Last Ice Age

Nature's archive

If we wish to study cultural history, we consult the national archives and church books. If we wish to study natural history, we must go to the archives where this story is recorded and preserved. In lakes roughly 0.5 mm of sediment are usually deposited each year. The first layer got laid down on lake bottoms when the continental glacier receded. Each year a new sediment layer is laid down, like a carpet over the older one. Today, sediment from lake bottoms gives us a natural archive, sort of like a pile of papers in an office archive, with the oldest records in the lowest layers, and younger and younger ones above these. We can study this archive by taking a core through the sediment layers on the bottom of the lake. Similar records can be obtained from bogs and fjord bottoms. River and glacier archives are more complicated in their construction and therefore more difficult to interpret, but these are also very important.

In Hordaland, as in the rest of Norway, we can simplify geological material into two main types: The one is bedrock, that is, the hard rock surface. This record is from several hundreds of millions to two billion years; from a human perspective, an incredibly long time. The other main type is comprised of the loose deposits that cover this hard ground, for example, all growing soils, moraines, sand, clay, peat, avalanche deposits and sediments on the bottoms of lakes and fjords. The loose deposits are geologically speaking very young and they are nature's archive for the time from the ice ages until today.

The last ice age can be compared to a war, where not only animals and people were chased from their land, but where practically speaking all archives or our previous history were destroyed or flattened to the ground. The loose sediment deposits laid down during interglacials are the first to get eroded away during subsequent glacial periods (ice ages), before the glaciers begin to scour at the hard bedrock. The last glacial maximum therefore represents an almost insurmountable barrier to our knowledge about our natural history earlier in time. But, as in all wars, there are things which miraculously survive, though we cannot explain how or why. In Hordaland, just such a miracle occurred in Fjøsanger.

We have had about 40 ice ages in Norway the past 2.5 million years, interrupted by as many warmer, or in any case milder, interglacials with a climate similar to that of modern day. As one can understand from the above, we must unfortunately concede that we will never be able to find archives that will tell us of Hordaland's history through the vast majority of these ice ages and interglacials. Today, we see only the sum total of all the ice age's work, expressed as deep fjords, valleys and lakes. This is discussed in the chapter about landforms.

Layers from the last interglacial period

At Fjøsanger, on the outskirts of Bergen, a sensational find was made in 1975-77: layers that showed the development of forest, animal life and climate in Hordaland through the entire previous interglacial period, known as the "Eemian". On a global scale this is still a very unusual find for areas that were covered by ice during the last ice age. The Fjøsanger archive survived the last ice age and was the first discovery in Norway that showed how conditions were during the interglacial period, before the onset of the last ice age's 100,000 cold years.

The discovery is described in more detail under the Bergen Municipality (*p. R344) Here it will only be mentioned that the climate in Hordaland was roughly the same as in southern Denmark today. We could perhaps wish for these conditions today, too. But it was - on a geological timescale - a short-lived pleasure. The entire Eemian Interglacial lasted only about 15,000 years, from 130,000 to 115,000 years ago. This is characteristic for the last roughly 1 million years: Each ice age lasted ca. 100 000 years, while the interglacials lasted for 10-30 000 years.

The cold sets in

The Fjøsanger archive is exciting also because the layers which were deposited during the transition from the Eemian interglacial to the last ice age are so well preserved. The first climatic change happened unbelievably quickly, in just the span of a few hundred years. The forest on land and warm-loving animals in the sea disappeared almost instantaneously. The explanation is that the Gulf Stream changed its course. Instead of sending large amounts of warm water northwards along the Norwegian coast, most of the water was directed more toward the south, in toward France and Portugal. But the climate varied also during the ice age. After the glacier first advanced almost to Fjøsanger, a milder period set in and the ice disappeared, practically speaking, from the whole of Scandinavia, before it again got colder and the glacier advanced over Fjøsanger. The moraine deposited by this glacier (called the Bønes moraine) comprises the youngest layer at Fjøsanger.

Hordaland then entered an entirely unknown period. We have no finds from the time between the Bønes moraine, which is ca. 90,000 years old, and the Blomvåg find which is roughly 14,500 years old (discussed below). This means that nearly 80,000 years of Hordaland's natural history is unknown. Nonetheless, there is likely to be layers from this period preserved in Hordaland, and we encourage readers who see layers or fossils under moraines to report these.

