Detecting desalinisation in quick clays: Geochemical analysis and interpretation of porewater data

Project description
In Norway there have been several large quick clay landslides that have resulted in economic damage and loss of life (NGI, 2020). A better understanding of the processes that make clays prone to quick clay landslides can help prevent landslides in the future. Quick clay landslides occur in marine clays in which the original saline porewater has been replaced by fresh water. The focus of previous research has been on mapping quick clays and studying their mechanical stability and stabilisation. However, the processes responsible for the desalinization of post-glacial marine clays have been somewhat overlooked.

The aim of this project is to use geochemical analysis to identify the processes responsible for the desalinisation of marine clays. The main objective is to study whether the desalinization is driven by homogenous diffusion or localized groundwater flow through clay formations, and whether saline porewater has been replaced by locally sourced groundwater or deeper groundwater from adjacent bedrock aquifers. A second objective is to explore if traces of desalinization can be found in streams that drain the clays.

To achieve these objectives a field trip to the NGI quick clay site is planned to gather porewater samples from marine clays and surface water samples from one or more streams that drain these clays. Geochemical analysis of the samples will be done at UiB Biogeokjemilab & ICP-lab. Analysis will include pH/alkalinity, major and minor element concentrations, and salinity/conductivity. The analysis will include trace ions that may be enriched by weathering and rock-water contact, such as Si, Fe, B, Ba and Sr, ions that are affected by desalinization, such as Na, Ca and Mg that take part in cation exchange on clays, and Br that may be enhanced by membrane effects in marine clays. The results will be compared with seawater and rainfall composition.

Proposed course plan during the master's degree (60 ECTS):
GEOV302 – Data analysis in earth science
GEOV342 – The geochemical toolbox
GEOV229 – Geomorphology
GEOV217 – Geohazards
GEO217 – Hydrology, Ground Water and Geohazards
GEOV205 – Geographical Information Systems: Theory and Practice

Field-, lab- and analysis work: 
Labwork (H2023-V2024) will involve preparing porewater samples, measuring pH, alkalinity, major- and minor element concentrations. This will be done at the Biogeokjemilab and ICP-lab at UiB.

Fieldwork site and date is still to be determined in cooperation with contacts at the NGU and NGI, and is estimated to take roughly 3 days, excluding transport to/from site.