Post by L Roebuck on Jul 17, 2006 14:16:59 GMT -5
Amboni caves: A fascinating site
2006-07-16 10:05:09
Compiled by Peter Msungu
The Amboni caves are situated at a locality known as Kiomoni past the Kiomoni village about eight kilometres to the north of Tanga, off the Tanga-Mombasa road.
The caves are a geomorphological feature of great scientific interest as well as awe-inspiring and impressive to visit.
The caves have been developed in the Tanga Limestone series, which is of Jurrassic age, and is estimated to extend over an area of 234 kilometres, though the limestone is not exposed in the larger part of this area.
The limestone is only exposed where the Mkulumizi and Sigi rivers and their tributaries have cut deep gorges into the outcrop.
The caves have been a subject of local legends and a number of mythical and awe-inspiring stories have been attributed to the caves.
To the local people the caves are regarded as a supernatural formation and is commonly referred to as Mzimu wa Mabavu, the abode of a powerful deity.
Therefore, apart from the legends and awe-inspiring stories connected with the caves, the local people and people of nearby areas, treat the caves as a place for worshiping where they come to offer prayers, and appropriate the deity in the belief that this all powerful deity will alleviate their sickness, sufferings or increase their fertility.
The remains of these offerings - flag pieces, crucibles with remains of burnt incense, gourds, bottles of oil and perfumes etc can be seen in the entrance chamber.
The caves are, however, an interesting geomorphological phenomena or feature which is common in karstic landforms - landforms developed in limestone areas due to the special nature of the erosion process associated with this type of rock formations.
There are a number of theories which have been used to explain the formation of karstic landforms in limestone areas and all have been used to explain the formation of the Amboni caves.
The classic theory on the formation of such caves is that connected with the nature of erosion of limestone areas - known as the vedose process.
According to this theory, rain water absorbs carbon dioxide in the atmosphere and forms a weak carbonic acid which is capable of dissolving calcium carbonate of which limestone is formed.
When this acidulated rain water percolates through the joints and the beddings and thus forming cavities.
The cavities so formed are enlarged by the same dissolution process along areas of loose jointing or weaknesses and caverns are formed. Subsequently due to the formation of fissures on the limestone surface, surface drainage is captured and streams disappear down pot-holes or swallow-holes and become interlinked through the same dissolution process into extensive systems and their main features are stalagmites, stalact which are downward and upward limestone pillars or columns respectively formed through dripping; dampness with dripping water and stream pools on the surface.
The second theory is that of phreatic origin. According tot his theory, the caves are formed by erosion from the subwater table.
The rain water with carbonic acid percolates through the limestone very rapidly causing very little dissolution and therefore reaches the water table before being a saturated solution of calcium bicarbonate.
At this stage it is still capable of acting as a dissolving agent for the calcium carbonate.
The acidic contents of the water is further strengthened by the carbon dioxide in the ground-water which diffuses downwards.
The acidic contents of the water is further strengthened by the carbon dioxide in the groung-water which diffuses downwards.
The acidulated water in the water table then moves slowly along joints and shale partings between the limestone beds, dissolving the calcium carbonate and thus forming channels. As the channels grow, the flow of the water becomes turbulent and this speeds up the dissolution process.
The channels are consequesntly enlarged into passages and a network of solution passages are formed.
At the junctions of major joint systems, these may be enlarged to become caverns.
This process only stops when the water table is lowered which leaves the caverns dry while the dissolution process begins at a lower level.
This process results in the formation of passages and caverns at different levels which might be joined at some points; a feature found in the Amboni caves.
A third theory which has been advanced to explain the formation of caves in limestone areas is that of sea wave action.
This theory is based on the assumption that at a particular time in the history of the area, the area in question was along a shoreline and therefore subject to wave action.
The waves gradually erodes the limestone block forming caves. It is generally accepted that during the Pleistocene period which concides with the Ice-Age of the northern hemisphere, there were fluctuations in the sea level. These fluctuations were associated with the advance and retreat of the ice.
During the ice-advance a large mass of water was incorporated into the ice sheet, thus causing the sea level to fall, wherease during ice retreat a large mass of water melted, causing the rise in the seal-level.
This has been confirmed by the presence of raised beaches on whose benches are found beach sand and marine fossils. In the case of Amboni area raised beaches have been identified, the highest at 30, 40 metres above the present day sea level and the second at 20 - 30 metres.
It is possible that all the three processes represented by these theories did contribute towards the formation of the Amboni caves. Under this combined process, the first caves would have been formed by the phreatic process disolution from the sub-water level.
When the sea-level rose, the caves so formed would be flooded or the shoreline would have advanced to near the caves area and wave action would have contributed towards the enlargement or modification of the caves.
When the sea-level fell the caves would be left dry, the water table would be lowered and phreatic process would result in the formation of caves at a lower level; these caves at the lower level would equally be subjected to wave action if the sea level rose again.
During the periods of low sea-level and low water table, Vedose process - the dissolution from the surface rain water and percolating acidulated water would be capable of enlarging and modifying the caves.
The caves which are protected and can be visited are those past Kiomoni village on the Northern bank of the Mkulumuzi river known as the Amboni Group.
There are three cave systems in this group, the Amboni, Guano and High Caves.
The entrance to the Amboni caves is through one of the three portals which open into an interconnected group of solution chambers separated by pillars and pinnacles.
