Palu – Day 2

In contrast to the first day, we focused on geotechnical hazards rather than the structures. Structures were damaged, but principally due to mass movement, with levels of destruction similar to those due to the tsunami in the Palu Bay area.

In the morning we visited Potobo in the south-east of Palu where had significant mass movement had been observed on pre-mission aerial photography. We parked at the landslide toe, walking upwards, initially across the zone of deposition, which had been levelled to remove surface detail except for a few structures. One remaining structure sitting at the bottom of the gully indicated the thickness of material that had been deposited, up to 4-5 m. We continued to traverse up the landslide, noting another uncleared mosque amidst the bull-dozed areas. It was unclear whether the mosques are being left for structural reasons or because of religious sensitivities. The exposure and intense heat then forced us to retreat for an early lunch. It transpired that some areas that had appeared unaffected by the landslide, after checking against the aerial photos had actually moved as a mass over a considerable a distance, up to a kilometer.

After lunch the team visited Balaroa district in the south-west of Palu and observed a similarly destructive landslide. This time we started reconnaissance at the top, observing the failure scarp, which at its highest was 8-9 m. Walking down the landslide it was noted that many of the destroyed buildings had not yet been cleared, painting an even clearer picture of the destructive power of the landslide.

At various locations in the Balaroa area, evidence of significant fault displacement was observed in the form of previously straight roads being offset by up to 4 m.

At the end of the day the team visited the town of Sigi where signs of liquefaction was observed. Contrasting to Petobo and Balaroa, the town of Sigi was largely still in-situ however there was significant ground movement and differential settlement along with tension cracking.  Comparing the aerial photography from Sigi to the other landslide locations suggests there was a different failure mechanism in this area.

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