Rock Lake Bottom Exploration

Dive Site: Rock Lake, New Mexico

Location: Santa Rosa, New Mexico

Type: Sink/Spring Depth ca 300ft/90m

Entry: Shore

Dive Buddy: Scott Hilger

Date: 18 Sep 2010

Time: 9:30 am

Swell: Yes it was

Max Depth: 275ft/84m

Average Depth: 260ft/79m

Visibility: 30ft/10m

Temp: Bottom - 60f/15C

Dil/Bailout Gases: 12/60, 35/25, 50/25 & O2

Bottom time: 20min

Runtime: 110 min

Equipment: GKW- MC 170 mCCR Rebreather,1x40cfO2, 1x80cf50/25, 1x80cf 35/25 / Scott - Twin 130's, 1 80cf Stages 12/60 and 4 deco's/travel 21/35, 35/25, 50/25 and O2

Gas used: GKW - 18cf/510l of Trimix and 10cf/283l O2, Scott - 263cf/7447l of Trimix, 48cf 21/35, 32cf/906l, 52cf/1472l 50/25 and 31cf/877l O2

When Scott and I explored the wall/floor interface at Rock Lake last month, we discussed making a traverse of the bottom of the spring in order to look for additional interesting topology/vents and hints at the detailed structure of the spring. We started discussing the dive a couple of weeks ago, making some preliminary navigational plans and synchronizing gasses.

Since this would be deeper than the MC rebreather with the COPIS can go, I had some modifications to make. I removed the old O2 gas block and replaced it with the MX series gas block, plugging the inlet on the top of the MC electronics head. I also restored the O2 regulator's depth compensation. This would also be the first time I carried three bailout deco gasses and had to decide on how to carry as typically we carry the O2 on a leash with stages for the bulk of the dive on OC. Since I needed the O2 to supply the rebreather I decided to wear it on the inside, the 35/25 on the outside and to leash the 50/25. Under bailout I would use the 35/25, then rotate the 50/25 in during a back-gas break at 80ft.

Because it's pretty hard to make 12/60 in high pressure tanks without a booster, Scott made gas to 3000psi in his HP tanks and his stage, Scott also decided to carry some 21/35 to travel to the end of the descent line and to jump back on it as we did our deep stops in order to soften the impact of shorting us slightly on gas.

When we got together on Friday we quickly agreed we wanted a tune up dive to get used to the gear, check some questionable drysuit repairs and for me to practice with the new O2 injector button which feels significantly different and is no longer flow restricted. We did a nice Tech 2 style dive to 150ft for 30 minutes, exploring a previously visited clay shelf covered in gypsum selenide crystals. I carried the leashed bottle and did a practice rotation during deco and felt comfortable enough to make the bigger dive a go for the next day.

We quickly geared up Saturday morning and I ran through my pre-dive checks. We got in, reviewed the plan one more time and dropped the East descent line. Scott switched off his travel gas at about 170 and after some bottle shuffling we were on our way after 6 minutes. We took a heading of 300deg, toward the NW corner of the spring. The bottom drops steeply from the descent line tie in at 180ft to 260ft. After that it slopes more gently toward the 275ft flats. We swam these flats for a while and Scott switched off his stage after about 12 minutes of use.

During this time we also came across a very old tank with the remnants of a regulator and hard plastic backpack. These had belonged to a diver who died at the spring many years ago and are a sober reminder of the dangers inherent in our pursuit and why we train and dive the way we do. After a bit we encountered some interesting topology including some rather large rocks. We had shallowed at bit by then and were actively looking for vents when we hit our time. I ran RD 3-1 for an average of 260ft, so we had 65 minutes of deco to do. We did 13 minutes in the 120-80ft segment, and 26 minutes in the two shallower segments. As had been my practice previously, at the start of a segment, I boost the PPO2 to 1.4 or so and then let it drift down to 1.0 or so by the end of the segment. During our 26 minutes at 20ft, I played with a lot of juvenile striped bass in the hydrilla and watched a couple of turtles goofing off near the surface. The water past the thermocline was warm and welcoming and looking at the sun after being in darkness for a while was tremendously pleasant. We surfaced slowly after finishing our 20ft deco and greeted the day.

Though we did not locate the rumored 'pit' that defines the absolute bottom it was still a great dive that added to our knowledge of this unique site. The rebreather performed flawlessly again and I look forward to exploring this site further using this tremendous tool.

Tags: Rebreather

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