David Hobbis

Contact

Email: david.hobbis@vuw.ac.nz
Office: CO505

Qualifications

BSc. Hons. in Geology (pending award) - VUW

BSc in Geology & Physical Geography - VUW

BA in Theatre with an English Literature minor - VUW

MSc thesis

Working Title

Constraining prehistoric rock avalanche occurrence using 10Be and 36Cl cosmogenic surface exposure dating in New Zealand greywacke

Supervisors

Project objectives and description

Project objectives and description: The timescales of mass wasting due to large landslides in New Zealand are poorly constrained because few absolute dates for prehistoric landslides exist. Landslides often accumulate in the path of rivers and glaciers, causing them to be preferentially censored from the geological record. This is problematic not only because landscape evolution fails to account for slope mass movement, but also because the lack of robustly determined large landslide recurrence intervals limits understanding of the hazard they pose; as such, generating a statistically significant dataset of dated landslides is crucial.

A seemingly old rock avalanche deposit five times larger than Wembley stadium (20 million m3) sits at the headwaters of Coal River, which discharges into Lake Tekapo in Canterbury, New Zealand. This previously unstudied rock avalanche (Coal River rock avalanche; CRRA) is primed for expanding the prehistoric large landslide record, and for developing novel methods in geochronology and palaeo-landslide studies.

With the generous support of the Brian Mason Scientific and Technical Trust, we have collected samples from boulders embedded in the deposit surface, which will be processed for 10Be and 36Cl cosmogenic nuclides to determine the age of the CRRA. This will contribute to a growing dataset of dated large palaeo-landslides in New Zealand. Additionally, the novel use of 36Cl nuclides in the Torlesse greywacke lithology of the CRRA – an abundant rock throughout New Zealand, which is often problematic to process for 10Be – expands the applicability of cosmogenic nuclide surface exposure dating across the country.

Rock avalanches also produce microsediment textures known as agglomerates, which are unique to high-stress environments. Sediment samples collected both from within the deposit and from sediments in the downstream riverbed will be imaged using a scanning electron microscope to determine the presence and abundance of agglomerate particles along the avalanche path, and their preservation in downstream deposits. This furthers understanding of the use of agglomerates as a proxy for rock avalanche occurrence in sediment records where preserved deposits are unavailable.

Publications

TBC