Much of the Lysakerelva's fascination is due to a natural heritage unconquered by the demands of housing and transportation that often signal a dominance of Man over Nature. Geologically the area results from events on a momentous scale; meteorologically it lies 'downstream' from southern England while its flora and fauna are typically north European. The river itself is the outflow of a catchment extending more that a day's walk to the north as Per Christian Asbjørnsen (the collector of Norwegian fairy tales) could relate in 'A summer night in Krogskogen'. A short survey of the many events have the created the geography that we find today will help us to appreciate the importance of Nature's resilience.

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ROCKS AND SOILS

The bedrock of the valley is a coarse mixture of limestone in shale laid down in the Ordovician and Silurian periods from 450 to 400 million years ago. The limestone comes from ancient coral or shells while the shale is mud that has been compressed and warmed. These were laid down when Baltica, the Norway's primeval continent, lay well south of the equator. As it drifted northward through different climate zones the coastal zone rose and fell giving sediments of changing character. These became sedimentary rocks through pressure and folded and faulted in the period of active mountain building in the Permian era (about 250 million years ago). This was caused by Baltica coming into collision with Laurentia, the primeval North American continent.

The valley of Lysakerelva runs north - south and is linked to the Rhine Valley in Germany as part of a large rift across the European continent. The Oslo Graben or Sunkland is a wide strip of extraordinary geological interest extending from Kongsberg to Jevnaker. A series of north-south faults formed as the region subsided and it is along one of these that the river has found and eroded its course. The rift formed as the Baltica and Laurentia began to separate again in a episode that stopped when the opening was about 60 km wide. Much later a new opening became the Atlantic Ocean.

The same Permian period of mountain building produced the intrusions of basalt dikes which penetrated the whole area in a criss-cross pattern from a core which today forms the backbone of Ullernåsen, the ridge to the east that runs 200 meters above sea level parallel to the middle stretch of Lysakerelva. Where these intrusions cross the valley they have resisted erosion producing the many of the falls and rapids.

To the north-west of Bogstad Water lies an approximately circular area some 10 km across which in Permian times sunk about 800 m more deeply than the surrounding bedrock. At the edges of this caldera, magma welled up in a thin zone which can be traced from Voksen Mill past Grini Farm and across Bærum. The whole event caused the surrounding rock to be compressed and heated and therefore somewhat harder and more resistant to erosion. Røa Falls where the river plunges 20 m into softer rock marks the outer edge of this zone.

The successive ice ages starting one million years ago ground down the terrain massively. The enormous weight of the ice sheet also depressed the Scandinavian Peninsula so that the sea shore deposits can now be found 215 m above sea level in the hills above Bogstad Water. It was during this time that the clayey top soil of the valley was deposited. Where the clay has lain undisturbed, shells and seaweed fragments are well preserved. Then around 9500 years ago, the ice front retreated, pausing for a time to deposit the large moraines of sand and gravel. The moraines that cross the golf course and camp ground and dam up Bogstad Water can be traced far to the west and to the east where they also impound the lakes at Sogn and Maridal. Another broad strandline extends around Oslo following the line of Ring Road 3. Around Lysejordet a series of old strand lines are readily identified showing that the sea stood in with a definte depth for extended periods and did not rise uniformly over time.

The soils we find today are limy, either from the clay deposited on the sea floor during the ice ages or from weathering of the limestone/shale bedrock. Along the river where forest has survived, the thin layer of clay which overlies the weathered rock is mixed with humus derived from conifers to produce a reddish, more acidic soil. The thicker clays of the farms to the north are of mixed glacial and marine origin, as are the moraines that dam Bogstad Water. The ice edge and seashore have paused here at different times around 8000 years ago leaving riddles that the geologists still debate.

Today the area is still rising out of the sea at a rate of about 30 cm per century. See THE ICE AGE . In Viking times, there would have been little need for steps and stairs to climb from long ships tied up below Lysaker Falls to the surrounding fields as the watermark was 3 meters higher than today.

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WEATHER AND CLIMATE

Oslo's weather during the summer is similar to other north European cities in having a warm days with occasional rain usually occurring as thunderstorms in the afternoon. The locals define a summer's day as one on which the temperature reaches 20° C. Such days are extremely rare outside the period from mid-May to the end of August. The shortness of the summer is, with the intensity of spring, the distinguishing feature of the climate. Spring is delayed until the final melting of the snow in mid to late April while autumn is heralded by the chilly evenings from early September with the first frost on or about the equinox.

