Editor’s Note: This article was originally written by Josh “Grubby Wombat” Richards in August 2022 and submitted to Guidelines as a way of promoting cave survey and quietly announcing the discovery of Englebrecht’s East Extension to CDAA members. The discovery was widely announced elsewhere in November 2022 but this article was never published, so it’s being shared for the first time here.

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Like most folks stuck in Melbourne’s lockdown, I didn’t have much to be excited about during 2020. Having finished my cave course in late 2019 and then leaving Mount Gambier under less-than-ideal circumstances, all I could do was dream about getting back to explore the caves I was finally qualified to dive. More than just diving and admiring them though, I desperately wanted to get back to try and understand Mount Gambier’s caves – to get my head around why they’re shaped the way they are, understand how the different rock formations have developed, and (like every new and overly optimistic cave diver) hopefully use all of that to discover something new!

But trapped in lockdown, all I could do was dream, plan… and shop online. A few months into the pandemic I’d learned about a little black box being used by exploration cave divers all around the world to develop quick and relatively accurate line surveys, and I immediately realised the best way to use my COVID-19 relief payment was to send it to an electrical engineer in Mexico called Sébastien. Six weeks later a package from Playa Del Carmen arrived on my doorstep, I opened it up, and started jumping with excitement at the idea of surveying every cave on the Limestone Coast… as soon as the borders reopened.

The MNemo is simply an underwater line-measuring device with a built-in depth gauge and compass. Pulling open a Delrin gate in the middle of the device, you place the cave line inside and lock it into place. From there it’s simply a case of holding the MNemo level to take a compass and depth reading before pushing the MNemo along the line to measure its length. Once you get to the other end, you take a second compass & depth measurement, and the MNemo averages out the two readings and uses the line length to provide a straight-line “shot”. Put a series of these shots together consecutively, and you wind up with a stick map survey of your cave – easy!

When I finally moved back to Mount Gambier and got around to trialling the MNemo, I’d already finished my Advanced Cave course. Given it has a nice combination of cavern areas and some decent tunnels too, Pines seemed like the perfect place to test it out and learn how to use this new-fangled survey tool.

As simple as it is in principle though, the MNemo does take a little bit to truly really understand, and my initial survey of Pines quickly showed how NOT to do things! It turns out not all cave lines are perfectly straight, and when you’re trying to take measurements up a near-vertical chimney into the Crazy Czech Room it’s ridiculously easy to finish one shot and start another without realising you’ve changed depth! Coupled with a misguided attempt to make the survey more accurate by recording lots of small shots (which actually reduces overall accuracy), and a realisation after the dive that the line-measuring wheel hadn’t been fully calibrated; that first survey attempt served more as a learning experience on how to use the device than providing anything useful… but it was a start!

The first survey also showed that I’d need to gain more experience before I tried to survey the deeper parts of Pines properly. What I really needed was a long and relatively shallow cave that could be slowly surveyed without worrying about decompression, and ideally a cave with two or more entrances so I could refine the survey data using separate GPS points. Luckily I knew just the cave for the job: Tank.

As much as I’ve loved helping new Advanced Cave divers gain experience by taking them through their familiarisation “group” dives at Tank, I have to admit to an ulterior motive too – joining your Group 1 & 2 dives provided the perfect opportunity to run the MNemo along lines that more experienced AC divers generally ignore! As I’ve been told plenty of times, the lines in Tank have been resurveyed more times than anyone in the CDAA can remember. However, the experience of using the MNemo there was invaluable – I’ve learned many of the little tricks that improve the quality of it’s data, while getting to explore pretty much every nook and cranny you can without a research permit, AND helping friends get their group dives done too!

With a resurvey of Tank complete and a mountain more cave experience for my efforts, I figured I’d learned enough to tackle Pines again.

