Calculating Viscosity
Jefferys (1925) derived a formula to calculate the viscosity of a fluid based on its physical properties and flow characteristics. The formula is:
where V is the mean velocity of the flow, g is the coefficient of gravity(9.8 m/sec2), A is the angle of the slope, h is the depth of the flowing liquid, p is the specific gravity of the liquid (2), and n is the coefficient of viscosity.
Macdonald (1954) calculated the viscosity of lava during Mauna Loa eruptions he observed in 1940, 1942, 1949, and 1950. Use Macdonald's estimates and the equation to calculate the viscosity. The units for viscosity used by Macdonald are poises. A poise is 1gm/cm s. Therefore, to make the calculations, all measurements must be converted from meters to centimeters.
Based on your calculations, answer the following questions:
- Which eruptions had the lowest viscosities?
- Why are the viscosities low for these eruptions?
- Which eruptions had the highest viscosities?
- Why is the viscosity high for these eruptions?
- In general, do the estimates show that viscosity increases with distance from the vent?
