Velocity of basaltic flows indicated by lava‐trees

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Abstract
Many data on the velocity of lava‐flows have been obtained from the Hawaiian Islands, Vesuvius, Etna, and other areas of present‐day volcanic activity. Although velocities ranging from a fraction of a mile to a few miles per hour are usual, reports have been made of velocities as high as 40 miles per hour.To determine the velocities of prehistoric flows, two methods can be used. The first method involves the use of the Jeffreys formula. This formula is for laminar flow and in cgs units is equation image where V is mean velocity with regard to depth, g is acceleration of gravity, A is angle of inclination, d is depth, u is the ordinary coefficient of viscosity, and p is specific gravity. If the depth, gradient, and specific gravity of a prehistoric lava‐flow can be obtained, a reasonable viscosity can be assumed and its approximate velocity calculated.

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