Geological surveys at Hoven in Loen, Stryn municipality June 2014 Project information and status: Document title: Geological surveys at Hoven in Loen, Stryn municipality Document number: Contract number: Project: 2014-03-010B Classification: Distribution: Internal Date of deliverance: Status: Pages: 12th of June 2014 Completed 36 Contractor: Contractor information: Sunnfjord Geo Consulting AS Villabyen 3 6984 Stongfjorden Organization number: 998 899 834 MVA Contractor contact information: Client information: Sunnfjord Geo Consulting AS SleipnerHoven Loen AS Synne Lindgren Alsaker v/Richard Grov Manager 6789 Loen Villabyen 3, 6984 Stongfjorden Tel.: 928 92 969 e-mail: [email protected] [email protected] Dicipline: Document type: Location: Geology Report Loen, Stryn municipality Fieldwork executed by: Executed (Date): Signature: Synne L. Alsaker 23rd and 24th of May 2014 Synne L. Alsaker (sign.) Einar Alsaker 23rd and 24th of May 2014 Einar Alsaker (sign.) Atle Nesje 23rd and 24th of May 2014 Atle Nesje (sign.) Even Vie 23rd and 24th of May 2014 Even Vie (sign.) Tor Ivar Birkeland 23rd and 24th of May 2014 Torkjell Ljone 23rd and 24th of May 2014 Anders Haaland 23rd and 24th of May 2014 Siri Anne Haugland Strand 23rd and 24th of May 2014 Report written by: Report completed (Date): Signature: Even Vie 6th of June 2014 Even Vie (sign.) Report reviewed by: Report approved (Date): Signature: Einar Alsaker (Technical advisor) 10th of June 2014 Einar Alsaker (sign.) Atle Nesje (Technical supervisor) 7th of June 2014 Atle Nesje (sign.) Report approved by: Approved (Date) Signature: Synne L. Alsaker (Manager) 12th of June 2014 Synne L. Alsaker (sign.) INDEX INTRODUCTION .................................................................................................................... 3 ABSTRACT .............................................................................................................................. 4 CHAPTER 1 – DESCRIPTION OF FIELD AREA ............................................................. 5 1.1. Location .......................................................................................................................... 5 1.2. Topography, vegetation and hydrology ....................................................................... 6 1.3. Climate ............................................................................................................................ 6 CHAPTER 2 – GEOLOGY ..................................................................................................... 7 2.1. Bedrock geology ............................................................................................................. 7 2.2. Quaternary geology ....................................................................................................... 8 CHAPTER 3 – OBSERVATIONS .......................................................................................... 9 3.1. Internal observations: mapping of structural orientations in the bedrock .............. 9 3.2. External observations: earthquake history in the field area ................................... 29 CHAPTER 4 – INTERPRETATIONS ................................................................................. 31 4.1. Structural mapping of the field area .......................................................................... 31 CHAPTER 5 – SUGGESTIONS TO PREVENTIVE ACTIONS ..................................... 33 CHAPTER 6 – CONCLUSION ............................................................................................ 35 KAPITTEL 7 – REFERENCES ........................................................................................... 36 ATTACHMENTS ...................................................................................................................... I ATTACHMENT I – CLIMATE ............................................................................................ II Climate statistics .................................................................................................................. II Climate prognoses ............................................................................................................. VII 2 INTRODUCTION SleipnerHoven Loen AS contacted Sunnfjord Geo Consulting AS (SGC) to perform a geological survey at the site of a planned cable line, mast and mountain station at the mountain Hoven in Loen, Stryn municipality, Sogn og Fjordane county. The main task is to assess the stability of the bedrock where the buildings will be placed, and to illuminate the risk of rockslides in the area. The fieldwork was executed the 23rd and 24th of May 2014, by seven geologists and one administrator from SGC. The result from these investigations is supplied by data from The Geological