Fig. 7

Results of small shear box tests for particles ≤2 mm, horizontal displacement vs shear stress (left column) and horizontal vs vertical displacement (right column). a Synthetic pumice, b Synthetic scoria, c Ascension ash. These tests are limited by the maximum amount of travel available for the sample in the shear box. The rate of change of shear stress vs time has been examined and this shows the rate of change peaking early in the test and then subsiding to alternate between small positive and negative values oscillating around 0. Therefore, we are confident that the peak shear stress value measured is representative