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Berggrunnen i Sunnhordland nord for Hardangerfjorden har sitt opphav i vulkanisme sør for Ekvator for 495 mill. år sidan.
Vulkanismen starta i det gamle Iapetushavet som skilde to av den tidas kontinent, Laurentia og Baltika. Då kontinenta sakte dreiv mot einannan måtte noko breste, og dét skjedde først i den tynne havbotnen mellom dei langt tjukkare kontinental-platene.
Volcanism occurred in the cracks, pushing parts of the seabed aside and under other parts (subduction). Where the seabed was pushed down, majestic, tall volcanoes were built up in a long line over several million years. Sunnhordland's rocks and metals on the north side of the Hardangerfjord originate from this process and these volcanoes.
Men ikkje berre. Kontinenta gav seg ikkje med å lage sprekker og subduksjonar i Iapetushavets botn. Laurentia og Baltika krasja vidare mot einannan til den enorme og 8-9.000 meter høge Kaldonske fjellkjeda, der stein, fjell og leire vart «knøvla» saman for 420 millionar år sidan. Denne kollisjonen var første del av puslespelet som vart til superkontinentet Pangea for 300 millionar år sidan. Fjellkjeda dreiv så sakte nordover på kontinentplatene medan den kollapsa, før Pangea delte seg i nye kontinent og etterkvart forma dagens verdskart. I nordre del av Sunnhordland bur me no på eit fragment av Iapetushavbotnen og dei gamle vulkanane si ufattelege reise. Og bergartene frå Iapetushavets botn, i originalform eller «nykokte», har vist seg særs brukbare gjennom våre nesten 12000 år her på kysten. Kleberstein, grønstein, ryolitt, marmor, klorittskifer, kis, gull, granitt og fylitt har blitt nytta av oss i ulike periodar. Eit så breidt spekter av steintypar, av same opprinnelse og brukt over så lang tid, er hovudargumentet for at Sunnhordland fortener status som UNESCO-Geopark.
Liknande miljø som skapte Sunnhordland for 494-470 mill. år sidan finn du i dag ved Krakatoa-vulkanen i Indonesia.
Eit heilt anna geologisk opphav har berggrunnen på sørsida av Hardangerfjorden. Der bur me på eit fragment av det urgamle Baltika-kontinentet, over 1 milliard år eldre enn dei vulkanske bergartene frå lavastraumane i Iapetushavet. Granittane i Ulvanosi er 1,2 milliard år eldre enn granittane på Bømlo, Fitjar, Tysnes og Austevoll, og både den og dei andre bergartene på den sida av fjorden har vist seg mindre eigna til redskap for oss.
I det litt mjukare «arret» mellom Iapetus-havbotn og Baltika-berggrunn har så 30-40 istider, med enorme brear i stødig sig ut mot havet, grove ut Hardangerfjorden, ein av verdas lengste, djupaste og vakraste fjordar. Dalane, fjellsidene, morenane, jettegrytene og øyarkipelet er óg prega av desse tunge landskapsformarane sitt arbeid gjennom dei siste 2,6 millionar åra. Dette landskapet har igjen prega oss, som fjell-, fjord- og sjøvande kulturfolk.
Putelavafeltet på Finnås – dei 495 millionar år gamle fødselsmerka til Sunnhordland.
Grønsteins-øksene frå Hespriholmen var identitetsmerket for steinaldermenneska mellom Sognefjorden og Lista i meir enn 6000 år.
Rock types
Granite
Granitt er ein magmatisk bergart som består av kvarts, feltspat og glimmer, og er ei steinsmelte som eingong størkna på store djup. Spesiell eigenskap er at den ganske lett kan delast i tre retningar (anisotrop). Granitt er brukt til brustein, byggestein og monument, spesielt rundt århundre-skiftet 18-1900 då nasjonalkjensla var ekstra høg. Granitten vart rekna som «den norske» bergarten.
In the entire northern part of Bømlo, Fitjar and Austevoll, granite is the dominant rock. Extraction of granite began on Rubbestadneset in 1863 when Swedish sluices had been commissioned to extract stone here at Skoltegrunnsmoloen in Bergen. This started an industry that eventually involved many local villagers.
Until the end of the 1940s, it was Sunnhordlanders who at times lived off stonework. "Bergen built with bømlogranite" it says in a headline in The Naturhistorisk Vegbok (The book of Nature historical roads). The title refers to both the soapstone in the medieval churches and to the granite in Kjøttbasaren in Bergen, the large blocks in the front on Bryggen in Bergen, Sandvikskirken and a lot of cobblestones, stairs and curbs in the city. All this comes from Sunnhordland and especially Bømlo.
