As I stated in my previous
post, Tahiti has quite steep terrain which is not typical of a shield volcano. What
is typical, however, is the radial drainage pattern on the island (seen below).
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| Radial drainage basins of Tahiti are apparent by the steep ridgeline radiating out from the center of the main island. (http://www.sciencephoto.com/media/97528/enlarge) |
Tahiti
receives 79 to 315 inches of rainfall annually attributing to constant erosion.
This is evident by the islands deeply dissected gullies through which the
rivers flow. The gullies started out as rills. The rills grew from the constant
flow of precipitation that exceeded infiltration capacity or overland flow. Rainwater
enters the drainage basins and into the rivers radiating from the center of the island.
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| Papenoo river carrying rainwater from the center of volcano. |
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| The lush vegetation shown above displays how Tahiti has some protection from erosion. (http://www.tahitiexperience.com/Infopages/Society/TahitiFile.htm) |
The island
has steep slopes that aid the rivers in the alluvial transport of material. Erosion on some
slopes are hindered by the vegetation from the lush tropical forests.
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| The capital city of Papeete continues to clear vegitation for the growth of the city. (http://www.tahitisouvenirs.com/QsnEN.html) |
Greater
erosion occurs in the towns on the West side of Tahiti-Nui (above) and the croplands of
the Taravao plateau (below). There is less vegetation to prevent erosion because of
agriculture and construction efforts.
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| The plateau of Taravao is subject to erosion from agriculture. Also there are examples of oxisol soils in the bottom left corner of the picture. (http://www.daodao.com/Tourism-g309679-Tahiti_Society_Islands-Vacations.html) |
High temperatures and high precipitation
allow for the process of laterization. This process creates dark red soils
composed of aluminum and iron. Laterization breaks down all other components of
the soil like silica resulting in oxisol soil. The oxisols are very weak in
nutrients for the vegetation (examples above and below). Instead the vegetation must quickly absorb
nutrients through exposed roots, vines and large leaves.
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| Beautiful image of the lush vegitation as well as the oxisol soil of the road. (http://www.weltrekordreise.ch/bilder%20pf/030-P1090560.jpg) |
Tahiti also has
histosols organic soils. Histosols are saturated with water most of the time
and are dark in color. Histosols have more organic matter than oxisols but are not abundant on Tahiti. They can be found near sources of water (see below).
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| The waterfall has histosol soil on either side. Easy to find by the black color. (http://svocelot.com/Landfalls/French_Polynesia/tahiti.htm) |
Tahiti has such a beautiful lanscape because of the thousands of years of erosion from rainfall. This has created an amazing land to explore and observe the beauty of nature.
References:
Ye, F., Sichoix, L., Barriot, P., & Dumas, P. (2010). Modeling the erosion of sheild volcanos: The tahiti case. Retrieved from http://www.interpraevent.at/palm-cms/upload_files/Publikationen/Tagungs
beitraege/2010__690.pdf
Allen, C. (n.d.). Geog 1202: Introduction to physical geography. Retrieved from http://clasfaculty.ucdenver.edu/callen/1202/
