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Gurmeet Singh posted an Question
July 30, 2020 • 22:47 pm 30 points
  • IIT JAM
  • Geology (GG)

Sir, why the leeward side of hill get steepened by plucking?

For example, the originally existing small hills or knobs in the river valley, are over-ridden by the glaciers ; and are rounded and smoothened by abrasion on up side, and are steepened by plucking on the down or leeward side, as shown in Fig. Such residual hillocks are called whaleback forms or roches mountonnes.

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    Rahul kumar Best Answer

    Roches mountonnées develop their distinctive morphology due to the pattern of stress on a bedrock surface beneath a sliding glacier. On the stoss side of bedrock bumps, normal stresses are relatively high and particles embedded in the ice are moved across the underlying surface where they carry out abrasion. The evidence of such abrasion is the common occurrence of striations (i.e. scores and scratches on bedrock) on the sloping upper surface and flanks of roches moutonnées. Formation of a roche moutonnée as a result of stress differences over the bedrock surface. High normal stress (pressure) on the stoss face results in bedrock abrasion, whereas lower normal stresses (pressure) on the lee face often allow a cavity to form, which promotes quarrying of bedrock along lines of existing weakness.

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    Sajan sarthak best-answer

    1.FORMATION OF A ROCHE MOUTONNÉE DUE TO PRESSURE DIFFERENCES. HIGH NORMAL STRESS sigma1(PRESSURE) ON THE STOSS FACE CAUSES BEDROCK ABRASION, WHEREAS LOWER NORMAL sigma3 STRESS (PRESSURE) ON THE LEE FACE CAUSES QUARRYING OF BEDROCK ALONG LINES OF EXISTING WEAKNESS.

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    sir why there is pressure difference..and how the pressure (sigma 3) is less on leeward side.

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    Pressure difference because of that rock structure that is like a dome . initially as the glacier flowing from left it will hit the domal at a high pressure at stoss side so it will be the maximum pressure/stress direction i.e sigma 1 and sigma 3 is the minimum stress direction here it's vertical at Lee side..So the domal structure will be more eroded and becomes slender at stoss side and at Lee side the some will be chiped up vertically and becomes steep. imagine a rice bag opened up and hit a rock of domal shape it will hit the back and erode the rock bit Fall by a high force at right of the rock due to gravity. this is exactly that case

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    i got sir

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