Helgi Björnsson has worked on several research fields. First, collection of basic data of all main ice caps in Iceland, mapping of their surface and bedrock topography, evaluation of ice volumes and description of subglacial landscapes, and of the location and geometry of subglacial lakes and volcanoes. This work has described a previously unknown part of Iceland, and provided knowledge on glacier erosion, geomorphology and volcanic activity. These data were collected by radio echo sounding. Björnsson has also mapped the interface between cold and temperate ice on Svalbard glaciers with radio echo-soundings.