SOURCE: Sunday Observer
Full Article: www.ippmedia.com/ipp/observer/2006/07/16/70453.html
2006-07-16 10:05:09
Compiled by Peter Msungu
The Amboni caves are situated at a locality known as Kiomoni past the Kiomoni village about eight kilometres to the north of Tanga, off the Tanga-Mombasa road.
The caves are a geomorphological feature of great scientific interest as well as awe-inspiring and impressive to visit.
The caves have been developed in the Tanga Limestone series, which is of Jurrassic age, and is estimated to extend over an area of 234 kilometres, though the limestone is not exposed in the larger part of this area.
The limestone is only exposed where the Mkulumizi and Sigi rivers and their tributaries have cut deep gorges into the outcrop.
The caves have been a subject of local legends and a number of mythical and awe-inspiring stories have been attributed to the caves.
To the local people the caves are regarded as a supernatural formation and is commonly referred to as Mzimu wa Mabavu, the abode of a powerful deity.
Therefore, apart from the legends and awe-inspiring stories connected with the caves, the local people and people of nearby areas, treat the caves as a place for worshiping where they come to offer prayers, and appropriate the deity in the belief that this all powerful deity will alleviate their sickness, sufferings or increase their fertility.
The remains of these offerings - flag pieces, crucibles with remains of burnt incense, gourds, bottles of oil and perfumes etc can be seen in the entrance chamber.
The caves are, however, an interesting geomorphological phenomena or feature which is common in karstic landforms - landforms developed in limestone areas due to the special nature of the erosion process associated with this type of rock formations.
There are a number of theories which have been used to explain the formation of karstic landforms in limestone areas and all have been used to explain the formation of the Amboni caves.
The classic theory on the formation of such caves is that connected with the nature of erosion of limestone areas - known as the vedose process.
According to this theory, rain water absorbs carbon dioxide in the atmosphere and forms a weak carbonic acid which is capable of dissolving calcium carbonate of which limestone is formed.
When this acidulated rain water percolates through the joints and the beddings and thus forming cavities.
The cavities so formed are enlarged by the same dissolution process along areas of loose jointing or weaknesses and caverns are formed. Subsequently due to the formation of fissures on the limestone surface, surface drainage is captured and streams disappear down pot-holes or swallow-holes and become interlinked through the same dissolution process into extensive systems and their main features are stalagmites, stalact which are downward and upward limestone pillars or columns respectively formed through dripping; dampness with dripping water and stream pools on the surface.
The second theory is that of phreatic origin. According tot his theory, the caves are formed by erosion from the subwater table.
The rain water with carbonic acid percolates through the limestone very rapidly causing very little dissolution and therefore reaches the water table before being a saturated solution of calcium bicarbonate.
At this stage it is still capable of acting as a dissolving agent for the calcium carbonate.
The acidic contents of the water is further strengthened by the carbon dioxide in the ground-water which diffuses downwards.
The acidic contents of the water is further strengthened by the carbon dioxide in the groung-water which diffuses downwards.
The acidulated water in the water table then moves slowly along joints and shale partings between the limestone beds, dissolving the calcium carbonate and thus forming channels. As the channels grow, the flow of the water becomes turbulent and this speeds up the dissolution process.
The channels are consequesntly enlarged into passages and a network of solution passages are formed.
At the junctions of major joint systems, these may be enlarged to become caverns.
This process only stops when the water table is lowered which leaves the caverns dry while the dissolution process begins at a lower level.
This process results in the formation of passages and caverns at different levels which might be joined at some points; a feature found in the Amboni caves.
A third theory which has been advanced to explain the formation of caves in limestone areas is that of sea wave action.
This theory is based on the assumption that at a particular time in the history of the area, the area in question was along a shoreline and therefore subject to wave action.
The waves gradually erodes the limestone block forming caves. It is generally accepted that during the Pleistocene period which concides with the Ice-Age of the northern hemisphere, there were fluctuations in the sea level. These fluctuations were associated with the advance and retreat of the ice.
During the ice-advance a large mass of water was incorporated into the ice sheet, thus causing the sea level to fall, wherease during ice retreat a large mass of water melted, causing the rise in the seal-level.
This has been confirmed by the presence of raised beaches on whose benches are found beach sand and marine fossils. In the case of Amboni area raised beaches have been identified, the highest at 30, 40 metres above the present day sea level and the second at 20 - 30 metres.
It is possible that all the three processes represented by these theories did contribute towards the formation of the Amboni caves. Under this combined process, the first caves would have been formed by the phreatic process disolution from the sub-water level.
When the sea-level rose, the caves so formed would be flooded or the shoreline would have advanced to near the caves area and wave action would have contributed towards the enlargement or modification of the caves.
When the sea-level fell the caves would be left dry, the water table would be lowered and phreatic process would result in the formation of caves at a lower level; these caves at the lower level would equally be subjected to wave action if the sea level rose again.
During the periods of low sea-level and low water table, Vedose process - the dissolution from the surface rain water and percolating acidulated water would be capable of enlarging and modifying the caves.
The caves which are protected and can be visited are those past Kiomoni village on the Northern bank of the Mkulumuzi river known as the Amboni Group.
There are three cave systems in this group, the Amboni, Guano and High Caves.
The entrance to the Amboni caves is through one of the three portals which open into an interconnected group of solution chambers separated by pillars and pinnacles.
SOURCE: Sunday Observer
Full Article: www.ippmedia.com/ipp/observer/2006/07/16/70453.html