To identify and explain the processes which led to the formation of limestone in the areas of Bog Walk, Lluidas Vale, Ty Dixon and Moneague.
On May 20, a group of 4th form Geography students from Meadowbrook High visited the different limestone areas of Lluidas Vale and The Ty Dixon Caves in St.Catherine, and Moneague in St. Ann’s. I collected data by means of photography and jotting down important details. As well as use of the senses, visual being the most effective, as well as tactile perception which was also effective. We went along to the various stops; I took my notes and asked questions thus elaborating on what I didn’t grasp properly.
As the tour guide, Mr. Daley, explained the different features, expounded on their formation as well as provided suggestions for the SBA composition. This information benefits as secondary information. I faced only one challenge which was traversing the landscape in unsuitable footwear and inclement weather. Nevertheless I managed to capture the essence of the areas and their features. I tried to capture the images on the camera as best as I could, by experimenting at different angles, ranges and utilizing close ups to capture the general importance.
Analysis & Discussion
Stop 1: Bog Walk Gorge
Our first stop was along the road within the Bog Walk Gorge, located 5 miles south of the Bog Walk Village one of the oldest historic towns in Jamaica. While at this location, it was evident that the limestone feature formed was composed of pure limestone, because the lighter the rock is in color, is the purer its composition of limestone is. It was also observed that chemical weathering, the change in the chemical structure and sometimes physical appearance of a rock, was acting upon the rock in the form of carbonation. This is the reaction of rainwater, carbon dioxide and limestone to form calcium bicarbonate, a weak carbonic acid which is soluble, making the rock easy to decompose when it comes into contact with water. Clints and Grykes were evident, as visible in figure 1.0, contributing to weathering. Clints and grykes are a result of carbonation in the weaker joints and cracks of a rock leaving ridges and groves. The ridges are Clints and the groves are grykes.
Plate 1.0 (Chemical weathering acting on the rocks)
The entire gorge is rich with lush and varied vegetation which makes for some impressive and dramatic scenery. Another feature formed at the gorge was a cavern, which is a large extensive cave with a deep chamber and interconnecting passages. When the roof of a cave collapses, large depressions called gorges result, hence the name “Bog Walk Gorge”. The gorge was originally an underground river system which collapsed. The cliffs on both sides of the gorge seemed to still possess potential to collapse. The main river has a tributary coming from the Above Rocks District located in St. Andrew. The major river processes in the area are Hydraulic Action, the sheer force of flowing water on the base of the river bed, and Attrition, when rocks, carried by the river, smash together and break into smaller, smoother particles. Stop 2: The Bog Walk Bridge
Our second stop was made at the entrance to the Pleasant Hill Community, The Bog Walk Bridge; 83.9 km away from Kingston. Here we examined a bridge which was oxidizing. This is a chemical reaction in which substances combine with oxygen to form an oxide: For example, the combination of iron with oxygen to form an iron oxide (rust). I saw ridges which descended from the mountains to the lower parts. These are called interlocking spurs. There was also a flood warning system present as well. It showed the heights of the river and the level of seriousness to be taken hence flooding must be a threat to this community. Gabion basins were also observed along the banks to help keep them in place. The width of the river was approximately 10-13m wide (at points).
Plate 2.0 (example of oxidation)
Stop 3: Lluidas Vale, St. Catherine
Our third stop was at Lluidas Vale, worthy Park in St. Catherine. At this location we observed a sinkhole which was its main feature. A sinkhole is when a joint becomes enlarged to such an extent that a deep vertical hole is created, down which a surface may disappear. A sinkhole was created due to a tributary flowing onto the surface and came upon the land rising upward and eroded the foot of the slope. Overtime the tributary then began to flow underground. Not much water was observed on the surface. The land closer to the sinkhole appeared somewhat moist. A Polje was evident at this location; this is an elongated depression or basin, formed by the synchronization of caves. A polje is found in karstic geological regions of the world, with areas usually 5 to 400 km². The polje occurs in Troy Formation. This limestone feature is displaced by NE-SW trending faults to produce large-scale fault blocks, which are important controls on the geomorphology of the area. Geomorphology is the scientific study of landforms and the processes that shape them. A more recent alluvial and limestone debris cover occurs within the vale, whereas the steeply sloping rim of the polje to the west, north and east is within Troy Formation limestone group.
To the south and southwest of the vale, rocks of the Yellow Limestone Group crop out, while further south older cretaceous volcanic and sedimentary strata are exposed. In Luidas Vale processes are dominated by mass is a plateau area that has been severely eroded so that the relief is sharp. The Yellow Limestone Group consists of limestones (Stettin and Chapelton Formations) and clastic rocks (E.g. Guys Hill Formation). The limestone of the Yellow Limestone Group give rise to doline karsts, with low residual hills, with the dolines locally amalgamated to form uvulas in the Stettin Formation movements and surface water erosion, forming a typically dissected terrain, this is the Lluidas Vale polje which is developed within a down faulted block of Tertiary white limestone and it has a strong structural control through NW-SE trending faults. The floor of the vale also appears to be structurally controlled in that a series of down-faulted limestone blocks are present and overlain by a sequence of limestone rubble, bauxitic soils and alluvium which extends to over 30 m thickness.
