Geological excursion to Bohuslän
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September 25, 2022
in Excursions, Nature

Geological excursion to Bohuslän

This weekend, geologist Thomas Eliasson from the Swedish Geological Survey (SGU) arranged the annual Autumn excursion to the spectacular landscape of Bohuslän’s granites. We met around 9:30 and we brought our two dogs with us. At age nearly 6 months, Jörfi took part in this her first geological excursion and really enjoyed it! She is already very obedient and we could have her without a leash in many places and I guess she covered twice the distance as the rest of us, because she was running back and forth all the time. To not exhaust her completely, Erik and I decided to stop earlier than the other participants and drove to the island Orust for a late lunch at Bengt Liljebladh’s place. Thanks to Bengt and neighbour Susanne for providing us and the dogs with food when we were all so hungry after the excursion.

Here follows Erik’s more detailed description of the excursion:

An autumn excursion to the Bohus batholith

The last weekend in September we joined a group of granite lovers for a one-day excursion to the 925 Ma Bohus batholith. A small but rock-solid group have formed the informal “granite coast” group with the core members; Thomas, Jesper, Mats, Johan, Peter, Assen and Kjell. During the recent years I have managed to intrude this group. They called to an excursion on the 24th of September and Gabrielle and me was invited. We set out from Gothenburg at eight o’´clock and arrived at the rendezvous point at an art shop (Konstnärernas Kollektivverkstad Bohuslän) near Bovallstrand (≈3km) at 9:30. We started to visit the old quarry in Bovallstrand there it is a coarse grained red Bohusgranite. It is from this quarry the building material was delivered to the Vasa church in Gothenburg. We returned to the art shop and hiked to a narrow and deep crack that runs through the granite. Before we entered people checked the map on the cells (fig. 1). The crack is about 200 long and no fine-grained material is left, only blocks (Fig. 2). It is a challenge to get through under and over the blocks (fig. 3). All the blocks that are wedged in the narrow crack and they are well rounded and experienced high energy transport (fig. 4). It has been high flow rates of the water removing all fine material in the crack. The blocks are hanging in the crack and are apparently well wedged so hopefully the excursion leader (Thomas) should not be worried (fig. 5). The group have emerged from the crack out in the open (fig. 6). After a cup of coffee at the art shop we continued to the 12-cetury church at Svenneby. The last stop for the excursion was the Valön nature reserve with a fantastic granite landscape. The dogs enjoyed the cliffs (fig. 7) and was tired when we got home. We left the grout at the sea (fig. 8) after a fantastic day – thank you Thomas for the excursion.

Figure 1. From left; Thomas, Johan, Assen and Jesper all checking the cell before entering the crack in the mountain. Photo: Erik Sturkell.
Figure 2. Jesper standing in the crack with only the coarse-grained fractions left. Photo: Erik Sturkell.
Figure 3. It takes some dextrality to get through the crack. Photo: Erik Sturkell.
Figure 4. A block wedged high up in the crack. Photo: Erik Sturkell.
Figure 5. Can Thomas be worried about the blocks hanging in the crack? Photo: Erik Sturkell.
Figure 6. Johan, Thomas, Jesper, Mats and Kjell Helge emerging out in the open from the confirmed space of the crack. Photo: Erik Sturkell.
Figure 7. Gabrielle with the dog’s Deli and Jörfí at Valön nature reserve. Photo: Erik Sturkell.
Figure 8. We are leaving the group at the coastline at Valön nature reserve in the granite terrain. Photo: Erik Sturkell.
Photo: Gabrielle. Thomas explaining the details of this place we are visiting as the first stop.
Photo: Gabrielle. A black Permian dike in the red Bohus Granite.
Gabrielle: Jörfi running back and forth on the walking path of Bovallstrand.
Photo: Gabrielle. A group of senior men all looking at a screen of a cellphone.
Photo: Gabrielle. The old church in Svenneby.
Photo: Gabrielle. Erik at the church in Svenneby.
Photo: Gabrielle. Arriving at the nature reserve on Valön.
Photo: Gabrielle. The impressive red granite landscape along the west coast in Bohuslän.
Photo: Gabrielle. Erik and the dogs on Valön.
Photo: Gabrielle. Red Bohus granite on Valön.
Photo: Gabrielle. And luckily food at Bengt’s place on Orust.