Hamilton's seismic risk and lake health being investigated

Team members ready to collect samples. From left: Dr Tehnuka Ilanko (UoW), Dr Marcus Vandergoes (GNS Science), and Chris Morcom, Jordanka Chaneva, and Dr Vicki Moon (all UoW). Photo / David Lowe

Two science researcher squads have teamed up to assess the earthquake risk and lake health in Hamilton and its surroundings.

The Tephra-Seismites team, led by University of Waikato scientists Professor David Lowe and Dr Vicki Moon, researches Hamilton's prehistoric earthquake activities including the surrounding lowlands.

At the same time, the Lakes380 project, led by Dr Susie Wood at the Cawthron Institute and Dr Marcus Vandergoes at GNS Science, is investigating lake history and health.

Both researching teams require sediment samples from lakes in the Hamilton area, says Lowe, "That's why we decided to team up."

Last month the group started by collecting core samples from Hamilton Lake (Rotoroa), Forest Lake (Rotokaeo) and Horseshoe Lake (Waiwhakareke) with sediment up to 20,000 years old.

After analysing the samples, the researchers found the sediments include layers of volcanic ash that were deposited through the air by eruptions in volcanic centres of the central North Island.

Lakes380 team members taking samples at Rotokaeo (Forest Lake) in October. Photo / David Lowe

Five layers even showed possible traces of liquefaction, a phenomenon where sediments turned into fluid, also seen during the Christchurch earthquakes in 2011.

The features of those layers show that some local faults may have been responsible for previously unrecognised earthquakes in the Hamilton lowlands over the past 20,000 years.

"Hamilton is known for having a low to moderate earthquake risk; but our research shows that this might need to be revised," says Lowe.

He adds that by studying the nature of the tephra layers using CT scanning and geotechnical methods, they hope to calculate the intensity of shaking and develop a new understanding of seismic hazard in and around Hamilton.

The Lakes380 team focuses on characterising present-day lake health and analysing the changes over the last 1000 years.

For the research, they use water and sediment samples from around 10 per cent of New Zealand's natural lakes.