By Willy Fjeldskaar IRIS. Modelling technique Modelling technique Glacial isostasy Iceload data Calibration data Development 2006 Development 2006.

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Presentation transcript:

by Willy Fjeldskaar IRIS

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

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

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

Lithosphere as lowpass filter

Decomposition of ice load

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

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

Nadai, 1950 Equilibrium displacement

Transient displacement Relaxation time The Exponential Decay of Beer Foam

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

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

Uplift history

1) present rate of uplift 2) palaeo shoreline tilt

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 Nm (t e = 20 km) at the Norwegian coast, increasing to more than Nm (t e = 50km) in central parts of Fennoscandia” (Fjeldskaar, 1997) (Fjeldskaar & Cathles, 1991)

Viscosity (10 19 Pa s) Viscosity vs. thickness A uniform mantle viscosity of Pa s.

Observed uplift Best-fit model

Modelling uplift of Svalbard

Bjørnøya Hopen Kongsøya Storøya Wilhelm- øya Sea level changes

Hopen Kongsøya Storøya Wilhelm- øya Sea level changes

A flexural rigidity of 2 x Nm (t e = 25 km) and a uniform mantle viscosity of 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

Crustal thickness

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

Developing model Developing model Implementation Implementation Testing Testing