1. by Willy Fjeldskaar IRIS

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

3. 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

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

7. Lithosphere as lowpass filter

8. Decomposition of ice load

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

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

13. Nadai, 1950 Equilibrium displacement

14. Transient displacement Relaxation time The Exponential Decay of Beer Foam

15. 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

16. (40 x 10 23 Nm; 70 km) Order no k = 2  r/ – 1/2 4000 km 400 km Relaxation time

18. Uplift history

19. 1) present rate of uplift 2) palaeo shoreline tilt

20. 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)

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

22. Observed uplift Best-fit model

23. Modelling uplift of Svalbard

24. Bjørnøya Hopen Kongsøya Storøya Wilhelm- øya Sea level changes

25. Hopen Kongsøya Storøya Wilhelm- øya Sea level changes

26. 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

27. Crustal thickness

29. 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

30. Developing model Developing model Implementation Implementation Testing Testing