Matti Seppälä

Wind Tunnel Studies of Ripple Formation

ABSTRACTA wind tunnel of recirculating type was constructed and used for the study of eolian ripples. The height and wave-length of the ripples were found to be a function of wind velocity. There is a ripple formation period, the length of which depends on wind velocity. During this time fully developed ripples form. After that threshold time ripples are almost stable in size and form except at the high wind velocities which produce “secondary” ripples on the surface of the “primary” ripples and thus cause a decrease in mean wave-length. Material sorting on the rippled surface was studied as well as the migration rate of the ripples. At the beginning of ripple formation a process of sorting of the sand material was found.

Deflation and redeposition of sand dunes in finnish lapland

Abstract Deflation and redeposition of aeolian sands in Finnish Lapland have been studied by analysis of their sedimentology and stratigraphy, by dating buried charcoal layers, and by obtaining TL dates. The thickness of redeposited sands on buried soils ranges from a few decimetres to more than two metres. Original dune formation after deglaciation finished around 7000 BP. Subsequent aeolian activity has been mainly destructive in nature. Deflation started in some regions about 4800 BP, continuing with several breaks until the present. Some deflation basins have stayed active for at least 1300 years. However, it is too early to draw general conclusions for the whole area. Forest fires have been important reactivators of aeolian sand drift, but tend to be rather local events. Change in the ground water table is a basic factor affecting deflation. At present, human impact and overgrazing by reindeer seem to increase deflation.

Rock Jointing and Abrasion forms on Roches Moutonnées, SW Finland

The influence of bedrock structures, especially joints, on the formation of roches moutonnees and different glacial abrasion forms on roches moutonnees were studied in the southwest archipelago of Finland.The size and form of roches moutonnees are closely connected with the frequency and state of joints in the bedrock. The fewer and smaller the joints are, the larger are the roches moutonnees that can be formed. Vertical joints in the direction of the ice movement form the weakest zones and determine the width of the roches moutonnees . Joints dipping against glacial movement determine the dip of the eroded rock surface. Horizontal joints provide a suitable base for large and gently-dipping roches moutonnees , which are normally lower than others with less frequent horizontal joints. Striae, friction cracks, facets, fracture lines, and plucked surfaces, and their positions on the surfaces of roches moutonnees , were observed. On the basis of these observations, a stereographic model of the distribution of different abrasion features on the surfaces of roches moutonnees was produced.

Surface abrasion of palsas by wind action in Finnish Lapland

Palsas at Lake Ahkojavri (69°35′N, 26°11′E), western Utsjoki, Finnish Lapland, display very marked effects of surface erosion. Mainly westerly winds have caused the removal of a layer of peat, in some cases more than 40 cm thick, from the palsa surface. The surface peat of one eroded palsa is radiocarbon dated to 2710±70 years BP. Many palsas with heights of 1.5–3 m are almost bare of vegetation. Cracks typical of vegetated palsa surfaces are either worn away or filled with wind-drifted peat. Erosion takes place in winter by wind-drifted snow and ice crystals abrading the peat surface. Some recently formed palsas have been found on the same palsa mires. They are located among the eroded mature palsas and range from 60 to 80 cm in height and 20 to 30 m2 in area. The new palsas also imply strong wind activity in winter. No unusual development in the depth of the active layer on palsas has been noticed. New permafrost is also found in small peat hummocks called pounus.

Proliferative potential of sporadic and neurofibromatosis 2-associated schwannomas as studied by MIB-1 (Ki-67) and PCNA labeling

Abstract. Neurofibromatosis 2 (NF2), a dominantly inherited disorder, is typically manifested as bilateral vestibular Schwannomas and predisposes to other nervous system tumors. Vestibular Schwannomas also occur sporadically but the onset is usually at an older age. Surgical and histological studies have shown that vestibular Schwannomas of NF2 patients are more invasive than sporadic Schwannomas and that the two groups also have morphological differences. We compared the proliferation activity of 26 vestibular Schwannomas (19 NF2 patients) to that of 27 sporadic cases using the Ki-67 (MIB-1) and PCNA (19A2) monoclonal antibodies. In addition, proliferation was assessed in 20 spinal benign Schwannomas, 4 spinal cellular Schwannomas and 3 spinal malignant peripheral nerve sheath tumors (MPNST). We found a significant difference in the proliferation potential between NF2 and sporadic vestibular Schwannomas (MIB-1-LI: 1.72 ± 0.93 vs 0.95 ± 0.57, p=0.001; and PCNA-LI: 1.40 ± 0.75 vs 0.81 ± 0.52, p=0.001). Age does not explain the detected difference in proliferation, since NF2 vestibular Schwannomas also had higher MIB-1 indices than 34 age-matched sporadic tumors. In spinal tumors, MPNST had higher MIB-1 indices than cellular Schwannomas, and therefore MIB-1 staining may be useful in distinguishing between them. Although the defective NF2 gene is important in the tumorigenesis of both NF2 and sporadic Schwannomas, our results suggest that there are differences in the molecular biology of these tumors.