The winter is more severe than more southern parts but less so than the other Nordic capitals, Stockholm and Helsinki ,that lie on the same latitude. The average temperature for Oslo falls below zero around December 1st and climbs back into positive values around March 1st having gone as low as - 5° C in January. During this period Norwegians don't bother to mention the minus sign when they comment on the thermometer reading. Temperatures below -20° C with squeaky snow and astronomical heating bills fortunately don't occur every year. Such conditions occur when gentle northerly breezes become established for many days in a row with a deep low pressure area settling over the Gulf of Bothnia.

A fascinating aspect of Oslo's weather is its close relationship with southern England. The autumn storms come directly from London, usually 18 - 24 hours later. The hurricane force winds that felled so many old trees in Kew Gardens in 1987 dumped 40 mm of rain on Oslo the next evening and blew up Lysakerelva's valley flattening many old conifers especially in the narrowest sections.

The best omen for new snow in winter is a low pressure cell moving up the English Channel on a Wednesday. These pass south of Oslo setting up the easterly winds to bring snow on Thursday in time for the ski trails to be prepared for the week-end!

The real cold, however, comes from the north. Any resident along the valley knows how the air sinking down from Sørkedalen along the floor of the valley is two or three degrees colder than higher up and away from the river. An outdoor thermometer on the river side of our house reads consistently a degree colder than one on the opposite side when the breeze is from the north. The cloud of fog directly above the river when it is open (ice-free) is a sign that the air is well below zero.

After cold winters when the river freezes to a depth of half a meter and the falls create ice palaces, the thaw is a spectacular event when huge blocks of ice crash downstream with a roar loud enough to drown out early morning take-offs from the old Fornebu airport.

Is this climate changing? The physics of the greenhouse effect suggests that 60° latitude should experience the most profound changes. The first frost coming later, the last frost earlier and less intense cold in mid-winter seem to be a pattern these last years. The time scale for judging climatic change is, however, long. As long as Christmas remains white, few of us will complain.

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PLANTS, ANIMALS AND BIRDS

All plants and most animals in Norway are immigrants so the flora and fauna will be familiar to those from northern Europe. With Spring arriving in May; April is an uncertain month in which half the population chases the last patches of snow while others look for coltsfoot ["Hestehov", Tussilago farfara] on sandy, south-facing banks.

In May, the deciduous trees blossom and sprout their first green leaves which luminescence in the evening sunshine. Bundles of sprouting birch twigs are an integral part of decorations for the 17th May. Along the river bank, birch ["Bjerk", Betula], pine ["Furu", Pinus silvestris] and Norwegian spruce ["Gran", Picea albies] are interspersed with maple ["Lønn", Acer platanoides], alder ["Svartor", Alnus glutinosa] and ash ["Ask", Fraxinus excelsior] and an understorey of hazel ["Hassel", Corylus Avellana], pussy willow ["Seljen", Salix caprea] , rowan ["Rogn", Sorbus Aucuparia], elder ["Hyll", Sambucus nigra], juniper ["ener", Juniperus communis] and chokecherry ["Hegg", Prunus padus] whose white blossoms perfume the air in May. The oldest trees in the valley were saplings that survived a hurricane that blew up the valley in 1906, flattening large trees especially in the gorge. The forest floor supports wood anenome ["Hvitveis", Anemone nemorosa] from April and lily-of-the-valley ["Liljekonvall", Convallaria majalis] and wood violets ["Skogfiol", Viola riviniana] from late May to June. In the wetter and darker bottoms, tiny yellow buds of Maigull appear against the green of its leaves in mid-April.

On the former grazing land extending down to the river, the yellow flowers are the first to appear. The calcareous soils support the yellow Star of Bethlehem ["Gullstjerne", Gagea lutea] in early May followed by charlock [Åkesennep, Sinapis arvensis], dandelions ["Løvetann", Taraxacum officinale] and Wild Cabbage ["Åkerkål", Brassica campestris]. In June and early July, flowering grasses and wildflowers can be found in profusion especially on former grazing land.

