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Published byHugh Blaisdell Modified about 1 year ago

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by Willy Fjeldskaar IRIS

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Modelling technique Modelling technique Glacial isostasy Iceload data Calibration data Development 2006 Development 2006

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Glacial isostasy The earth’s crust may…be considered as a slowly flexible sheet of solid rock floating on a viscous substratum Nansen, 1928 Nansen, 1928

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A layered viscous Earth with an elastic, uniformly thin lithosphere (Fjeldskaar & Cathles, 1991) Asthenosphere Lithosphere Upper mantle Lower mantle 670km Model

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Lithosphere as lowpass filter

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Decomposition of ice load

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Difference between two timesteps Load removal 20 000 BP 15 000 BP Ice load I(t, k)

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Ice extent and thickness during the last 20 000 years The glaciation rate from one time step to the next is assumed constant

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Nadai, 1950 Equilibrium displacement

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Transient displacement Relaxation time The Exponential Decay of Beer Foam

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Relaxation time wavelengths Filtered relaxation time Relaxation time is the time required for a function to decrease to 1/e (36.8%) of the equilibrium value. Relaxation time

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(40 x 10 23 Nm; 70 km) Order no k = 2 r/ – 1/2 4000 km 400 km Relaxation time

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Uplift history

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1) present rate of uplift 2) palaeo shoreline tilt

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The Earth's response to the deglaciation in Fennoscandia is modelled using a layered viscous model with elastic lithosphere. “The most likely ice model gives a flexural rigidity of 10 23 Nm (t e = 20 km) at the Norwegian coast, increasing to more than 10 24 Nm (t e = 50km) in central parts of Fennoscandia” (Fjeldskaar, 1997) (Fjeldskaar & Cathles, 1991)

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01234567 40 60 80 100 120 140 Viscosity (10 19 Pa s) Viscosity vs. thickness A uniform mantle viscosity of 10 21 Pa s.

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Observed uplift Best-fit model

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Modelling uplift of Svalbard

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Bjørnøya Hopen Kongsøya Storøya Wilhelm- øya Sea level changes

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Hopen Kongsøya Storøya Wilhelm- øya Sea level changes

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A flexural rigidity of 2 x 10 23 Nm (t e = 25 km) and a uniform mantle viscosity of 10 21 Pa s Svalbard rheology The post-glacial shoreline displacement on Svalbard indicates a high viscosity mantle The post-glacial shoreline displacement on Svalbard indicates a high viscosity mantle

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Crustal thickness

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F(k x, k y, t) = e -t (k x,k y )/ (k x, k y ) -1 F(k x, k y, x, y, t) = e -t (k x,k y,x,y )/ (k x,k y,x,y) -1 (k x, k y, x, y) = 1 + D(x, y) k 4 / g Lateral uniform: Lateral varying: (k x, k y ) = 1 + D (k x, k y ) k 4 / g

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Developing model Developing model Implementation Implementation Testing Testing

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