths of the ocean, but since we don’t have as much money as James Cameron, that is certainly out of reach. Instead, let us have a look another place satellites can’t reach: caves.

Ascending rope in Giant's Staircase cave
Exploring cave system under Mt Owen, NZ. Credit: self

Buchan is a small farming town 350km east of Melbourne, known mostly for it’s karst landscape and cave tours. It is one of few limestone areas in Victoria, with limestone being the main reason of cave formation.

Why are caves important?

Caves are naturally preserving, due to regulated temperatures all year round, limited weathering and minimal human impact. This means, things such as Aboriginal cave art and pleistocene fossils can still be found in the same condition as tens of thousands of years ago. These artifacts have helped us shape our knowledge of history.

Research and exploration of caves has also helped US towns ensure water security. By studying the flow of water underground, scientists can model volumes of water available. Their approach is scientific: inject non-toxic organic dye into flowing water streams and trace their movement. Others have been SCUBA diving such areas and mapping them with more traditional tools.

How are caves mapped?

It is all good and fine to know where water flows in and flows out, but it is never as simple as that! Often caves are formed phreatically (underwater), and may take unexpected turns. When that happens it is important to have an accurate map of flow. It might take a second, but have a think about how caves – places without GPS or even light can be mapped.

Example cave survey
Cave survey. Public Doman (https://en.wikipedia.org/wiki/File:Marble_Arch_Survey_(Brodrick,_H.,_1908).png)

It might suprise you that people have been making accurate maps with nothing more than pencil, paper, magnets and gravity, and a bit of high school maths.

This theory follows from traditional land surveying, where a line is measured from point to point, and measurements of azimuth and grade angle are taken too. As above, this method uses simple trigonometry, specifically plenty of arccos and arctans.

It is a slow moving field, with particular challenges not found in other areas: thick mud, tight spaces and very three-dimensional. Recent improvements include a modified laser distance measure, which is able to record data onto a phone over bluetooth. Computer algorithms also help with solving for errors and for those that are familiar with TeX/LaTeX – draw cave maps!

I can’t wait for the day where we can scan caves like this.


3 Responses to “Mapping the underground”

  1. Jethro Hasoloan says:

    Hi Matthew, I think other way to map underground is by using geophysics. This is because geophysical mapping method can look down in the ground, from few meters to several kilometres and it relies on physical properties in both underground’s soil and bedrock.

  2. mdunwoodie says:

    Compasses are no less reliable as above ground, as long as they are used correctly. There is usually very little interference from the environment around you, but things such as torches can have their own magnetic field which can influence the compass.

  3. Rob Dabal says:

    Great article Matthew. So how about compasses? Are they less reliable underground?