The animal population is timid. The red squirrel battles to raise its young against the predations of domestic cats but is not yet threatened by the grey squirrel as in the rest of Europe. Badger sets occur but neither animals nor their tracks are common. In winter, elk and the occasional roe deer trek down from the hills to graze in the gardens. Trout can be caught in the upper part of the river and a salmon race has been built at Lysaker.

Bird life is profuse. Great, blue and willow tits, robins, chaffinches, siskin and bull finches, sparrows, blackbirds and nuthatches stay around the houses all winter and among the trees during the summer months, while the cuckoo, woodpecker, wagtail, song thrush and swallow return each spring. Pygmy owl are present throughout the year but rarely seen. One must venture down to the waters edge under the large falls to spot Norway's national bird, the dipper. Larger birds such as pigeons, crows and magpies compete all year round for scraps. In autumn, young Siberian nutcrackers may fly in from the east to feed on hazelnuts and the occasional sparrowhawk will prey on sparrow flocks in the autumn.

Mushrooms and toadstools appear from August as an early sign of autumn. Care is needed to select the edible varieties so consult an expert before filling the pan. There is no need to think twice about wild strawberries or feral raspberries. They can be enjoyed straight away or taken home and preserved or frozen. Or do as the local children: thread strawberries on a blade of grass. For wortleberries or cranberries one needs to head for the hills above Bogstad.

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THE ICE AGES

Everything about the Norwegian landscape is tied to the most recent period of geological time, the Quaternary, when ice sheets, thousands of meters thick over Scandinavia, and spread out to cover northern Europe. Over the past 11/2 million years, the Earth's average temperature has fluctuated, causing a series of ice ages with warmer, interglacial periods when the ice front has retreated. Each advance erased most evidence of earlier advances so that the topography we view today tells us mainly about conditions since the last major advance, which goes under various names according to where geologists studied its greatest extent. Curiously, and for geology students fortunately, all begin with the letter W: Würm in the Alps, Wechsel in northern Germany, and Wisconsin in North America. Along Oslo Fjord it is the most recent retreat, named the Dryas, that has left the clearest mark. The ice retreated over a period of a few hundred years disappearing up beyond Nordmarka 9850 years ago.

The huge volume of water retained as the ice sheets 120 000 years ago lowered the sea level over the whole globe by about 200 m compared with today's mean sea level. About 90 000 000 000 000 000 m³ or 90 petatonnes of ice was supported by the northern parts of the landmasses of America, Asia and Europe which subsided elastically. As the ice melted the sea level rose. At most it covered the Oslo area up to today's 220 m contour. But the geological structure known as the Fenno-Scandinavian Shield had began to spring back.

The retreat was uneven. For long periods the front remained in one location depositing thick layers of moraine, the distinctive mixture of boulder, gravel, sand and clay eroded from the land and released into the sea as the ice melted. Colder periods saw the ice front re-advance southwards pushing the moraine up into even more pronounced ridges. Spectacular examples are the Ra which passes through Rygge and Vestfold. A more modest line of moraines was deposited across the southern edge of Nordmarka 9900 years ago. When soon after, the area rose above sea level, it created Bogstad Water by damming Sørkedalselva and Åborbekken at their confluence. This dam soon overflowed and the water found its way into its old channel washing out the clays that had settled out under water, restoring and widening it to create the Lysakerelva Valley we enjoy today.

While the melting of the ice sheets raised the sea level promptly, the land mass responded as all materials do when a load is released: springing up rapidly at first, decelerating as the restoring forces are expended. By dating organic material in the bottom of undisturbed tarns and lakes, palaeontologists have established that the land was rising 11 cm per year when the highest lakes around the inner basin of Oslo Fjord emerged from the sea, 9750 years ago. Today the rise has slowed to 32 cm per century or 3 mm per year. In Viking times the fjord was about 4 m higher. Vækerø and Sollerudstrand were submerged as were the flats occupied by the old Lysaker Chemical Plant, as far upstream as the Falls.

While any land was below sea level it was continually being covered in silt washed down in great quantities by the meltwater from the glaciers. The finest particles settled most slowly forming pockets of clay when the land rose out of the water. It also enveloped shells and other marine creatures that have been carbon-dated. If the coastline remained in one place for long periods, breaking waves created shelves and eventually washed away the finest silt leaving relatively more sand. This is around the time that the first people came to Oslo Fjord.