Running the MNemo up the chimney into the Crazy Czech Room still isn’t easy or fun, but taking fewer and more accurate shots made all the difference to the overall survey accuracy. Learning more about the MNemo’s mapping software (Ariane’s Line) helped enormously too, and soon the survey of Pines started to reveal all sorts of hidden secrets… or atleast a few things I’d never realised before!

The data from the Wedge Room and the White Room showed they were only meters apart, so on the next dive several of us went back and discovered they were actually connected! The hole may only be big enough to pass a GoPro through, but if you go poking around at the bottom of the Wedge Room (or decide to squeeze through the gnarly stuff at the back of the White Room) you’ll probably find the gap in the rocks where they connect too.

Likewise, surveying into the Director’s Tomb showed that it ended remarkably close to the bottom of the chimney that runs up to the Crazy Czech Room. But inside the Director’s Tomb felt like a dead-end, and there was about 2m difference in the depth of the two lines anyway – no luck! Looking from the other side near the chimney though, we spotted a silty hole in the floor hidden behind some rocks – squeezing down into it, two of us suddenly popped out into a weird and jagged-edged room we quickly recognised as the end of the Director’s Tomb! Might be worth keeping the original name though – “Director’s Tunnel” doesn’t have quite the same ring to it.

Running the MNemo through the most basic and often overlooked caves has proven enormously insightful too, even if it hasn’t led to any discoveries or connections. Even though I’ve dived Allendale East dozens of times, it wasn’t until I looked at the survey data on a satellite map that I realised the cave runs North-West back into the town, rather than South/South-East towards paddocks and the ocean like I thought it did.

What’s really interesting however is the fissure at the very back of Allendale has water coming out of it, and all that water has to go somewhere – there must be a pretty big tunnel buried somewhere under the dirt we all walk down on our way to the water!

Stinging Nettle proved a surprise too – not because it shows a potential connection to Pines, but because it’s going in exactly the opposite direction!

My original mental image of Stinging Nettle was that it had a series of leads all running clockwise around the doline, and surely one of them MUST connect to the Crazy Czech Room in Pines. But the data doesn’t lie, and it turns out all those weird and wonderful leads run North/North-West instead, in precisely the wrong direction to link the two caves.

Likewise, the survey of Englebrecht’s West showed the solution tube under the Habitat’s dry room is disappointingly NOT going to connect to the cave’s main air chamber. Instead of being under the highway in front of the accommodation as we’d hoped, the air chamber is in front of the neighbour two blocks East – far too distant for even the most enthusiastic wombat to connect!

However, the biggest surprise from all this surveying came from one of the “smallest” caves in the Mount. With locked gates, a mountain of stairs, and a hefty climb in or out, most divers see the 20-30m swim between the entrance lake and Englebrecht East’s air chamber as being far more trouble than it’s worth. That attitude might change now that we’ve found more than 400m of new tunnel in it though.

The MNemo can’t take full credit for this discovery – the search for something at the back of Englebrecht’s East started in late 2019 after I read one of Ian Lewis’s 2010 Guidelines articles on cave geology, and has involved a whole lot of really unpleasant wetsuit-destroying dry caving over the last two years I’ve been back in Mount Gambier. The one thing the MNemo has done however has made surveying this Englebrecht’s East Extension (EEX) an absolute breeze. Some sections of EEX are especially nasty – notably the “Caterpillar” (a series of drops from the entrance that lead to the first big room, aka “The Garden”), the “Curiouser & Curiouser” restriction on the Southern branch, and the rockpile between “Tweedledee” and the “Walrus Room”. Squeezing through gnarly new cave in a wetsuit and 7s is challenging enough, so only needing to push a magic black box along the line has made a difficult survey significantly simpler and safer.

After 18 months of quiet but persistent work though, I’ve managed to survey most of Mount Gambier’s known & rated caves with the MNemo. The next challenge will be to see how accurate and effective the MNemo is when faced with the far longer caves on the Nullabor and Roe Plains. But if the data from Mount Gambier is anything to go by, I’m sure we’ll learn all sorts of interesting things and maybe even discover some new tunnels there too!