Day 11 Cave Diver Course

Day 11 cave diver course

Written by Robin Cuesta

Owner of Sulawesi Dive Trek. IANTD / TDI Full Cave Instructor. Indonesian Cave Explorer. Triton CCR Instructor.

18 May, 2022

Day 11 Cave Diver Course

Location: Buton Tengah, Muna island.
Cave: Oe Mamba
Dive time:  77 minutes
Cumulated Dive time: 1535 minutes

Deep Diving

Day 11 is a special day. Most of the dive we did during this course were shallow and only a few barely touched 20 meters. This is how most caves are around here. But not all. A few of them reach some more impressive depth. We have a few fracture caves going up to 40/50m, quite a few sinkholes in the 60 meters range, and, the mother of all deep caves: Oe Mamba.
This cave has been one of the first cave explored around by local divers. We eventually explored the deep part with a fellow instructor from Thailand in CCR and touched around 75 meters down where we stopped in front of a bedding plane that seemed to go somewhere. It is so far the deepest underwater cave in Indonesia.

I like to take my students to this cave toward the end of their training so they can experiment an array of very specific characteristics that you find in very few caves around here.

First of all, the depth. 75 meters is a serious depth and even though at this level students are limited to 40m (or deepest certification), knowing that you have still 40 meters under you gives you a very special feeling and sensation.

Secondly this cave is very close from the shore and start from a karstic lake. Basically a 200 meters diameter lake surrounded by cliff, very impressive, beautiful and quiet. The landscape is really unique and there is a very peaceful and nice atmosphere around the location. People living around helps a lot on that matter also. We’re always warmly welcomed and take pleasure exchanging about our passion.

And eventually, the entry of the cave is separated from the surface by a Hydrogen Sulfide cloud. It is a 10 meters thick “cloud” of a reddish color that smells of rotten eggs. It is basically formed by the decaying matter that rot in the bottom of the lake. The expelled gas from this process is trapped between two layers of water with different hydro-chemistry.  This cloud is a very specific phenomenon and the gas is toxic. But this is not a big concern for divers as we’re breathing in our regulator and not directly in the water (yet) and the exposition and concentration are anyway too low to be harmful for divers. We only suggest not to perform mask clearing when crossing this cloud to avoid eyes irritation and also to remove their jewelry, sulfur can stain silver.

This being said, Oe Mamba is a very special cave, and deep cave diving a very special activity.

The first thematic of the day was a very simple phrase to debate: Deep Cave Diving is dangerous and diving deep in cave is one of the big 5 of cave fatalities root causes. Depth should be respected, and treated more seriously than most people do in Open Water. We’ve seen a trivialization of deep diving in scuba diving. Diving past 30 meters is not considered at all anymore as a challenge, and this is wrong; moreover, in caves.

We spent a lot of time talking about “what can go wrong by diving deep”. The effect of narcosis. How to recognize it on yourself? on your buddies? how to “treat” it? Fitness and mental conditioning to limit the risks implied by depth, what will change compared to a shallow dive?
This is an extensive topic, and we frequently referred to dive accidents related to depth and how they could have been avoided. Diving deep on air is never a good idea, especially since Helium have become readily available as is Trimix diving training.  30 meters is a good limit on this matter. Gas density is still tolerable and the effect of narcosis in 30 meters in a cave can be way stronger than 30 meters in crystal clear warm ocean dive. Remember that the narcosis is also related to what’s going on in your mind … and a lot is going on in your mind during cave diving training. I am not saying I never went to more than 30 meters on air in a cave. But this is part of a personal risk-taking profile based on experience and situation. And at this stage of their cave diving life and for a while, 30 meters is a reasonable limit to stick with.

We then reviewed our communication related to depth, no decompression limit and decompression to be on spot when inside the cave and express ourselves clearly. Remember that narcosis does not help you to express yourself clearly, I would say it is the opposite.

And eventually we talked about human and psychological factors related to deep diving. Everything non directly related to diving that could affect your safety and the outcome of the dive. 1-meter dives are usually more forgiving than 30-meters one. That’s a fact.

We finally draw a map of the cave, established a plan and drove the 45minutes from the hotel to the location.

The dive itself was pretty good, usually students enjoy this cave a lot as it is offering very different vibes during the journey. The greenish lake, the redish smelly H2S cloud, the very dark shallow bottom with all the organic black silt, and the white and blue deeper bottom at 75M meters. 4 rooms, 4 ambiances.

As planned the depth brought some new challenges and mistakes has been made. But for every new day, new challenges, new mistakes and new lessons. The general level and awareness is becoming better by the day and the mistakes went from major to minor to very few and little ones.

This training anyway Is not an end per se. It just does not stop after those 10+ days. It is just the beginning of the journey. At the end of the trip the divers will be awarded or not a certification based on their current level of performance. Nothing is guaranteed when it comes to certification level. But anyway, that’s not the point at all.

The point is that students will leave this course being better and safer diver. They will have a clear view on their actual level of risk awareness, and essentials diving skills level. They will know what are their weaknesses and strengths, and will hopefully have the will to get even better and eventually continue their training soon !!

If you missed it you can read Day 9’s report here:

List of all IANTD Courses, visit the IANTD Website :



  1. Day 12 Cave Diver Course - Sulawesi Dive Trek - […] If you missed it you can read Day 11’s report here:: […]

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