Locally in Bømlo and Fitjar, the stories of the Finn "Taipen" (Taipale) and the travellers Håkon and Knut Urangsæter who carved stone and made the most beautiful walls, quays, stairs and gravestones are still alive. The walls remain as eternal monuments, and in the outlying areas of Sunnhordland's granite municipalities there are long, beautiful stone gardens that have been built and rebuilt by travelling men in exchange for room and board outside the fishing season.
Right Martines Haldorsen from Rubbestadneset tells about his meeting with the Swedish sluices in 1863, in a unique audio recording from 1938. Martines was a blacksmith on Rubbestadneset in the 1880s after learning the art of blacksmithing from Swedish granite sluices.
In Martine's forge, the 18-year-old son Haldor made the first Wichmann engine in the winter of 1902-‘03, the engine that was to dominate the motorization of the Norwegian fishing fleet.
Unique sound recording from 1938
Greenstone
Greenstone is a massive metamorphic rock formed by the remelting of volcanic rocks such as basalt and diabase at relatively low temperatures. The green color is due to mineral chlorite, actinolite and epidote.
The quarry on Hespriholmen is a unique monument from the world's Stone Age culture. Ax material was fired here for a period of almost six thousand years (9500-3500 BC), and greenstone axes from Hespriholmen were during this period the identity mark for humans in southwestern Norway, I.E. between Lista in the south and Sognefjorden in the north. The quarry is considered the longest-running "industrial enterprise" in the world.
The stone was transported by boat from Hespriholmen to the Sokkamyro workshop site in Langevåg. At first, the axes were processed in the same way as flint axes, i.e. by cutting off pieces until the shape was reasonably close to the desired shape. Later, the stonemasons in Sokkamyro developed a new production method in which the pieces were "dot-cut" into a narrow, perfect elliptical shape and given a sharpened edge on one side.
Greenstone is found in several places on Bømlo, but it is only on the weathered Hespriholmen and in a small quarry on the west side of Siggjo (Stegahaugen) that it has been mined. This probably indicates that the stone here is of particularly good quality, but it may also have had mythological reasons.
In addition to being tools for woodworking, the axes may have had ritual or symbolic values. It is also natural to think that both subjects and finished axes were useful as a medium of exchange / currency.
Vespestad axe.
Carved step axe (drawings: Sigmund Alsaker)
Gold
One hypothesis is that gold came to Earth with meteorites 4 billion years ago and was concentrated in visible amounts through volcanism on the ocean floor. In Sunnhordland, like many other places, you can find gold in or in layers with quartz.
(Aurum / Au), metallic element with atomic number 79. Gold is not affected by other substances / acids, but binds to mercury. 1 liter of gold weighs about 20 kg.
In 1862, a shepherd boy found the first gold nugget at Lykling. From 1882-1910, gold mining was carried out on a large scale along the quartz veins in Lyklingeberga, with a total of about 300 men employed at most and a total gold catch of about 200 kilos. Three large companies, mainly financed and run by Englishmen, but also a number of "one-man businesses", changed the face of the small village during the 25 years or so that the mining operations lasted.
Two hotels, a hotel ship, several bakeries and a number of shops of various kinds were built around mining. The mines at Lykling are the largest gold mines in the country, even though more gold has been found as a by-product in the ironworks in Bidjovagge in Finnmark.
Gold is still found on Lykling, but the area is protected so that it is not allowed to bring stone or gold from the area without an agreement with the licensee.
SULFIDE MINERALS
Kopar og svovelkis oppstår i langsomme prosessar (black smokers) ved undersjøisk vulkanisme. Kis frå det gamle Iapetushavet er utvunne i Sunnhordland i periodar frå 1860 til 1968, og la grunnlaget for storstilt industri på Litlabø.
Pyrite mine in Dyråsen, Ølve.
At Bømlo, it was the deposits on Lindøy (pyrite) and Alvsvåg (copperite) that proved rich enough for ordinary operation of some extent. On Varaldsøy, there was operation in Varaldsø Mining Company Ltd until the end of the 19th century, as well as in some later periods (e.g. the First World War). In the first period, the English family Barrat were both owners and operators of the mine, where the son Thomas later was the founder of the Pentecostal Church in Norway.
Copper ore was a raw material for the precious coin metal copper (Cu), while sulfur ore was a raw material for sulfur, an increasingly sought-after ingredient in medicine and industry (sulfuric acid) as well as ammunition and dynamite after the 19th century.
Sulfur pyrite (FeS2) consists of iron and sulfur and belongs to the mineral group sulphides. The kis itself is a glossy brass color and the stone around a strong sulfur color. Coparkis (CuFeS2) is a sulphide mineral and the most important copper mineral in Norway. Copper ice is yellower than pyrite and can be scratched with a knife. It oxidizes with turquoise color. The rust color comes from oxidized iron (Fe) which is found in both types of coffin.
