AVSETNING

There has been some discussion concerning classification and definition of
rapid mass movements and related deposits. There seems to be a need for a
clearer systematization and division of the processes and deposits. Vi have
thus developed a classificiation system for rapid mass movements and related
deposits in alpine areas. The system is divided into four groups after the
type process involved: (1) Rockslide/rockfall; (2) Snow avalanche; (3) Debris
flow; and (4) Flash flood. The different processes result in deposits with
characteristic surface features. Knowledge about these features is important
during general mapping projects, because these can point out which slope
processes act in different areas. We have made suggestions as to how symbols
can be used on maps. These data will be of practical use in natural-hazard
mapping projects for land-use planning.

The superficial deposits within the area of map-sheet Asker, southeastern
Norway, are classified and described. The areas above the upper marine limit
(c. 220 m a.s.l) are dominated by exposed bedrock or a thin and discountinuous
cover of till. In the main valleys, below the upper marine limit, fine-grained
sediments dominate. These are commonly overlain by sandy and gravelly marine
shore deposits. Only small glaciofluvial deposits exist, mostly near the heads
of the main valleys. Weathering material overlies most of the Cambro-Silurian
bedrock along the inner part of Oslofjorden. Ice movements and the course of
the deglaciation have been reconstructed. The oldest ice movement was towards
south-east (with Oslofjorden as the confluence area). During the deglaciation
of the mapped area, there was only one main glacial event (the Aker Moraine
event) marking advance or half of the ice-front. The Aker Moraine is dated to
c. 9800 years B.P. Short accounts are given on shorelines, shorelevel displacem
nt and pollen analyses.

The superficial deposits within the area of map-sheet Siljan, southeastern Norway, are classified and described. Most of the hilly areas are dominated by exposed bedrock or a thin and discontinuous cover of till. In the main valleys, beow the marine limit (c. 160-180 m a.s.l.), fine-grained marine sediments and fluvial deposits dominate. Glaciofluvial deposits exist in Siljandalen and Lågendalen as well as in the tributary valley Hærlandsdalen. Ice movements and the course of deglaciation are reconstructed. The oldest ice movements were towards the south, later turning towards SSE and SE. Features associated with gacial events marking small advances or halts of the ice-front during the deglaciation in late Younger Dryas and early Preboreal time have been detected within map-area. The Geiteryggen Ice-marginal deposits are correlated with the Ski Ice-marginal deposits in the Oslofjord region and dated to c. 10 000 years B.P. The mapped area was ice-free 9,850-9,800 years B.P. Short accounts are given on shorelines and shore-level displacement. The potential for different utilization of the superficial deposits is also briefly discussed.

The superficial deposits within the map sheets are discribed and classified according to their genesis. Within map sheet Brattvåg both land and sea areas are mapped. The dominant deposits are tills, marine sediments, weathering material and bogs. The area has been glaciated at least three times during the Weichselian with intervening interstadial periods. The last deglaciation occured some time before 12,300 years B.P., and several moraines were deposited. During Younger Dryas the ice front was situated far to the east of the area, but several cirque moraines were formed within map sheet Brattvåg. The regression was very rapid just after deglaciation and up to 9000 years B.P., but levelled off during Younger Dryas. The Holocene transgression maximum was reached at about 6000-7000 years B.P.

The superficial deposits within the map-sheet are described and genetically classified. Tills are the dominating sediments, but considerable amounts of glaciofluvial and fluvial deposits also occur. Slide and talus deposits occur widely in the valleys and weathering material blockfield is present in the higher areas. The oldest described ice striations probably represent a regional ice movement towards the northwest. This northwesterly ice movement was followed by other ice movements controlled mostly by the regional topograph during the folloving deglaciation. During both periods of glaciation diverging striae provide evidence for the existence of local culmination aeras in the mountains within the map-sheet Sunndalsøra. The progress of the moraine ridges in the Reinsvatnet area indicates the existence of an event, the Reinsvatn event. This event is thought to be of Younger Dryas age. The highest marine level during the deglaciation in Sunndalen occurs at some 145 m a.s.l. Radio carbon dating of shells found in glaciomarine clay indicates that Litledalen was deglaciated 9,740±250 C-years B.P.(T-4516).

