Liquefaction is the process whereby certain types of soil suddenly lose strength, most commonly as a result ground shaking during a large earthquake.

If the shaking is strong enough the pressure of the water against the soil causes the sand and grains to ‘float’ in the water, and the soil becomes liquefied.

Historically, there have either been no earthquakes of sufficient intensity in Taranaki to cause liquefaction, or where earthquakes of sufficient intensity have occurred, there has been no liquefaction. In 2013, a GNS investigation found that, due in part to the region’s geology and low earthquake risk, and the fact that only a few coastal areas have the types of soil that might liquefy, the probability of liquefaction in Taranaki is low and restricted to a few areas.

Those areas identified as having potential to liquefy include Port Taranaki; the lower reaches and tributaries of the Mōhakatino, Rapanui, Tongaporutu, Mimitangiatua (Mimi), Urenui, Onaero and Waitara rivers (in New Plymouth district); and the lower reaches and tributaries of the Waitōtara, Whenuakura and Pātea rivers (in South Taranaki).

Liquefaction at Port Taranaki would damage freight handling areas and thus impact on imports and exports in the region with significant economic effects. However, on average, earthquakes strong enough to cause liquefaction would only be expected every 150 years at Port Taranaki and between 980 and 1,070 years at the river areas.