At Karmøy (in Sunnhordland's neighboring region), the copper arch deposits laid the foundation for what was to become one of northern Europe's largest copper works at the end of the 19th century. 70% of the Norwegian export revenues then came from the copper plant at Vigsnes. At Litlabø on Stord, the local community on Litlabø grew in step with the Pyritemine Stordø, which under German owners from the early 1900s m.a. produced sulfur for the cellulose industry in Europe. Locally in Sunnhordland were rust-colored gravel from the production at Litlabø, «macadam», a very useful product in road construction etc.
Stordø Kisgruber, under the auspices of Venelaget, has become a visitor mine of the very rare. Both production premises, office buildings, travel cupboards, mining tunnels, a transport train and a dwelling house have been restored and are available for guided tours. In total, there are about 90 km of mining tunnels on Litlabø, with the deepest mining tunnels 700 meters below ground level. The community that was built around the mining industry stood out from the rest of the Stordsamfunnet, and when the mines were closed in 1968, labor from here was important for the growing shipbuilding industry on the island, both on the "floor" and in the engineering offices.
Sulphidic minerals working group in Dalen, anno 1911.
SOAPSTONE
Kleber er ein omdanna bergart som består av talk, serpentin og magnesitt. Det er naturens mjukaste bergart, kan skjerast i og tåler varme utan å sprekke. Er nytta til pudder, gryter, spinnehjul, søkkjer, ovnar, byggestein og skulpturar.
Hordaland's largest soapstone quarry can be found at Lykling, Bømlo. Here it was probably first to take out stone blanks for urns and pots (grjotstein »), sinks and weights from the Neolithic, but it is as a source of block stone for the medieval churches in Bergen that Austavindhaugen on Lykling is best known. "Squares" are blocks of approx. 1 × 0.5 × 0.5 meters.
It is also useful soapstone from Lykling in Mostrakyrkja, built approx. 1100, but then as botnsville under the coffin wall as well as some places in the wall itself. It is uncertain whether Mostrakyrkja was built before or after the medieval churches in Bergen (Korskirken, Domkirken, Mariakirken and Nonneseter Kloster).
There are no sources today that tell us who operated the quarry here in the Middle Ages. It may have been local labourers who learned the technique abroad or from foreigners, perhaps in connection with the construction of Mostra Church. If you walk over the hill and along the rock face of Austavindshaugen today, you will come across piles of waste from the production. In the rock face you will notice that a number of blocks stand like large Lego bricks, more or less ready to be chiselled out. If you listen carefully on a quiet evening, you might still be able to hear the hammering, laughing and chatting... And at the jetties along the beach, you might be able to make out the sailing ships with the busy jetties outside. In the 12th to 13th centuries there was certainly a lot of hustle and bustle here!
Soapstone is the softest rock we have, and is a metamorphic rock consisting mainly of the mineral talc with varying amounts of chlorite and amphibole. It is very heat-resistant.
The professional community is on sight experience in the soapstone quarry at Lykling.
Marble
Marmor er ein omdanna kalkstein som hovudsakleg består av mineralet kalsitt (CaCO3). Kalksteinen er opprinneleg restar etter tjukke lag av døde kalkalger på havbotnen som etterkvart vart pressa saman.
From the construction of Mostra church in the 1000s, we have broken out marble in Sunnhordland, both for lime cement and building blocks.
«Søndhordlehn is known for its marble species, the most beautiful in the country». Topographical-Statistical Description of Norway», J. Kraft, 1829
Ever since the 11th century and the construction of Mostrakyrkja, marble has been broken out on Moster, somewhat later on the small island of Hidle between Stord and Halsnøy and on Storsøy just north of Huglo. Locally, marble prefers to be called «kalkstein»(Limestone) or «limstein»(Gluestone). Since marble is metamorphic limestone, ie it is heated an extra time and has become more crystallized, it works just as well as a raw material for limestone burning as the softer limestone. The content is the same; amounts of calcareous algae that have sunk to the bottom and formed thick sediments that over time and pressure have turned to rock (CaCO3).
The marble in Sunnhordland has first and foremost for almost 1000 years been used as a raw material for the production of lime cement a necessary ingredient e.g. in the coffin wall of Mostrakyrkjas.
For about 120 years from the early 18th century, however, beautiful marble blocks were exported to the Danish-Norwegian king's castle and monument in Copenhagen and the Caribbean (St. Croix).
The person responsible for these exports was first "den grusomme Montanjen", then the Finn priest Peder Harboe Herzberg who excelled as a great enlightener for the people in both the region and the country.