The superficial deposits occuring within the mapped area are classified according to their genesis. Finegrained marine sediments are the dominating deposits. The map covers one of the biggest Preboreal glaciofluvial icefront deltas in Norway - the Hauerseter deposit. A silt layer - The Romeriksmjele - covering maine sediments, has been found to be a flood deposit settled during a Preboreal catastrophic flood. Iceflow direction has varied from SE to SV most likely being SV during maximum glaciation and during a late stage of deglaciation. Sealevel was 205 m a.s.l. during the Hauerseter event c. 9,500 BP and 150-160 m a.s.l. approx 9,200 BP. The clay deposits are severely dissected by river- and creek erosion and quick clay slides.

The superficial deposits within the map-sheets are classified genetically and described. The icemarginal line "Bremsnestrinnet" is reconstructed from the positions of terminal moraines in the fjord areas. Radiocarbon dating of the younger event "Tingvolltrinnet" further to the east to some 12 000 years, indicates that the "Bremsnestrinnet" is somewhat older, but no more than 13 500 years, at which time the continental shelf of Norway still thought to be covered by glaciers. Short accounts of the distribution of glacifluvial and fluvial deposits are given. Diverse tests have been carried out and are summarized in the "Grusregister".

The superficial deposits and their morphological features within the area of map-sheet Nordfjordeid, western Norway, are classified and described. Ice movements and the course of the deglaciation are reconstructed. The oldest ice movements had a flow direction towards N and NNW almost independent of the underlying topography. Younger ice movements were directed by the fiords and valleys with flow directions mainly towards W. The deglaciation of the area took place in Allerød and Younger Dryas (11,800-10,000 B.P.), interrupted by two readvances: the Vardehaug moraines (10,700-10,600 B.P.) and the Nor moraines (10,500-10,000 B.P.). Outside the area covered by the inland ice cirque glaciers and glacier caps developed in Y. Dryas, indicating a glacial level limit 650 m lower than today. The Nor level is the most distinct marine level in the area having a dip of 1,4 m/km towards WNW. Tills are subdivided according to thickness and occur mostly where metwater reached the sea at the time of deposition, c. 40-70 m a.s.l. Fluvial deposits are found along rivers and mainly as reworked glaciofluvium in the area between the glaciofluvial deposits and the present sea-level. Marine deposits, mainly found in Eidsdalen and along the sides of the fiords, are deposited in areas which were submerged during the deglaciation. Weathered material is present mainly in areas higher than 1000 m a.s.l. Fluvial deposits are found along rivers and mainly as reworked glaciofluvium in the area between the glaciofluvial deposits and the present sea-level. Marine deposits, mainly found in Eidsdalen and along the sides of the fiords, are deposited in areas which were submerged during the deglaciation. Weathered material is present mainly in areas higher than 1000 m a.s.l., and rapid mass-movement deposits found at the base of the steep hills and valley sides.

The superficial deposits within the map-sheet Kilebygd, southeastern Norway, are classified and described. Most of the area is dominated by exposed bedrock or a thin and discontinuous cover ot till. In the Nordsjø-Vollsfjorden and Skien basins, below the marine limit(c. 145 m a.s.l), fine-grained marine sediments dominate. A large glacifluvial deposit, Geiteryggen, exists at the eastern end of Nordsjø. Ice movements and the course of deglaciation are constructed. The oldest ice movement was towards SSE, later turning towards SE and ESE. Features associated with glacial events marking small advances or halts of the ice-front during the deglaciation in late Younger Dryas and early Preboreal time have been detected within the map-area. The Geiteryggen frontal deposit with the Ski Moraine in the Oslofjord region and dated to c. 10,000 years B.P. The mapped area was ice-free about 9,850-9,900 years B.P. Short accounts are given on shorelines, shorelevel displacement and pollen analysis. The potential for different utilization of the superficial deposits is also briefly discussed.

The superficial deposits within the map-sheet are classified genetically and described. The ice-marginal line "Tingvolltrinnet" is reconstructed from the positions of terminal moraines in the fjord areas. Radiocarbon dating of these moraines shows that the readvance occurred some 12 000 years ago. Short accounts of the distribution of glaciofluvial deposits are given. Diverse technical tests have been carried out on the gravel samples and are summarized in the "Grusregister".