Landslides and faulting

Read about the GeoNet response to the Harper Hills landslides after the Darfield earthquake:

Scientists overflew a fault trace 22 km long across late the Last Glaciation (~16,000 years ago) surface of the Canterbury Plains, roughly from west to east. Crosses and offsets to roads, fences, tracks, and irrigation channels were observed. It passed directly beneath two houses and a farm shed, close to at least two other buildings, and under high voltage transmission lines. The trace comprised a series of en-echelon left stepping tears, and numerous cracks and pressure ridges. Patterns varied from field to field. There were numerous places where the offset could be measured – right lateral up to about 3m, with variable vertical throw (mostly <1m). They saw no landform evidence of an earlier fault rupture along this trace.

They observed much flooding at the western end of the trace where the Hororata River had burst its banks. Water was ponding irregularly and flow in channels was greater than other streams nearby. Upstream a groundwater bore seemed to be overflowing.

They then flew to Rakaia Gorge where there were reports of landslides. The Rakaia River was very dirty and brown due to spall from steep cliffs on the sides of the gorge and at Big Ben. The landslides were small (hundreds of cubic metres) but restricted to steep cliffs. They saw small surface scars on the sides of Mount Hutt, but no major landslides or rock avalanches.

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