olelog

The highest mountain chains that we see today - like the Himalayas, the Alps, and the Andes - are the result of ongoing and/or recent plate tectonic activity. Later they will be flattened by erosion. Norway's geography is dominated by vast mountain ranges stretching all the way from the south to the north with several peaks above 2000 m - Galdhøpiggen, Norway's highest mountain, is 2469 metres above sea level. These mountains are however in principle a result of the Caledonian mountain building that took place around 400 million years ago, so they should have been eroded away long ago.



And in fact they were. If we look at a period like the Cretaceous (circa 145-65 million years ago), then much of north western Europe was covered by a sea, the so-called Chalk Sea, with extremely clear water and practically no influx of sediments from the surrounding lands, including the Scandinavian Peninsula - this peninsula was flat lowland at that time.



The Scandinavian Peninsula has obviously been uplifted since then. Why, where and when? Well the “wheres” and the “whens” have been largely answered through fission track dating. “Why” is still disputed.

Parts of the Scandinavian mountains have risen by over 1 km over the last 10-20 million years. This permanent uplift varies across Norway, being greatest in south and north, and least in the central region. And we are not just talking about the uplift that took place after the Ice Age, and the removal of the weight of the ice. The uplift took place before the Ice Age.

I remember that there was “some disagreement” about the cause at the Nordic Geological Winter Meeting in Aalborg, Denmark, 2008, (with several papers on the subject) and I hope to hear more on the subject during the next Nordic Geological Winter Meeting to take place in Oslo in January 2010.

During the SCANLIPS project passive seismology was employed to investigate the problem coupled with modelling of potential field data to determine variations in crustal properties and structure across Norway and Sweden.

In the TopoScandiaDeep project scientists will study the composition and properties of the crust and upper mantle below Southern Scandinavia to try to understand why it was uplifted. This will be done using tomographic methods which give an image of the Interior of the Earth by using waves generated by earthquakes or by man-made small surface explosions. They will also use the gravity field, magnetic field and surface heat flow to help constrain the physical properties of the Earth. Finally, the model will be used to test with computer simulations and with tank experiments which forces are necessary to deform the crust and mantle in the way observed today in Scandinavia.

Some geologists believe that the clue must lie in the mantle (that is that the topography is related to processes in the mantle). Therefore they use magnetotelluric methods. Magnetotellurics (MT) is a natural-source, electromagnetic geophysical method of imaging structures below the earth's surface. Natural variations in the earth's magnetic field induce electric currents (or telluric currents) under the Earth's surface. With this method it is possible to see the transition between the upper lithospheric mantle and the somewhat deeper mantle - mapping down to a depth of about 150 km.

I find it nice to know that geologists are still faced with unsolved questions. “Why are the Mountains so High?” is not necessarily as simple a question as it looks.

In Norwegian:
• http://www.ngu.no/no/Aktuelt/2009/Fjellets-gate-gjemt-i-mantelen/