Zanzibar, island in the Indian Ocean, lying 22 miles (35 km) off the coast of east-central Africa. In 1964 Zanzibar, together with Pemba Island and some other smaller islands, joined with Tanganyika on the mainland to form the United Republic of Tanzania. Area 600 square miles (1,554 square km).
Geography
Both Zanzibar and Pemba are believed to have once formed part of the African continent, the separation of Pemba having occurred during the Miocene Epoch (about 23 to 5.3 million years ago) while Zanzibar dates from the Pliocene Epoch (about 5.3 to 2.6 million years ago) or even later. Various types of limestone form the base of both islands. Raised sands and sandstones also occur, together with varied residual deposits similar to alluvial strata on the adjacent mainland. Extensive weathering of the limestones combined with erosion and earth movements have resulted in a variety of soils including red earths, loams, clays, and sands. Flat areas of coral limestone occur to the east, south, and north of Zanzibar and on the western islands. In places the coral is overlain by shallow red earth or alluvium.
The general impression of Zanzibar when approached from the mainland is of a long, low island with small ridges along its central north–south axis. Coconut palms and other vegetation cover the land surface. It is 53 miles (85 km) at its greatest length and 24 miles (39 km) broad. The highest point of the central ridge system is Masingini, 390 feet (119 m) above sea level. Higher ground is gently undulating and gives rise to a few small rivers, which flow west to the sea or disappear in the coral country.
The climate is typically insular, tropical, and humid, with an average annual rainfall of 60 to 80 inches (1,500 to 2,000 mm). Rainfall is reliable and well-distributed in comparison with most of eastern Africa. Northeast trade winds blow from December to March and southeast trade winds from May to October. The “long rains” occur between March and May and the “short rains” between October and December.
Limestone
Most limestone is formed by the activities of living organisms near reefs, but the organisms responsible for reef formation have changed over geologic time. For example, stromatolites are mound-shaped structures in ancient limestones, interpreted as colonies of cyanobacteria that accumulated carbonate sediments, but stromatolites are rare in younger limestones.Organisms precipitate limestone both directly as part of their skeletons, and indirectly by removing carbon dioxide from the water by photosynthesis and thereby decreasing the solubility of calcium carbonate.
Limestone is partially soluble, especially in acid, and therefore forms many erosional landforms. These include limestone pavements, pot holes, cenotes, caves and gorges. Such erosion landscapes are known as karsts. Limestone is less resistant to erosion than most igneous rocks, but more resistant than most other sedimentary rocks. It is therefore usually associated with hills and downland, and occurs in regions with other sedimentary rocks, typically clays.
Karst regions overlying limestone bedrock tend to have fewer visible above-ground sources (ponds and streams), as surface water easily drains downward through joints in the limestone. While draining, water and organic acid from the soil slowly (over thousands or millions of years) enlarges these cracks, dissolving the calcium carbonate and carrying it away in solution. Most cave systems are through limestone bedrock. Cooling groundwater or mixing of different groundwaters will also create conditions suitable for cave formation.
The site
Although the cave has been developed for a long time, the President of Tasania visited this place in August 2023 to initiate a important function for all villages in Kizimcazi. A memorial stone at the entrance commemorates this event. The access is free of charge.
Tasks and questions
1. Send me the answers to questions a-d) via e-mail or messenger
2. upload the photo according to requirement e) together with your online log. Please note that logs without answers sent will be deleted.
a) Taking into account the above, describe how the cave was formed.
b) Looking around in the cave, what is the proof for your theory ?
c) What kind of water is at the ground of the cave and what do you think it is used for ?
on site questions and tasks :
d) Standing at the platform before entering the cave, which date is documented in large digits on the left concrete column ?
e) Take a picture with you or a personal item on the platform at the lake of the cave ( see sample )
Have a good and interesting visit !
Sources :
www.britannica.com
wikipedia.org