1. 1 Flow, disintegration and lubrication of clay – sandy debris flows: from the laboratory to the field Anders Elverhøi Fabio De Blasio Dieter Issler Johann Petter Nystuen Peter Gauer Carl B. Harbitz Jeff Marr International Centre for Geohazards Norwegian Geotechnical Institute, Norway Dep. of Geosciences, University of Oslo, Norway. St. Anthony Falls Laboratory, University of Minnesota.

2. 2 SHELF EDGE (STAGING AREA) Storage Capacity Volume of Failure Canyon Positioning relative to delta (sequence stratigraphy) DEPOSITIONAL CONTROLS -Basin Relief -Local Gradient -Evolving Seabed Topography SHELF WIDTH GRADIENT ACCOMODATION SEDIMENTS TRAPS Controls on submarine fan facies distribution Adopted from Statoil, Frode Hadler-Jacobsen

3. 3 What is the origin of deep-water sand bodies? Turbidity currents? (low density, dominant turbulence) Debris flows? (high density, laminar, 1) cohesive? 2) non-cohesive?)

4. 4 Experimental settings St. Anthony Falls Laboratory Experimental Flume: “Fish Tank” Video (regular and high speed) and pore- and total pressure measurements

5. 5 Debris flows- high clay content A: 32.5 wt% clay, hydroplaning front Dilute turbidity current B: 25 wt% clay hydroplaning front D: Behind the head, increasing concentration in overlaying turbidity current

6. 6 Debris flows- low clay content (5%) Turbulente front Deposition of sand

7. 7 Anatomy of a sand-rich experimental debris flow

8. 8 Low clay content – video record Turbidity current Sand waves Dense flow Deposition of sand.

9. 9 Close up pictures/ sand waves High speed video showing: 1)The turbidity current (TC) 2)Debris flow/fluidized layer (DF) 3)Settling layer New layer of sand, stacked sequences? Sand wave

10. 10 High clay content- - Plug flow- “Bingham” High sand content -Macro-viscous flow? -Divergent flow in the shear layer

11. 11 Some examples of velocity field – one image

12. 12 Velocity for the whole flow (proportional to colour) Deposited materials ”Debris flow” Turbidity current Convection cells ? Height [pixel] 1m = 6400 pixel Time [frame] 1 frame = 0.04s Velocity m/s

13. 13 Thickness of sandy deposits – versus clay content

14. 14 Flow behavior: Mass flow at high sand fraction

15. 15 Numerical experiment 1 Transport of a single sand particle through a free surface laminar flow Lift and Drag force Results: a few km runout at most: not an efficient process

16. 16 Fluidized layer: what is its potential for sand transport?

17. 17 Numerical experiment 2 : A simple model for fluidized sand Calculation of settling velocity and runout of an inclined granular bed. Settling is hindered by water expelled from beneath (Richardson-Zaki). The material not yet settled is modeled as a laminar free-surface flow What are the boundary conditions at the top?

18. 18 Numerical experiment 2 Basic equations Richardson-Zaki Viscosity Conservation of particle number Laminar velocity field

19. 19 Example I: Viscosity=0.02 Pa s (  10 x water) Thickness=0.5 m Slope=0.1 degrees Limit velocity=1 cm/s Result: Runout between 400 m and 2 km Results from the calculations Example II Viscosity=0.6 Pa s Thickness=2 m Slope=0.8 degrees Limit velocity=0.2 cm/s Result: Runout between 23 km and 100 km

20. 20 Processes that could potentially improve sand transport in the ocean Turbulence (generally accepted view). Fluidization. Importance of clay, even little clay increases viscosity/improves cohesion  lubricated (hydroplaning) flow Sand waves.

21. 21 Conclusions and future plans CONCLUSIONS Water increases mobility Potential for sand transport in the dense phase 1) sand packed in the clay matrix?) 2) Fluidization? 3) Sand waves? Scaling problems FUTURE PLANS Experiments with different volumes and different grain sizes Direct numerical simulation of high- density fluidization

22. 22

23. 23 Model equations Conservation of particle number Laminar velocity field Viscosity Richardson-Zaki

24. 24 What model for clay-poor debris flows? Some existing models: Savage-Hutter (SH), Norem Irgens Schielthorp (NIS), Iverson Denlinger (ID) Granular: YES Turbulence: NO Macroviscous regime not addressed only in NIS Direct Models ?

25. 25 Prompt disitengration of the debris flow 1) disintegration of the mass: the yield stress drops dramatically 2) settling and stratification solid fraction in the slurry dependent on the clay content Reference solid fraction

26. 26 Existing models: e.g.: NIS model Mud with plug and shear layers –plasticity, viscosity, and visco-elasticity dry friction (no cohesion in code) dynamic shear (thinning) dispersive pressure

27. 27 I-D model Depth integrated, three-dimensional model Accounts for the exchange of fluid between different parts of the slurry due to diffusion and advection. Limitations for our purpose: water content of the slurry must not change, no cohesion, no turbulence