Orsa, Sweden Orsa, Sweden Orsa is a locality and the seat of Orsa Municipality, Dalarna County, Sweden, with 5,308 inhabitants (2010). It is located in the northern part of lake Siljan, about north of the town Mora. Inlandsbanan and European route E45 run through the town and the railroad Bollnäs-Orsa connects. The southern parts of Orsa are characterized by the Siljan Ring, the ring of lakes and rivers in northern Dalarna formed by the big meteorite strike 365 million years ago. In central Orsa, at the ouflow of river Oreälven a sand bank has been built up, in these days enjoyed by
Siljan Ring by rocks of the Llandovery series (Lower Silurian). During the last ice age the area was covered by a thick icesheet. The bedrock was sculpted by the ice, with the softer Palaeozoic sedimentary rocks being preferentially eroded. These erosional hollows are now occupied by lakes Siljan, Orsa, Skattungen and Ore. In accordance with theories about abiogenic petroleum (that hydrocarbons can be formed without involving material from dead plants and animals), astrophysicist Thomas Gold suggested that there might be major deposits of oil and natural gas in the area. Drilling was carried out in the late 1980s and early 1990s but