How deep is the silt?

[karstdvr]

This may be a stupid question, but is the silt all organic debris? In the photographs, it looks white, and I always thought it was made up of the limestone of the caves eroding over time.

Silt is a generic term for anything from sand,organic material including mung,to clay. Sand is very forgiving and will settle out of solution very quickly. Florida used to be an ocean bed,so sand is plentiful,in fact one cave system I am surveying everytime I pass a fissure I get rained by a bucketful of sand. Detritus or organic material is typically the black silt we commonly see,this can from decaying vegetation to fecal material. The last type is clay, this is the cave diver's least favorite because it goes into solution quickly and takes a long time to dissipate. Limestone when eroding naturally actually goes into solution and is carried out of the cave. If you see white limestone sprinkling on the cave floor,this isn't silt,but cave diver carelessness by allowing themselves to touch the ceiling. Another item I will put in the silt category is bacteria populations. Bacteria that is not suspended in the water column,but growing in beds on the floor has a silt like behavior. This is easily agitated in the water column and won't go out of solution quickly,not to mention a rare growth may have been permenantly altered (if you see it,please stay away)

 

[Cheekymonkey]

Thank you man that was intersitng, had no idea that it was organic at times.

 

[TSandM]

Thank you -- I learned something!

 

[diveAK]

Im actually studying cave sediments for my masters degree right now. A core pulled out of a cave on the suwannee showed that the top centimeter and a half are younger than a hundred years, and there was an organic deposit (most likely a flood) that we sent off to have radiocarbon dated, and im guessing the organics are younger than 500 years old. And that was only 6 centimeters deep. If you think Ginnie might have alot of sediments, look at pictures of Hole in the Wall, or some of the Leon/river/sullivan sinks systems, now they have some sediments!

 

[karstdvr]

. If you think Ginnie might have alot of sediments, look at pictures of Hole in the Wall, or some of the Leon/river/sullivan sinks systems, now they have some sediments!

You ought to see some of the river caves on the Withlacoochee or Suwannee. There used to be a time that you couldn't swim easily between OG and Challange because of the silt. Interesting contrast between the two,tremendous difference when you don't have much diver traffic.

 

[addexdiver]

You ought to see some of the river caves on the Withlacoochee or Suwannee. There used to be a time that you couldn't swim easily between OG and Challange because of the silt. Interesting contrast between the two,tremendous difference when you don't have much diver traffic.

Thus my point in my previous post that WE as divers have the biggest impact on caves - once suspended the "silts" all go downstream - the longer suspended stuff like the clays go further - an so it becomes suspension time versus flow rate...it makes dives later on easier, but the original cave is no longer there. If you are gonna go in a cave - get your technique as perfected as possible to have the least impact on the cave.

In Potters Delight, it is clay bottom with hard walls - and higher flow. I was told that even the best divers could not originally get through without a total siltout to absolute zero vis - now you can go through and not stir it up much at all...of course you don't see the pristine cave anymore.

 

[karstdvr]

Thus my point in my previous post that WE as divers have the biggest impact on caves - once suspended the "silts" all go downstream - the longer suspended stuff like the clays go further - an so it becomes suspension time versus flow rate...it makes dives later on easier, but the original cave is no longer there. If you are gonna go in a cave - get your technique as perfected as possible to have the least impact on the cave.

In Potters Delight, it is clay bottom with hard walls - and higher flow. I was told that even the best divers could not originally get through without a total siltout to absolute zero vis - now you can go through and not stir it up much at all...of course you don't see the pristine cave anymore.

yep,your right

 

[TSandM]

Well, I dearly hope that, by the time I get to the caves next year, I'll have my buoyancy under precise enough control to be respectful of them. That's why I'm doing all the work I'm doing at home beforehand.

 

[rjack321]

Silt as a geologic/soil science term is a very defined particle size range. By these definitions, silt is larger than clay and smaller than sand. It can be organic but its most commonly thought of as inorganic.

In cave diving terms, silt is anything which may be suspended from seconds (sand) to days (clay). Clays do tend to compact and be somewhat resistant to scour, but once they are stirred up they will stay suspended for a very long time.

Carwash (in MX) really impressed me with the vast quantities of organic matter (mung in cave terms) - both in the basin and sloughing down the sides of the breakdown pile (the heap of rocks in the middle where the ceiling caved in to form the cenote). The mung in the basin was like diving over feathers, just as light and fluffy as can be. While doing our pre-dive drills 3 or 4 ft above it even our (weak) backkicks would stir it up a bit. It looked to me like dead algae. You could put your whole arm into it and never feel bottom (supposedly).

I have no idea how deep the mung is in the actual cave, but in places there are large sticks shoved into it for use as a directional (or secondary depending) tieoff. I tried to wiggle one a couple weeks ago while using it and I would guess there was about 3 to 5 feet of stick below the sediment surface and 2 above (7 ft long overall). It didn't seem to have contacted a hard bottom yet.