Quick Dips

Down Under Queenstown

Geologists from the Institute of Geological and Nuclear Sciences have been looking underneath Queenstown, with the aim of improving understanding of the geology and landscape development of the area.

"Knowledge of the origin of the natural landscape is necessary in order to preserve and manage the landscape in the most appropriate way," says David Barrell, one of the institute scientists working on the Queenstown project.

Glaciers have advanced into the Queenstown/Arrowtown region on several occasions during the ice ages of the last two million years, eroding out the extensive Wakatipu Basin between the ranges in the Lake Wakatipu-Lake Hayes area and leaving behind a variety of deposits. These deposits include poorly consolidated sands and gravels laid down by rivers and streams, fine silty sediments from the beds of ancient lakes, clay and gravel tills deposited by ancient glaciers, as well as debris formed by landslides.

Knowledge of these deposits, and the processes that formed them, is important for site development, groundwater utilisation, identification of construction aggregates and avoidance of natural hazards including landslides, erosion, sedimentation and flooding.

As part of the project, scientists have prepared a 1:50,000 geological map showing the nature and distribution of these deposits.

One thing documented by this study is the presence of extensive landslides on the slopes around the Wakatipu Basin. Another interesting find is a drowned beach 3.5 metres below the surface of Lake Wakatipu, believed to have resulted from a landslide at Kawarau Falls that partially blocked the outlet and caused a small rise in average lake level.

The geological information from this study will be useful for planners and developers in the region and will provide a framework for future geological research.

"Previous studies have focused on the schist bedrock of the region, or on the gold and mineral deposits, but little attention has been paid to the surficial deposits," Barrell says, "Surficial deposits underlie the foundations of most buildings in the region, provide construction aggregates, and contain most of the groundwater resources, so a map that focuses on these deposits is essential for a developing region."