In caves in Sunnmøre, layers have been found with thousands of bones from animals and birds dated to 30,000 years old. These are mostly sea birds, seals and fish which today live on Svalbard, but also reindeer and grouse, which suggest that at least a wide belt along the entire west coast was ice free at that time. After this, the valley and fjord glaciers joined together to form a mighty continental glacier that reached all the way out to the outer continental shelf, roughly 25,000 - 20,000 years ago. Here, giant icebergs calved and sailed majestically out to sea. From the ice edge the surface of the glacier rose toward the coast and in over land to the highest knobs of ice overlying Hardangervidda. At this time one could have walked from Vikingbanken nearly to Moscow without seeing anything but ice and snow. In sunshine there would have been a beautiful, glistening snowy surface. But, it was devoid of life. One had to travel all the way to Hamburg in order to find ice-free land, but from there the tundra with its permafrost stretched far into the south of France. Only grass, moss and alpine flowers could tolerate the climate there. The trees and most of the animals that live in Hordaland today would have had to migrate all the way to the Mediterranean in order to survive. We call this period roughly 20,000 years ago the "glacial maximum", because the continental glaciers covering Scandinavia and North America were at their greatest extent then, though this was in fact near to the end of the last ice age.

The start of a new time - our own interglacial

One day the ice began to loosen its grip. Life began gradually to take hold from the bare earth. Our nature: pine forests with deer, grass and sparrows, earthworms and ants, lakes with marshy edges, migrating bird's routes and rest stops and rivers stocked with local salmon; all of these mark the final generation in the development of Hordaland's nature, which began first when the ice melted and the glaciers receded back.

The oldest layer that shows an ice-free Hordaland coast is found at Blomvåg in Øygarden (*see p. R374). The find was made in 1941 and we scientists dream that similar finds will be made today so that the deposits can be studied using modern methods. But the museum samples from Blomvåg have been thoroughly studied and dated using the C-14 method to an age of 12,200 - 12,700 C-14 years, which is comparable to 14,200-14,600 calendar years *(see pane p. ?T69 - står ingenting i boka). Finds from among other things reindeer, a large Greenland whale and different types of shell, show that the climate then was roughly the same as in Finnmark today. We do not know how far the ice edge receded in towards land. There are simply no records to show us this.

However, we do know that it became colder again. The famous bone-bearing layer at Blomvåg is covered by a ground moraine that shows that the ice again advanced over Øygarden and out into the ocean. This was, however, a short cold period, only 200-300 years long, and parts of Sunnhordland's coast remained ice-free.

Even more mild: Allerød-time.

A little less than 14,000 years ago, conditions again became so warm that the glacial tongue melted rapidly back. When the glacier lost its foothold on the islands and islets, it calved rapidly in towards the deep fjords because giant mountains of ice broke off from the front of the glacier. This milder period is named after the city of Allerød in Denmark, where deposits from this period were first discovered roughly a hundred years ago. From the Allerød period, ca. 14,000 - 12,800 years ago, we have found horse mussels, common mussels and periwinkles in Bergen, Os and Eikanger, also as far inland as Ølve and Trengereid. These shells depended on the waters of the Gulf Stream, so in Allerød time conditions in Hordaland must have been like those along the Troms-Finnmark coast today. On land there were thickets of green willow and dwarf birch with lush flower meadows between them. It was still too cold for most types of tree, but the absence of birch forest can perhaps also be attributed to the long migration time from S. Europe (*p. ingen sidetall oppgitt i boka, s. 71).

But the ice age was not over: Yngre Dryas-time

During Allerød time the ice front receded, as mentioned, far into the fjords and valleys. Animals and plants from the whole of Europe were en route northwards to exploit the new land becoming exposed and adapt to the steadily warming climate. But they had got it wrong. The climate reversed, abruptly and dramatically. This climatic catastrophe was caused by the Gulf Stream again turning south toward Portugal, instead of flowing north to us.

The ice in Hordaland grew thicker and advanced, mowing down vegetation on land and ploughing up clay and shell from the sea floor. But it didn't take everything with it. Perhaps there was too little time. The shells from the Allerød were of course disturbed by the ice, crushed and stirred up with clay and gravel. But sufficiently large bits survived to make it possible to find them today, identify the species, and date them using the C-14 method. This allows us to decide how far inland ice-free conditions reached during the Allerød, before the last glacial advance.

The Younger Dryas is the name of the roughly 1,000 year-long cold period we are talking about (12,800 - 11,500 years ago). The name comes from the beautiful alpine flower mountain avens, which in Latin is called Dryas octopetala . Leaves from this were found in clay in Denmark already at the end of the 1800s, and this helped researchers then to understand that there had been a cold period.

But back to the ice sheet in Hordaland, which advanced from the inner fjords with incredible speed, roughly 50 m per year. The ice sheet was up to 1500 m thick along the fjords. On land, and especially in the mountains, the thickness was less, but it acted nonetheless like a bulldozer as it moved over Hordaland.

