I did a few dives the other weekend at Perch Lake and Blue Hole. I shot some video in Perch Lake, but unfortunately the lighting conditions weren't the greatest and none of the video really came out. It's kind of a bummer because I was hoping to pull some still frames from the camera of an interesting rock formation in Perch Lake. It looked like a petrified barrel spounge. I'll have to try to find it again and get some pictures of it.
The water conditions at Perch Lake were warmer than this time of the year last year. My gauge registered 51 degrees in Perch Lake, with no noticable thermalcline. Last year about this time the water temperature was around 42 degrees. So far, I've attributing this to the mild fall that we're had this year. I also took some PH test strips with me to test the acidity of Blue Hole and Perch Lake. Perch Lake registered a 7.0 (Neutral) and Blue Hole tested between 6.0 - 6.5 (slightly acidic). I thought that was pretty interesting given we sometime complain about chapped hands, faces, and the chalky residue that is left on our gear after the dives. I always assumed that the water was alkaline. Maybe that's changing?
I also took a some rock samples from Perch Lake and Blue Hole when I was there. I've been gaining some interest in geology recently, so I figured that I would take some rock samples to try to figure out the geology of the region a little better.
First I wanted to get a generalized idea of how old the rocks are in the area. So I found a generalized Geologic Map of New Mexico and determined that most of the area dates back to the Mesozoic era, so 245 mya (million years ago). That includes the Triasic and Jurasic periods. The time period is determined by carbon dating and fossil records. I put a little red circle on the attached map of the region.
The first rock sample that I took was from Perch Lake. The color of the rock is light grey with some hints of a red rust color. Perhaps rust color from an iron mineral oxidizing. It has as a fine grain and some degree of foliation. There is a slight shimmer to the rock when it's held to the light. It's very brittle and can be scratched by rubbing your finger against it. It does not efferves when white vinegar (dilute hydrochloric acid substitute) is applied directly on rock or when the rock is scratched.
I determined that this was a Sedimentary rock called Shale (mudstone).
Perch Lake is interesting, geologically. Many of the rocks that I'vee seen along the wall of the dive seem to be very porus, much like a sponge. The barrel sponge shaped rock is very interesting though. I wonder is the rock is igneous, limestone, or some forgotten reef from a period of time when the area was covered by a shallow sea? The dive interests me more and more every time I slow down to look at the rock formations on the walls. It's very cool and very different from the Blue Hole. I've only seen a single confined area in the Blue Hole that has the same sponge like rock formation.
The remaining rocks are from the Blue Hole. I've been trying to figure out if the Blue Hole was more of a limestone solution type cavern or a cavern formed by volcanic activity for a while. Two samples appear to be limestone, one is dolostone, and the fourth appears to be Sandstone. What else confuses me is the Blue Hole itself. The walls that form the hole are filled with cracks that run in every direction and layers. It doesn't really bare much simularity to the holes that I've seen video of from places like Florida.
Here are the Limestone samples:
Sample number 3 (left upper image), initially confused me. I was starting to think that I had a metamorphic rock because it has large crystals covering about a quarter of the top of the rock. (click the image to see the crystals). I initially thought it was quartz, but soon realized that the crystals were much to soft to be quartz because I could easily scratch them with my finger nail. Once I did the 'fizz' test I realized that the rock was limestone.
Here is the Dolostone sample:
Here is the Sandstone:
Why do I think that the rock is sandstone? The color, hardness (stratches glass), foliation, grain size, and it doesn't efferves with vinegar.
So, out of five rock samples, all five are sedimentary.
The water conditions at Perch Lake were warmer than this time of the year last year. My gauge registered 51 degrees in Perch Lake, with no noticable thermalcline. Last year about this time the water temperature was around 42 degrees. So far, I've attributing this to the mild fall that we're had this year. I also took some PH test strips with me to test the acidity of Blue Hole and Perch Lake. Perch Lake registered a 7.0 (Neutral) and Blue Hole tested between 6.0 - 6.5 (slightly acidic). I thought that was pretty interesting given we sometime complain about chapped hands, faces, and the chalky residue that is left on our gear after the dives. I always assumed that the water was alkaline. Maybe that's changing?
I also took a some rock samples from Perch Lake and Blue Hole when I was there. I've been gaining some interest in geology recently, so I figured that I would take some rock samples to try to figure out the geology of the region a little better.
First I wanted to get a generalized idea of how old the rocks are in the area. So I found a generalized Geologic Map of New Mexico and determined that most of the area dates back to the Mesozoic era, so 245 mya (million years ago). That includes the Triasic and Jurasic periods. The time period is determined by carbon dating and fossil records. I put a little red circle on the attached map of the region.
The first rock sample that I took was from Perch Lake. The color of the rock is light grey with some hints of a red rust color. Perhaps rust color from an iron mineral oxidizing. It has as a fine grain and some degree of foliation. There is a slight shimmer to the rock when it's held to the light. It's very brittle and can be scratched by rubbing your finger against it. It does not efferves when white vinegar (dilute hydrochloric acid substitute) is applied directly on rock or when the rock is scratched.
I determined that this was a Sedimentary rock called Shale (mudstone).
Perch Lake is interesting, geologically. Many of the rocks that I'vee seen along the wall of the dive seem to be very porus, much like a sponge. The barrel sponge shaped rock is very interesting though. I wonder is the rock is igneous, limestone, or some forgotten reef from a period of time when the area was covered by a shallow sea? The dive interests me more and more every time I slow down to look at the rock formations on the walls. It's very cool and very different from the Blue Hole. I've only seen a single confined area in the Blue Hole that has the same sponge like rock formation.
The remaining rocks are from the Blue Hole. I've been trying to figure out if the Blue Hole was more of a limestone solution type cavern or a cavern formed by volcanic activity for a while. Two samples appear to be limestone, one is dolostone, and the fourth appears to be Sandstone. What else confuses me is the Blue Hole itself. The walls that form the hole are filled with cracks that run in every direction and layers. It doesn't really bare much simularity to the holes that I've seen video of from places like Florida.
Here are the Limestone samples:
Sample number 3 (left upper image), initially confused me. I was starting to think that I had a metamorphic rock because it has large crystals covering about a quarter of the top of the rock. (click the image to see the crystals). I initially thought it was quartz, but soon realized that the crystals were much to soft to be quartz because I could easily scratch them with my finger nail. Once I did the 'fizz' test I realized that the rock was limestone.
Here is the Dolostone sample:
Here is the Sandstone:
Why do I think that the rock is sandstone? The color, hardness (stratches glass), foliation, grain size, and it doesn't efferves with vinegar.
So, out of five rock samples, all five are sedimentary.
