Karst topography is a result of the dissolution of soluble rocks like limestone, dolomite and gypsum. Caves are formed due to weathering of rock deep underground. Cave or cavern is a natural void and is a space large enough so that a human can enter. The study of the formation and development of caves is called as Speleogenesis. Most of the formation of caves takes place in limestone rocks by dissolution.
Ultrasound refers to a sound wave with a frequency greater than the upper limit of human hearing, which is generally over 20 kHz. In general, humans can hear sounds with a frequency between 20 Hz and 20 kHz.
The gravity model has been frequently used for explaining human geographical phenomena in the early years of the twentieth century. According to the gravity model, the migration between two places is directly proportional to the product of the population of the two centres, and inversely proportional to the square of the distance between the two.It implies that the capacity of an area to attract migrants depends upon the size of its population or its economic potential. The distance is considered as a hindrance to the population movement.
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