The Fjords – beautiful and dangerous

L.H. Blikra, Geological Survey of / International Centre for Geohazards Tafjorden, 1934 Tafjord 1934 (3 mill. m3): 60 m high tsunamis Loen after the september 13th event, 1936. Volume: 1 mill. m3; Tsunami: max. 74 m Future?

After the Loen disaster in 1936 NGU was asked by the Ministry for Internal affairs to investigate the treat caused byyg large rockslides There are still numerous “ghosts”along the Norwegian fjords

“Fjord interests”

• Inhabitants • Industry ••InInfrastructure ••TourismTourism How can we handle this treat and help to create safe and strong communities? Key issue: Knowledge

• Hazard mapping and analysis • Handling of high-risk objects (e.g. Monitoring & Early Warning) Hazard: Knowledge about landscape evolution is the key • Rockslide events (distribution and chronology) • Source areas (fractures, structures, active movements….) Some key data for hazard analysis: • LIDAR – onshore • High-resolution bathymetri • InSAR for movement detection Fjord data Z

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B 300 m A Geirangerfjord slides 20 m

5000 – 1000 C14 BP 8000 – 5000 C14 BP 10000 – 9000 C14 BP 11000 – 10000 C14 BP NGU 0004020 Source area Stranda

Foliation

Tafjord

Hellesylt Illustrasjon: NGU West side of Tafjorden Potential large rockslope failures in Møre & county

Molde

Sunndalen Ålesund

Romsdalen Stranda

Geiranger Investigations of active movements is an important part of a hazard program (E.g. GPS, InSAR)

Risk classes: Classificaton of risk objects Class 6 Class 5 Class 4 Class 3

Opstadhornet

Sunndalen Ålesund

Stranda Romsdalen

Tafjorden

Åknes Einar Anda Åknes rockslide

Initiated as an earlyearly--warningwarning project in 2004 Main aim for investigations:investigations: 3D ggyeometry and behaviour of ustable area

1010--1414 mill. m3

30-40 mill. m 3 Upper laser

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Movement Deformation model

How deep is the slide????

Instrumentation in boreholes: Sensors that measure movement and pore pressure Movement in upper borehole: Below 100 m depth

100 m pth ee D Waterlevel upper borehole 1 March – April 30 Early-warning system is based on: • Surface movement • Subsurface movements •Seismic activity • Pore-pressure • WhWeather station Monitoring systems

Total station (robot) Distance to 30 prisms

Large practical & scentific challenges: •Snow • Snow creep • Snow avalanches • Rock fall • Fjord s - large atmosphilherical changes • Large distances • Availability – helicopter • Power, communication The Fjords – beautiful and dangerous

The GiGeoscience have the knowledge and thltechnology to cope with these challenges The Surveys present role(and responsibility..)responsibility..) • Hazard assessments (coordination (coordination,, qualityquality)) • ”DeliverDeliver”” and recommendhandlin g of highh--riskrisk objects ((wellwell documenteddocumented)) • Manage data (geology(geology,, hazardhazard,, monitoring)monitoring)