Survey of Norway (NGU), the Norwegian Meterological Institute, the federal mapping agency Statens kartverk and technical literature. The report is divided into seven chapters, where Chapter 1 and 2 constitute an introduction to the area, Chapter 3 presents our own and external observations/results and Chapter 4 and 5 presents our interpretations, discussion and suggestions. Chapter 6 and 7 is our summarized conclusion and references, respectively. In general, it is the field observations that make the basis of our conclusions, and external information is only used as an important supplement to these. Only the geological aspects of the project and the area are treated here. All conclusions we make assume that human intervention could potentially change the geological and hydrological conditions, and thereby also the risk of rockslides and other hazards. If our results show that there is a risk of geohazards in the area, SGC will suggest preventive actions to avoid this (Chapter 5). SGC has a third level authorization within geotechnical consultancy from the Norwegian ministry of construction (Sentral godkjenning i tiltaksklasse 3, Direktoratet for byggkvalitet) and is therefore qualified to suggest such preventive actions. However, the final decision and responsibility for this lays at the project leader/owner. We can still provide the client with geotechnical consultancy throughout the entire construction process. 3 ABSTRACT Sunnfjord Geo Consulting AS (SGC) has performed a geological survey at the site of a planned cable line, mast and mountain station at the mountain Hoven in Loen, Stryn municipality, Sogn og Fjordane county. The investigated area is located at around 1000-1008 m a.s.l., around the mountain Hoven in Loen Stryn municipality, Sogn og Fjordane county. The area is an isolated hill on the southern side of the mountain Staurinibba (1349 m a.s.l.). Between Hoven and the mountain area behind there is a shallow valley. In the south, Hoven is abruptly terminated by a several hundred metre high, vertical cliff, facing south towards Nordfjorden (Lobukta). The vegetation on Hoven is dominated by heathland, and there are no rivers within the field area. The bedrock consists of quartz monsonite and the ground is covered by till. Major talus deposits are mapped at the southern foot of the mountain. During the fieldwork, the orientation of joints or lineaments (joints, fractures and faults) and foliation was measured on several locations on and around Hoven, with regard to the bedrock stability. Three main linement directions were mapped, JD#1, JD#2 and JD#3. JD#1 is dipping down in southward directions, making a plane that may favour rock fall. JD#2 is more-or-less perpendicular to this, and causes the foliated monzonite to be fragmented in blocks. SGC has also been going through the earthquake history from the area. This indicates that earthquakes will have no influence on the rock fall/-slide hazard potential at Hoven. The nature of the joints and the earthquake history indicate that there is no risk of major rockslide events in the area, but our results indicate that there is a certain risk of a more long- term undermining of the planned buildings at Hoven. To avoid negative consequences on the planned buildings we suggest to locate the planned cable mast as far into the plateau as practically possible. Likewise it should be anchored as far north as possible, to reduce the strain along the most critical joint direction (JD#1). All work with explosives close to the planned lots should be kept at a minimum, and preferably finished before the start of construction work. For the same reason, we also suggest to place the planned intra-mountain storage halls on the north side of the valley depression north of Hoven. 4 CHAPTER 1 – DESCRIPTION OF FIELD AREA 1.1. Location The field area is around the mountain Hoven (1008 m a.s.l.) in Loen, Stryn municipality, Sogn og Fjordane county. This is a part of the mountain area adjacent to the inner part of Nordfjorden. Loen is the closest village, located to southwest of the investigated area. The cable mast and the mountain station is planned on a ledge, some tens of meters south/southeast of the highest point at Hoven. Figure 1: Map over the field area. The mountain Hoven is located at the north side of the inner part of Nordfjorden. Loen to the southwest is the closest village. Based on map from Statens kartverk. 5 1.2. Topography, vegetation and hydrology Hoven is a mountain area at 1008 m a.s.l., on the south side of the higher mountain Skredfjellet, at 1155 m a.s.l. The southern limitation of Hoven is a steep cliff with a vertical, several hundred meter high wall, before the slope decreases slightly into the fjord. From Hoven and northwards, the topography is sloping