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In a technique known as blue field entoptoscopy, the effect is used to estimate the blood flow in the retinal capillaries.The patient is alternatingly shown blue light and a computer generated picture of moving dots; by adjusting the speed and density of these dots, the patient tries to match the computer generated picture to the perceived entoptic dots.
A rift valley is a linear shaped lowland between several highlands or mountain ranges produced by the action of a geologic rift. Rifts are formed as a result of the pulling apart of the lithosphere due to extensional tectonics .
Lake Turkana is an East African Rift feature. [18] A rift is a weak place in the Earth's crust due to the separation of two tectonic plates, often accompanied by a graben, or trough, in which lake water can collect. The rift began when East Africa, impelled by currents in the mantle, [19] began separating from the rest of Africa, moving to the ...
(The ridge also has a secondary rift valley running its length.) The width is an average taken along the spreading ridges (Georgia–Senegal, Brazil – Bight of Benin, etc.). The greatest depth is the Romanche Trench. (The Puerto Rico Trench is not part of the rift system.) Great Rift Valley: 6,000 km (3,700 mi) 220 km (140 mi) 2 km (1 mi)
The Appalachian Mountains had already been nearly eroded flat by the end of the period; the uplift and faulting that was the first part of the rifting provided new sources of sediment for the vast thicknesses deposited in the Newark Supergroup; the igneous intrusions are similarly diagnostic of a rift valley.
The half grabens may have alternating polarities along the rift axis, dividing the rift valley into segments. [ 4 ] Intracontinental and marine rift basins such as the Gulf of Suez , East African Rift , Rio Grande rift system and the North Sea often contain a series of half-graben sub-basins, with the polarity of the dominant fault system ...
West Antarctic Rift System (between red dash lines). Dots are geologic drill holes. Insert map shows approximate extent. Exploration of the geology of the West Antarctic Rift System is limited because apart from peaks of the Transantarctic Mountains that protrude above the ice, much of the region is covered by the Ross Ice Shelf and the vast West Antarctic Ice Sheet.
The Southern Rift Valley lakes are like the Western Rift Valley lakes in that, with one exception, they are freshwater lakes. Lake Rukwa (about 5,670 square kilometres (2,190 sq mi) but quite variable) in Tanzania is the alkaline exception, lying south-east of Tanganyika, and has no outlet.