Lluidas Vale is a Rand- or Border-Polje in that it is not surrounded on all sides by limestone but bordered to the south by volcanic and clastic sedimentary strata of the Central Inliers in the Juan de Bolas Mountains. The latter is the source of the Rio Cobre and Murmuring Brook which flow northwards towards the vale. The Rio Cobre flows north through the centre of the vale, but turns abruptly south eastwards and flows a short distance along the fault scarp before sinking. In the polje, the river and Murmuring Brook are both ephemeral streams flowing only after rainfall. The north and northwest border of the vale is marked by well developed cockpit karst. A number of small alluvial fans occur on this part of the vale in heavy clay soils representing the residue of limestone dissolution.
Much lighter alluvial soils occur on the eastern and southern part of the vale due to more frequent flooding. The western margin of the vale is marked by a less steep slope containing dolines and small conical hills grading to tower karsts towards the polje. There were also caves in the area containing stalactites, stalagmites and pillars. A stalagmite is an icicle like deposit of calcium carbonate which rises from the floor of a cave. A stalactite is another icicle like deposit of calcium carbonate hanging from the caves roof or growing downward. A pillar is a slender vertical structure of stone used as a support or for ornament. These features can be seen a diagram 1.2. The landforms occurred on a west-facing fault scarp above Lluidas Vale polje. The area was also covered with shrubs and natural vegetation mainly closer to the slope.
Stop 4: Ty Dixon
During our stop at Ty Dixon where tower karsts, the name given to all landforms in areas of limestone, and dolines were evident. A doline is a funnel shaped or conical shaped solution hollow which is formed when several shallow holes unite. There seemed to be an eroded highland that left a residual hill forming tower karsts and dolines. The tower karsts seemed approximately 40m tall. A tower karst is isolated steep sided residual hills. At the base at the end of the residual hills, there were shallow caves which were generally covered with shrubs and natural vegetation. The vegetation of the area was cultivated on the flat areas, where irrigation and accessibility is better, of mainly sugar cane while in other areas, like on the tower karsts there were natural vegetation.
Stop 5: Moneague
Moneague was once one of the largest and most important towns in St. Ann, due to its convenient location along the main North to South. The Moneague Ponds was once located on a flood plain. While at this location houses were visible within close proximity of the ponds. Debris such as trees, trunks and barks could be seen in the pond. The soil was heavily saturated with water (waterlogged) and appeared darkened in color. The water in the pond, however was light blue and fairly clear. There was natural vegetation surrounding the pond, this is evident in plates 5.0 and 5.1
Plate 5.0 (Moneague Ponds)
Plate 5.1 (Lush natural vegetation surrounding the ponds)
Effect of Limestone
Limestone affects the environment as it induces highly alkaline dusts which are air pollutants. It also has effects on health, in particular for those with respiratory problems. The dust also has physical effects on the surrounding plants, like it blocks and damages their internal structures and abrasion of leaves and cuticles, as well as chemical effects which may affect long-term survival.
Benefit of Limestone
As it has its effects, limestone also has its benefits. Adding limestone to water in order to neutralize it is known as “liming.” When limestone is added to ponds and lakes, it has the effect of adding calcium and protecting the water from becoming too acidic. The benefit of limestone in this situation is that it restores and helps to maintain the ecology of the water and makes it supportive of aquatic life. It is also an inexpensive method of slowing down acidification. Conclusion
In conclusion to my studies, I have identified the features of limestone in the areas of study. Our first stop was along the Bog Walk Gorge, where the rocks composure was mainly of pure limestone. Chemical weathering was acting upon the rocks resulting in faster decomposition and the formation of clints and grykes. At our second stop, the Bog Walk Bridge, located in the Pleasant Hill community, it was observed that the community bridge was under oxidation. A flood warning system was also visible, suggesting that flooding is a threat to this community. Our stop at Lluidas Vale, Worthy Park in St. Catherine, was the most informative one. Here we observed a sink hole formed by a tributary, As well as a polje in Troy formation. To the South and South West of the vale, rocks of the Yellow Limestone Group crop out, while further south older cretaceous volcanic and sedimentary strata are exposed.
In Lluidas Vale processes are dominated by mass is a plateau area that has been severely eroded so that the relief is sharp. The floor of the vale also appears to be structurally controlled. The North and North West border of the vale is marked by well developed cockpit karsts. Much lighter alluvial soils occur on the eastern and southern parts of the vale due to more frequent flooding. The western margin of the vale is marked by a less steep slope containing dolines and small conical hills grading to tower karsts towards the polje. There were also caves in the area containing stalactites, stalagmites and pillars. During our stop at Ty Dixon where tower karsts and dolines were evident, there seemed to be an eroded highland that left a residual hill forming tower karsts and dolines. We also came across the Moneague Ponds, which was once a flood plain and is now heavily waterlogged. Debris could be seen in the light blue color pond; the soil was heavily waterlogged and appeared darkened in color.
http://www.discoverjamaica.com/gleaner/discover/geography/features.htm Holmes, D. and Warn, S. (2003) Fieldwork Investigations- A Self Study Guide, London: Hodder and Stoughton, 2000.
(1991) The Longman Atlas for Caribbean Examinations, London: Longman Caribbean.
Allen-Vassell, M., Fraser, L. (1993). A Guide to Field Studies in School-based Assessment for CXC Geography.