The ice stopped at Herdla. The loose deposits that form this beautiful island were laid down by the ice front when it stopped advancing at the end of the Younger Dryas (*p. R350). Geologists use the name Herdla moraine for the entire end moraine that was formed in Hordaland at that time. This corresponds to the Ra moraine through Østfold and Vestfold municipalities. We draw the Herdla moraine on a geological map with a red line. In nature it appears as a green belt from north to south through Hordaland, because there is deeper soil here and therefore better growing land. Ironically, several of the best farms in the municipality can thank a 12,800 year old climatic deterioration for their good soil. The series of farms, LeirvågAustrheim-Manger-Husebø-Herdla, lie on this moraine, either on moraine soil or on clay and sand deposited in the sea outside of the ice margin. The same applies for Hjellestad-Milde in Fana, much of Os and Fusa, and not least Halsnøy in Hardangerfjord (*p. R259) and the villages Skånevik (*p. R245) and Etne (*p. R242).

Finally an end to the Ice Age

The most dramatic climatic change we know of in Hordaland, and for that matter in all of Europe, occurred 11,500 years ago, at the end of the Younger Dryas. The Gulf Stream changed course from its direction toward Portugal to instead "gush" into the North Sea with full force over the span of perhaps only 20-50 years. And with it came warmer air. We do not know which was the "chicken" and which was the "egg", but it is certain that the Gulf Stream and the warm south-westerly air reinforced each other, as they do today. Over the course of a hundred years or so, the climate became almost like that of today.

The ice-melt picked up speed. The climatic change took the life of the Scandinavian ice sheet almost instantaneously; every summer more snow melted than fell during the previous winter, all the way up to the highest parts of the glacier. Nonetheless, it still took time for such a thick ice sheet to disappear. If we look to Hardanger fjord, we can imagine that the ice front calved back from Halsnøy to Eidfjord in just 200-400 years. We cannot date the event more precisely than this, but if we think that the 1200 m deep fjord was filled by an ice sheet that inland would reach up to 2,000 m above sea level, we can understand that there were huge volumes of icebergs that sailed out from the coast of Hordaland over the course of a few hundred years; much more than along the East Greenland coast today.

Even though much of the ice sheet calved into large icebergs which first melted when they came out on the ocean, we figure that 10-15 m of ice melted from the lower part of the glacial surface during the summer half of the year. The melting of ice gives nearly as much volume of water as rain, that is, 10,000 - 15,000 mm, expressed in meteorological measures. Today, the annual rainfall is less than 2,000 mm in most parts of Hordaland. It is easy to understand that a volume of water equal to more than 5 times the entire annual rainfall today would give some gigantic, thundering glacial rivers. These carried large quantities of sand and gravel under and alongside of the glacier forward to the ice edge. Nearly all of the sand- and gravel pits in the municipality arise from such glacial-river deposits.

When the glaciers had calved into the deep fjords, they tended to stop when they got solid ground under them. Much of the gravel was therefore deposited as glacial river deltas in the inner fjord areas. Since the land has since risen, we find these deltas roughly 50 - 60, even up to 125 metres above sea level today. They appear as flat terraces that are built up of sand and gravel. In the rainy Hordaland climate they make good agricultural land; in eastern Norway such terraces are dry pine barrens because the rainwater seeps so quickly down in the porous gravel. Geologically, they show both where the glacier front stopped during the ice melt, and how much the land has risen. Such terraces are found in most of the valleys in Hordaland, such as in Modalen, (*p. R428) near the ferry wharf at Kvanndal, in Rosendal, at Odda, Etne (*p. R242) Fana Church, Ulven (*p. R312) and many other places.

The glacier comes alive

Now we might have expected that the glacier would disappear completely and quickly. But nature gives us surprises. In several places we find moraine ridges that show that the glacier in fact made small advances. This can be seen most clearly in the mountain regions of Ulvik - Eidfjord. Continuous, sharp moraine ridges can be mapped here over large distances ( *p. R520) and the glacier can be reconstructed in great detail. A long valley glacier flowed out from Måbødalen, from Fossli to Eidfjord, where the big gravel deposit between Lake Eidfjordvatnet and the fjord was laid down as a delta at the front of this glacier (*p. R516)

Concluding thoughts

Ice ages appeal to fantasy. It is our recent natural history. The first humans who came to Norway saw this great ice sheet. Some youths were probably so curious that they climbed on it. Perhaps they left behind remains of reindeer meat for refrigeration in cracks in the ice. The landscape was different, but not more than that we can imagine glaciers in the fjords, and a higher sea level. Yes, and also a vegetation that resembles more that of mountain regions today. It was different, but nonetheless recognizable. The main features in the landscape were as today. The humans were our forefathers. Animals, trees and flowers that migrated in still have their ancestors living around us. Even though we only know a fragment of the story. Some of the most important finds have been made by amateurs who reported their discoveries to specialists. Use your eyes in nature. Experience its history and report it if you see something exciting.