Santa Rosa Blue Hole Cave

[J-Vo]

One of the most interesting things for me, are the vents at the base of the SW wall between 40' & 50'. Seems like and odd location for water to be coming up through the debris.

John, ever heard of anyone taking a look at the sink west of Rock Lake?

 

[boulderjohn]

One of the most interesting things for me, are the vents at the base of the SW wall between 40' & 50'. Seems like and odd location for water to be coming up through the debris.

John, ever heard of anyone taking a look at the sink west of Rock Lake?

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I didn't even know it was there until now. I don't remember you telling me about vents on the SW wall, either. (I am old; it could be dementia.)

I have dived what is called Post Lake on this screen shot from Google Earth. We have always called it Swan Lake, which is what the filled in sink to the south is called on the map. Post/Swan Lake is only a bit more than 60 feet deep. It is always full, even though it has no inlet or outlet. The ground around it is essentially a swamp.

Farther west than the map showed is Bass Lake. Like Rock Lake, it is on private property, and the owner will not give permission for diving. It is pretty deep, but not as deep as Rock Lake. I don't recall how deep it is.

These lakes were dived with special permission in support of a college study by Mariah. I was not part of that project. IIRC, she concluded a connection between all the sinks. Her brother told me years ago that they put a camera down a very deep well, and it showed nothing but water in all directions.

As I suggested earlier, I believe there may be a potential future sink to the east of Rock Lake, right about where we park our vehicles.

The whole area is full of sinks, most of them dry. You can see a bunch driving west on I-40. I once watched one of those totally bogus "investigative science" shows on the History Channel. It was investigating the claim that after the supposed crash of the alien spaceship near Roswell (100 miles away) in 1947, people hid artifacts in a nearby sinkhole. They spent the entire episode rappelling into sinkholes in the area, never finding anything. At the end, as is typical, they breathlessly announced that through their exhaustive and thorough investigation, they had conclusively proven that there are sinkholes in the area in which artifacts could have been hidden. They did not find any, probably because their thorough investigation did not give them enough time to check them all out.

So, I conclude that there is a massive cave system, possibly bigger than Carlsbad Caverns (about 200 miles away), with many deep collapses, well beneath the layers of sandstone we see at the surface and in which we can hide artifacts from alien landings if the need arises.

 

[apenland01]

I was on the team that tried to open the Blue Hole cave a few years ago. The team (before I was on it) had barely opened it a year before, and we were back to make it a reasonable passage and possibly open it to regular cave diving. The city of Santa Rosa was sponsoring our work in an attempt to gain a tourist attraction.

Yes, I wish that the corps of engineers had not dropped those rocks, but the cave itself stops at the 200 foot level. There is a lot of loose rock, more than 2 dump trucks. In my opinion, we were working our way primarily down a pile of collapsed rubble from the formation of the Blue Hole, created first by a much deeper limestone collapse. I don't think we are missing anything by having it sealed.

This is the curious part to me. I have a hard time reconciling the differences from the 1976 articles and quotes from the recovery divers and the divers well after 1976. Are there public records of the rock dumping event in 1976 or is it anecdotal, just like the recovery divers account? Maybe it was 20 dump trucks worth. Was it 6" river rock or 1/2 ton boulders?

Since the entrance is generally the bottom point, nearly all the gravel/rocks/boulders would have found their way to the bottom. If their goal was to fill it, they may likely have used smaller rocks to force fill the most restricted point at the bottom, which would have been the final restriction point leading to the "big room" described in the diver accounts from 1976....

 

[boulderjohn]

We were told it was 2 dump trucks, but we were told a lot of things that really weren't true. We saw maps of the cave that were not remotely accurate. I really cannot talk with any authority about anything that happened before we went into the cave.

Once inside the room that lies between 110-145 feet deep, if things are nice and clear (rare) and you look up toward the entrance, you can easily see why ill-equipped and ill-trained divers could die there. You see several ways up, and each looks equally enticing. Only one of them goes to the surface, though. Of course, for us, it was the one with the cave line in it.

So let's look at what happened here in a geologic sense. There is a very deep and very thick layer of limestone very far beneath the Blue Hole. It almost certainly has a cave in it, probably a big one, with rooms possibly as large as you can see at Carlsbad Caverns not so far away. Some of those rooms have collapsed. In some cases, that has led to the collapse of the hundreds of feet of sandstone above them, creating sinkholes.This process creates a débris cone of broken rock. In the Blue Hole, the débris cone of broken rock starts at about 65 feet deep and slopes down, spreading out until it very nearly fills the entire sandstone sinkhole, leaving only a small opening at about 85 feet and continuing down to an unknown depth through the true depth of the sinkhole.

Artesian water flowing from the mountains to the west flows through the deep limestone and under the sandstone cap until it finds holes in that sandstone cap, and as a result, the water is forced to the surface. It percolates through the piles of rock, looking for the path of least resistance. There are paths through that broken rock, and the water flows more easily through such paths. In the Blue Hole, one of those paths leads to the little bit of ground that was not filled with the collapsed sandstone. About 45 years ago, the Army Corps of Engineers dumped more broken rock into that area to make it harder for people to go through it.

That open area, small as it is, is vital to the health of the blue hole. If the water just seeps slowly into the bottom of a sinkhole, sediment eventually stops it up, and the water looks for better places to flow up. The water that is there will be murky. With an open channel, the water flows more quickly, and the silt that is working its way up with the water rises up and flows out the outlet, producing a nice, clear body of water.

 

[OTF]

John these are fantastic posts. Absolutely fascinating information and stories to a non-caveperson and non-geologist like myself. Thank you for posting, this is the stuff that makes scubaboard great. Condolences on the loss of your teammate.

 

[rjack321]

So let's look at what happened here in a geologic sense. There is a very deep and very thick layer of limestone very far beneath the Blue Hole. It almost certainly has a cave in it, probably a big one, with rooms possibly as large as you can see at Carlsbad Caverns not so far away. Some of those rooms have collapsed. In some cases, that has led to the collapse of the hundreds of feet of sandstone above them, creating sinkholes.This process creates a débris cone of broken rock. In the Blue Hole, the débris cone of broken rock starts at about 65 feet deep and slopes down, spreading out until it very nearly fills the entire sandstone sinkhole, leaving only a small opening at about 85 feet and continuing down to an unknown depth through the true depth of the sinkhole.

Has no one looked at the geologic maps or better yet well boring logs in this area to make an educated guess at how thick the sandstone might be? Before you get to actual dissolvable rock.

 

[helodriver87]

Has no one looked at the geologic maps or better yet well boring logs in this area to make an educated guess at how thick the sandstone might be? Before you get to actual dissolvable rock.

Deeper than 280' if rock lake is any indication. I found some USGS survey data awhile back of some areas not too far from Santa Rosa that put the limestone band starting at roughly 320'. Obviously, it probably isn't fair to just extrapolate that directly to Santa Rosa, but it seems like a reasonable estimate given that there's no limestone to be found in rock lake.

 

[J-Vo]

https://pubs.usgs.gov/of/2014/1156/pdf/of2014-1156_hi-res-pdfs/of2014-1156_figure_1.pdf