1. Modelling Magma Intrusion into an Underground Opening Presentation to VOLCANIC ERUPTION MECHANISM MODELING WORKSHOP November 14-16, 2002 University of Hew Hampshire Durham, NH 03824, USA Ed Gaffney and Rick Rauenzahn Los Alamos National Laboratory, Los Alamos, NM 87545, USA

2. Modelling Magma Intrusion into an Underground Opening Ë Context of Yucca Mountain (Ed) –Geologic Setting –Repository Requirements –Potential Igneous Events –Goals of Modelling Ë CFDLIB (Rick) –Background and Basics –Version 02.1 Volatile exsolution Variable viscosity Ë Early results (Ed) –Initial Interactions –Effusive Flow

3. Context of Yucca Mountain Geologic Setting –Fault block in rhyolitic tuff sequence Tertiary Water table ~600 m,repository ~300 m –Pliocene to Pleistocene basaltic eruptions Closest (Lathrop Wells Cone) is 75 ka ~0.15 km 3 Alkali basalt, 2-4 wt/o water

4. Context of Yucca Mountain Repository Requirements –Exposure of target population Over 10,000 year span –Potential hazards Ground water seepage Damage to waste packages from seismic activity Volcanic intrusion

5. Context of Yucca Mountain Potential Igneous Events –Unlikely (10 -8 per year) –Intrusive/extrusive event similar to Lathrop wells alkali basalt 1-4% (wt) H 2 O ~0.1 km 3 –Dike intersects drifts, damages waste packages gas corrosion heat effects on integrity Impact, drag –May erupt to surface fissure, conduit, or dogleg

7. Context of Yucca Mountain Goals of Modelling –Determine environment seen by waste packages Is there a shock from first eruption into drift? Will magma fill drift? Size and velocity of projectiles? Peak environments (P, T, u, dynamic pressure) along drift “Final” environments –Evaluate mechanisms for release Impacts of bombs, other fragments Heating  internal gas P rises  rupture Drag effects (carried to surface, torn by diff. drag forces,...)

8. CFDLIB Background Multiphase compressible and incompressible flows –10 years in development –Test bed for models –Applications in industry, defense Collocated (cell-centered) variables –Fluxing velocities are time-space advanced with pressure correction ICE/MAC –Pressure waves treated implicitly (relax SS Courant condition) –Advection/viscosity explicit –General EOS, multiphase exchange laws (user)

9. CFDLIB Background (cont’d) Particle-in-cell method –Allows mixed Lagrangian/Eulerian treatment –State variables (m, U, x, , …) kept on particles that move with interpolated velocity –Fluid/structure interaction (history-dependent stress laws) Example with rod penetrator

10. CFDLIB Background Elastic Rod Penetrator

11. CFDLIB Background Brittle Rod Penetrator

12. CFDLIB Background YMP special needs Vapor/magma equilibrium –Papale (1997, 1999) –Include air (extend K/J EOS by assuming ideal air) Variable (high) viscosity –Implicit treatment –Model of Shaw (1972) Generalized effective drag/heat transfer –Particle size/coefficients as f(  k,T k,...) Equations of state for gas (BKW) and liquid(U s -U p )

13. Early Results Magma /Tunnel Interaction

15. Early Results Gas Jet A 20 bar gas jet expands into an atmosphere

16. Conclusions Goal: model magma drift interaction CFDLIB is multifluid, multiphase code Mixed Lagrangian/Eulerian facilitates fluid-structure interaction Implicit treatment of pressure waves User supplied equation of state and exchange laws Volatile equilibrium with silicate liquid like Papale but with different equation of state Variable (high) viscosity Work has just begun and team is small magma expansion into drift effusive flow in drift (~ lava tube) gas jet from a circular vent