HiRes AIRBORNE GEOPHYSICAL SURVEY OF ANGLESEY: A KEY DATASET FOR UNRAVELLING COMPLEX GEOLOGY AND ESTABLISHING AN ENVIRONMENTAL BASELINE

The island of Anglesey (Ynys Môn) lies off the northwest coast of Wales, separated from the mainland by the Menai Strait. Primary geological surveying was published in 1920. Because of the relative antiquity of this data, the island is currently undergoing re-mapping by the British Geological Survey (BGS). The new survey is motivated by a unique and complex set of social and economic drivers, and planning constraints that make the provision of up to date baseline geological data an urgent priority.

Provision of new data is predicted to augment the rich history of scientific research undertaken on the island. The new survey will also underpin geological interpretation and coincides with Anglesey being awarded UNESCO European Geopark status. Together these are expected to contribute to tourism and inward investment to the island which has a relatively weak economy, largely based on agriculture, nuclear power generation and aluminium smelting. These drivers are balanced against demands of understanding and mitigating the environmental legacy of historic coal and copper mining as well the need to support planning decisions motivated by ongoing development of a major international transport node at Holyhead with associated rail and road links.

The new mapping exercise comprises targeted land-survey carried out at 1:10 000 scale, benefitting from a century of geological research on Anglesey as well as remotely sensed data, isotopic analyses, regional soil and stream geochemical datasets and biostratigraphic tools unavailable to the original geologists. It also includes a high resolution airborne geophysical survey (HiRes). The survey employed a unique ‘three-in-one’ capability of magnetic, radiometric and electromagnetic measurements mounted on Twin-Otter aircraft. Some 6,300 line-km of data were acquired at a line-spacing of 200 m. As well as providing valuable insights into the distribution of concealed features and properties of both bedrock and superficial deposits, the new geophysical data along with existing geochemical data will define a baseline against which environmental change can be measured.