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THE RIVER AND ITS WATER

The main catchment of Lysakerelva covers 170 square kilometres. Most of this area lies north of Bogstad Water. The area between the watershed on either side of Lysakerelva itself is only 51/2 square kilometres spread over the 7 km from Osdammen to Lysaker Fjord. The map of the catchment shows the many lakes and rivers which ultimately empty into Bogstad Water and run out into Lysakerelva. With an average precipitation of over 1000 mm falling as rain or snow and modest evaporation, the natural flow would be on average about 4 cubic meter/second flow down the river. In the thaw, and after summer thunderstorms or autumn storms, many times as much can swirl downstream and has in flood raised the waterlevel over the footbridges at Lysejordet and Mehlumøra.

The watershed of the upper catchment is in places hard to identify as many mires and peat bogs drain into surrounding rivers as well as to the Lysaker catchment. Here the terrain is flat and the water seeps only slowly towards the rivers picking up the yellow colour that worries some swimmers at Bogstad. Closer to town, many lakes well known to walkers and skiers, such as Tryvann and Kobberhaugtjern, send a stream down to Sørkedalselva and on to Lysaker.

There have been dams and other "improvements" to the river ever since the 1600's. These were undertaken to provide sufficient water for floating timber down to the saw mills and later to ensure a steady flow to keep the mills operating. In 1913 turbines were installed at Grini and downstream with a total capacity of 540 kW. In the 1930's the City of Oslo began to draw drinking water from Langlivann, and deprived the industrial turbines downstream of their means of power production.

Fishing in the river has been improved by a trout/salmon ladder up Lysaker falls on the lowest reaches of the river.

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HISTORY

Human habitation along Lysakerelva can have begun soon after the ice retreated from the submerged river valley. The extensive old shoreline flats that extend around Oslo Fjord between 60 and 100 meters over today's sea-level mark extended pauses in the rapid rise of the land which had been inundated. These old shorelines can be traced across the Lysaker valley as the former pasture to the south of the Lysejordet ski slope that is crossed by the residential streets of Bjørnerabben and Kvernveien and at "Plassen", the sports fields of Røa Idretts Forening. A small rise beside Kvernveien is capped by a burial mound attributed to the Iron Age while the shoreline itself is dated to 6500 BC. The remains of Early Stone-Age flint working sites have been unearthed on strandlines about 80 meters above today's sea level. These were at sea level about 6000 years ago. By 5000 BC the coastline was at today's 60 m contour and the flats below Lysejordet were at sea level. By the beginning of the northern Bronze Age around 1200 BC, the falls at Granfoss marked the coastline. Finds of artifacts belonging to the Viking Age or Iron Age include a trove of iron bars, and occasional weapons.

Recorded history begins with church property records which show the land to be part of the estate of St Edmunds Monastry on Hovedøya in Oslo Fjord. The Pilgrims Way to Nidaros (Trondheim) crossed the river at Granfoss and continued northward, leaving the catchment at Jar. In the civil unrest of the 12th century, the river at this ford featured in at least one skirmish. With the Reformation, these lands became part of the royal estate until coffers depleted by military adventures led to them coming into private ownership in the 1600 and 1700s. A Swedish advance in the war of 1712 was halted at Lysaker's banks.

The first landowners derived their enormous wealth from the vast timber reserves which they had floated down to saw mills along the river. The built environment from this period is most apparent in the pattern of roads and farmhouses. Only Bogstad Manor and Faabro stand from the boom years of the late 1700s. The one is a carefully preserved monument to a powerful family that dominated Norwegian industry and politics; the other, was until recently a dilapidated curiosity besieged by commerical and motorway development despite it having been home to Christian Tullin one of the few poets in 18th century Norway. It was restored in 2007-8 and has become the headquarters of the property developer of the old Mustad industrial area.

The nineteenth century saw a decline in the timber trade which had maintained the baronial life styles and the rise of Norwegian national identity. Oslo and Akerselva took over as the dominant industrial centre while the port at Lysaker and the factories along the estuary became reserved for the production of polluting and dangerous chemicals and explosives. Around the turn of the century, the hills above the estuary had become home to the elite of the nationalism movement in the arts and politics while Lilleaker remained a working class society right up to the 1950's when Oslo's residential area reached the banks of Lysakerelva. Manufacturing industries continued on the lower river until the major flood in 1987 reduced such activity to wharehousing and Lysaker and Lilleaker began a gradual transformation to modern office blocks served by the west and south coast train line.

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