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Jamaican Caving Notes |
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Apr 5, 2004 RUDIST ROCK CAVE Position: Flamstead, St James. (GPS position reserved due to paleo). Field notes: R. S. STEWART Cavers: G. van Rentergem, R. S. Stewart, B. Murray, D. Roeber Time in: 12:00 EST, Time out: 13:45 EST THREAT VULNERABILITY: Intermediate Rudist Rock is in the same district as the Cool Garden Caves and is one of the targets for the assessment project. This would be the first of four caves visited this day. We had two new volunteers with us, Brian Murray and Dana Roeber, of the American Peace Corps, out of Manchester. They had made a long trip across by route-taxi to link with us in Falmouth, en route to Flamstead, St James. As usual, we were late, but we nonetheless successfully found them and made the trip to Flamstead via MoBay, arriving before noon. Surprisingly, we found this cave very close to its JU listed position, and no time was wasted in searching for it. In fact, it is hard to imagine how we could have done it more quickly. A road passes within 100 metres of the entrance. With me behind the wheel, and Guy navigating with topo map beside me, we managed to turn down the right lane first try, park, and then quickly find a youth who knew of it. He volunteered to show us the entrance, a two minute walk away. With this soon done, we gathered gear, locked the car, and got at things. Rudist Rock Cave is a stream passage cave that takes water and has cut its way through a rather soft, amorphous, poorly-bedded, limestone. The softness of the limestone has allowed the water to carve a direct route into the hill above that has, to date, managed to extend over 500 metres, until muddy chokes prevent further travel. The particular value of this cave, and it is indeed valuable, is two-fold with both sources quite different: the limestone that this stream-passage has carved its way through is full of fossils; the passage in the outer several hundred metres seldom, if ever, floods completely and thusly supports a very particular collection of inverts. The fossils found in this cave are described more thoroughly in Guy van Rentergem's notes, (accessed via the link above), but I must at least note that they were deposited in the Cretaceous, over 65 million years ago. Since then, Rudist Rock Cave has risen from the sea, sunk into the waters again, and then risen once more. These fossils, that we came across, have a very long and fascinating history. Biologically, this cave has at least one invert species that we have not noted previously, and probably others. This is appears to be the result of several factors that I will list below: The softness of the limestone has allowed the waters to mechanically erode a passage that enables the stream to just keep going. Unlike strongly-bedded systems, where the flow must carve a passage through fractures in hard rock, which in places end, or are blocked by collapse, and thusly results in pooling and backed-up flooded passages during the rainy season, in Rudist Rock Cave this does not happen. It means that there is always an airspace at the top of the stream-passage where resident inverts can avoid being washed away or drowned. In essence, the biological scouring is limited to the lower part of the passage. The catchment for the cave is in fairly level pasture-land and this has caused little siltation compared to the near-by Cool Garden caves. We are seeing a pattern where siltation is dependent on two factors, the degree of cultivation of the catchment and the morphology of the catchment. Stream-passage caves that are fed by catchments that are more "funnel-shaped" will of course send greater flows of water into the cave during the rainy seasons and increase the chance of silt being transported. Highly cultivated land, where there is no forest or grass-cover, allows soil to be transported more easily and this feeds much more silt into the system. A prime example of this siltation process is Cool Garden 1 that has a highly cultivated banana plantation at the upstream end resulting in apx 75% of the vertical profile of the passage having become blocked with mud over the last few decades. Rudist Rock, in contrast, has a gentle slope in the catchment and turf that prevents soil from being easily washed away. This cave deserves a repeat visit to more closely exmaine the biology, and this will be done, but at this time we will note the characteristics of the unidentified invertebrate that was observed. The observation was made by Dana Roeber and follows: "Maroon, segmented, 10-15 segments, with legs on each segment, apx 2 mm long. Underside "tan". Antennae extending apx .3 mm. Observations made with 7x hand-lens. NB, this was not a terrestrial millipede with which we are well-acquainted. There is a bat population, under 100, resident in the outer 50 metres that is supplying a minor amount of guano to the nutrient resource. Sesarma veleryi, (cave crabs), were present in good numbers. There was a subsurface flow into the cave but no surface activity. The flow was minor but present. Note that we were in the cave late in the dry season. A hydrological observation will be made during the June expedition. In closing I must note that both Brian and Dana were of great help. Dana has astounding eyesight and was able to easily spot very small inverts through the course of the entire day that I could barely see. I'm hopeful that we'll have them both along for future sessions. |
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