Developments in mapping and web presentation of fjord-marine deposit distributions for quick-clay related work in Norway

Abstract

For several decades mapping of Quaternary geology has been the basis for quick-clay mapping in Norway. In this context it has been, and still is, of particular importance to define the distribution of fjord-marine deposits that commonly contain clays and silts where layers or pockets of quick clay may have developed. Quick clay may collapse under certain conditions and give rise to disastrous landsliding with severe consequences. It requires careful communication of Quaternary map information to get its full use for quick-clay mapping, landslide hazard assessment and other purposes. For this reason, there has been an increased focus in recent years at the Geological Survey of Norway (NGU) to improve existing web-based map services. This includes for example a National overview of the marine limit (ML) in Norway as the upper natural boundary for the occurrence of marine clays. In addition, a filtered version of Quaternary map information below ML has been added called clay-deposit susceptibility. This map service gives an overview over areas where clay deposits with some probability may be present even under other deposit types. The next step in the development of web services is to include information where the occurrence of fjord-marine clay deposits and quick clay are registered, for example, from drill-hole information. This is now made possible especially with the help of the newly established National Database of Ground investigations (NADAG) hosted by NGU.