Compaction of Hyaloclastite from the Active Geothermal System at Krafla Volcano, Iceland

Figure 7

Yield curves of hyaloclastites. (a) Yield curves for the surface hyaloclastite, loaded up to (black circles and red triangles) and compacted by loading past to 33 MPa (using the same sample; black squares) and 40 MPa (blue triangles). The samples compacted beyond show elongate yield curves. The transition between brittle and ductile behaviour, termed the critical effective mean stress (critical ), is approximated for each curve and shown by B|D. (b) The same data normalised by dividing each point by its respective value. Peak decreases as the samples are compacted beyond . (c) Yield curves for subsurface hyaloclastites sampled at different depths at Krafla. The yield curves increase in size with decreasing porosity (~increasing depth) as the samples become stronger. The brittle to ductile transition is shown for each curve, except for the sample from 556 m depth, where it was not met within the pressure conditions tested. The dashed lines connecting the measurements are for visual clarity and offer no statistical significance.

(a)

(b)

(c)