First steps using GIS

Geology and lithology
of Västerbotten county, Sweden

In these maps of Västerbotten county, we had to practice the use of effective symbology to identify and describe patterns where landslides and gulleys occur based on factors such as the surficial geology, lithology, rivers, and lakes, as well as taking into account the former higher coastline located further inland.

With so many features to represent in a single map, this proved to be a challenge.

Gulleys (symbolized in a questionable pale yellow) are almost exclusively situated below the former higher coastline and found in proximity to softer geological features such as clay, postglacial sand, and gravel, as well as somewhat in line with glaciofluvial sediments. Rivers also play a part in their formation. Based on Västerbotten’s lithology, the land below the former higher coastline is almost exclusively comprised of greywacke, a type of dark gray, firm, and coarse-grained sandstone, and this is the type of lithology that the gulleys are part of.

What explains these patterns is that the land above the red line (northwest) has been above sea level longer than the land below the red line (southeast). This is because, during the past ice ages, the Scandinavian peninsula has been completely covered by vast and thick ice sheets which pressed down on the land, pushing it down. After the ice ages passed and the ice sheets melted, the land started to slowly rise again (i.e. rebound). As the land rose, the coastline moved further out to sea. However, the rising land at the coast was not as dense as the land above the former coastline because it has been submerged in the ocean for a long time. Due to this, water streams and a wide variety of other processes and forces eroded some of the softer rising geology, moving, or in this case sliding, material downward and out, creating gulleys.