On the streets of Copenhagen you walk on marble from Sunnhordland.
In the 20th century, much of the marble, especially from Moster, was useful as a raw material in the industrial production of carbide at Odda Smelter and ferrosilicate and silicon at Bjølvefossen in Ålvik. Until 1969, however, burnt lime was sold both as fertilizer in Hardanger and as a binder in burning bricks etc in the Sandnes area.
From the end of the 19th century, the marble mines laid the foundation for a freight boat industry which in the 1960s counted 75 boats based on Moster. Most of the family then owned a boat that went with lime and marble crushed stone or other freight on a route along the coast.
Moster Amfi is in a disused marble mine, and marble is easy to find both around the amphitheater and other places on Moster, e.g. in Notlandsvågen.
Marble is a metamorphic rock that mainly consists of the mineral calcite (CaCO3).
Rhyolite
Ryolite is a volcanic rock that consists of the same mineral as granite, but since ryolite often solidifies on the earth's surface during volcanic eruptions, the mineral grains are smaller. In Sunnhordland, the rhyolite originates from the eruption of volcanic archipelagos 470 million years ago.
Five or six thousand years ago, people on Siggjo made arrowheads for their hunting bows from these ancient lava flows.
Take a trip to the rhyolite quarry next time you are at Siggjo. Imagine that people sat here five thousand years ago and made arrowheads for their hunting books, arrows that have been found all the way north in Trøndelag! The quarry is on a hillside just west of the pond at the northern end of Siggjatoppen.
The city was ideal in many ways; here the rhyolite was glassy and perfect for arrowheads, and in the pond just above they could fetch water in leather sacks to empty on the rock which they first heated with an oak fire. The large drop in temperature in the stone then did its part to cause the rock to crack into planed blanks, and which they further processed there on the hillside. The remnants of the arrowhead production can be found in the heather if you look!
The ryolite on Siggjo is a fine-grained rock formed by explosive volcanism 470 million years ago. It has sharp breaking edges and was used for arrowheads in the period 5000-4500 before the present (approx.).
Pillow lava
På Finnås finn du fødselsmerka frå då berggrunnen vår dukka opp i havbotnen sør for Ekvator. Lavaen strøymde ut på havbotnen for 495 millionar år sidan, og størkna som puter i møtet med det kalde sjøvatnet. Putene er seinare slipt ned til den overflata dei har på Helgeneset på Finnås.
The Pillow lava field at Finnås is one of the most spectacular geo-localities in Geopark Sunnhordland.
This lava part, which once broke up at the bottom of the ancient Iapetus sea, happened when the ancient continents Laurentia and Baltika drifted towards each other on their way to the creation of the huge Caledonian mountain range. The thinner seabed between Laurentia and Baltika cracked due to. the pressure, and one side was pressed down under the other. Lava bubbles pushed up from the earth's interior through the cracks, and solidified into "sausages" in the encounter with the seawater.
Originally, the surface was "sausage" or "bubbling", but is now sanded down to a relatively smooth surface and seen on a high edge. Remember that this party has followed the 8-9,000 meter high Caledonian mountain range that sails on the continental plate mostly from the South Pole and up to us. It has really run its course, and been sharpened, turned and turned!
These processes take place continuously out in the oceans, as the continents are constantly moving towards or from one another. The soil changes, a few cm per. years but over huge time spans. The pillow lava field at Finnås is a reminder of the unimaginable transformation our landscape is a result of. And after the pillow lava party found its place where it is now, it has been refined and polished by 30-40 ice ages over the last 2.6 million years (the Quaternary period).
Greenschist
Volcanic ash from the Iapetus sea was a source of freshly baked flatbread. Ølve supplied Norway and the North Sea islands with baking trays in the Middle Ages.
Chlorite shist is a type of soapstone, "easy" to chop into baking slabs, but unsuitable for pots.
The geological origin of the chlorite shist dates back to the time when Norway lay south of the equator. Submarine volcanism created volcanic islands in the ocean between "Norway and Greenland" (Baltica and Laurentia).
The geological origin of the chlorite shist dates back to the time when Norway lay south of the equator. Submarine volcanism created volcanic islands in the ocean between "Norway and Greenland" (Baltica and Laurentia).
Igneous Breccia
På toppen av Grutle-brekka på Bømlo kan du sjå spor av spektakulære lavastraumar, tilsvarande dei raudglødande straumane me i dag kan sjå på Hawaii. På Grutle er dei kolna og over 470 millionar år gamle. Breksje vert danna når lavastraumen storknar på utsida men framleis er flytande inni. Dei storkna partia ytst vert brotne opp (breksjert) og fell tilbake i lavaen som lysare bitar.
Tekst om lavabreksje.