Figure 5: Progressive fracturing in evolving breakout lobe.

(a) Overview of breakout lobe 4 on 4 January, with white box indicating the location of b. Breakout location indicated in Fig. 2a and scale bar, 10 m in length. (b) Close-up of this 4 January image, showing large lava slabs cut by incipient tension fractures metres in length. The crack between 2 and 3 is <0.5 m wide and cuts an otherwise mostly intact slab. Scale bar, 5 m in length. (c) Close-up of the same area as b on 10 January 2012, with the corresponding locations marked by the same numbers as in b. The darker colour is due to rainfall having washed ash from the lava surface. The incipient crack between 2 and 3 has now widened and branched (white arrow), leading to the break-up of an ~5-m-wide portion of the slab to smaller blocks 0.3–2 m across. Through this process, breakouts mature through slab break-up, eventually creating more rubbly material indistinguishable from the rubbly flow facies (Fig. 6). Scale bar, 5 m in length.