Liquefaction structures in Lake Rotoroa (Hamilton Lake)

M.Sc. student Richard Melchert has worked for the Tephra-Seismites group since mid 2021 and assisted with lake coring, sediment description, and other laboratory work. In his recently submitted dissertation entitled “Sedimentology and characterisation of soft-sediment deformation structures within lacustrine successions in 20,400-year-old Lake Rotoroa, Hamilton, New Zealand”, he studied liquefaction structures in Lake Rotoroa, which provide evidence for earthquake activity since the formation of the lake around 20,000 years ago.

Richard used a range of techniques, including X-ray computed tomography (CT), ground penetrating radar (GPR), and grain size analyses. The CT scans enabled him to visualise the liquefaction structures in three dimensions (see figures below).

Vertical flame-like dike penetrating through organic lake sediment (removed during the CT data processing). The dike’s source bed is located within the ~20,000-years-old Hinuera Formation, which underlies the present-day lake sediments.
Five dikes penetrating downwards from a volcanic ash (tephra) layer, having been deposited ~15,600 years ago. The occurrence of these dikes suggest earthquake activity must have happened after the deposition of this tephra layer.
Richard before handing in his dissertation.

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