Characteristics of earth hummocks (pounus) with and without permafrost in Finnish Lapland

Finnish Lapland north of 68°30′N latitude is located in the zone of discontinuous permafrost. Two main types of permafrost have previously been found in northern Finland: palsas in the mires and frost in the bedrock on the barren fell summits. The aim of this study was (1) to investigate permafrost occurrence in the peaty earth hummocks (pounus) in several mires, and (2) model characteristics of pounus with and without permafrost. This study showed that permafrost in Finnish Lapland occurs much more widely and commonly than was previously known. A total of 59% of the studied pounus were found to contain permafrost. Over 90% of the permafrost occurrence in the pounus was correctly classified in logistic regression modelling. The probability of permafrost in a pounu decreased with the height of vegetation, and increased with the pounu height and distance from the running stream. There were clear vegetation differences between pounus with and without permafrost. Unfrozen pounus are characterized by forest and mire species, whereas on the permanently frozen pounus the vegetation is patchier with species indicating drier conditions. Pounus provide an excellent object to study short–term and local variations in permafrost formation due to their small size. They react quickly to variation in temperature, snow depth and precipitation. We conclude that pounus can be classified as sporadic permafrost features in northernmost Europe under modern climatic conditions.

Location, Morphology and Orientation of Inland Dunes in Northern Sweden

By interpreting aerial photographs periglacial inland dunes in the northernmost parts of Sweden were studied. These dunes are now mostly stable. Aspects studied were their position, morphology, ori...

Experimental frost shattering of some Precambrian rocks, Finland

The intensity of frost shattering and the amount and type of debris produced from quartzite, granulite and rapakivi granite samples were studied with laboratory experiments. The experiments were run for 1103 temperature cycles from + 15°C to -8°C. The amounts of debris ranged from 0.01 to 0.8 percentages of debris relative to dry weight of the original samples. Grain size of frost weathered material was mainly in sand and gravel fraction classes. Surface texture of quartz grains was studied with SEM. Shape of the grains was irregular and their edges were sharp. Many of the surfaces were rather smooth. Irregular conchoidal fractures are also characteristic. Very often the surfaces were covered by very small, flat fragments of quartz. Some opened microfissures were also found in the grains. The Finnish rocks seem to be very resistant to frost weathering and postglacial frost shattering has had rather limited importance in landform formation in Finland.

Piping causing thermokarst in permafrost, Ungava Peninsula, Quebec, Canada

Abstract An unusual piping tunnel some 80 cm in diameter and 2.5 m long 2 m below a terrace surface and a second smaller one formed in an ice wedge are reported from the continuous permafrost region in northernmost Quebec (mean annual temperature about −6°C). The hydrology of permafrost and its importance on thermokarst and gully erosion is discussed.

Geomorphological aspects of road construction in a cold environment, Finland

Abstract Traditionally, road alignments followed easy landscapes and suitable landforms. When traffic and the size and weight of vehicles increased and higher speeds were used, straighter roads were required; the easygoing relief could not always be used, and problems arose. Road contractors could save money in building and maintenance costs by considering the geomorphic facts. The examples from Finland document why road construction is very expensive in the conditions generated by severe winters. In Finland, more paved roads cross the Arctic Circle than in the whole of North America. This paper gives examples of geomorphic elements affecting road construction in a cold environment: eskers, drumlins, plains of late and postglacial glaciolacustrine and marine sediments, mires, steep rock cliffs, river channels and ice-dams, fluvial erosion, and palsas. Solutions to these problems include removal of frost sensible materials and replacement by more favorable sediments. Road surfaces, kept snow-free in the wintertime, are subjected to deep freezing. The maintenance of roads can be supported with some solutions that affect snowdrift and icing problems, avoidance of geomorphic factors that cause problems, and by using natural processes to help people. Some examples of how road construction affects geomorphic processes and vice versa are provided. For example, bridges block moving river ice, and on special occasions, road banks cause icing.