Titan2D Simulated Debris Flow Hazards: Arequipa, Peru

1
Titan2D Simulated Debris Flow Hazards Arequipa,
Peru

• Adam J. Stinton1, Gwenaël Delaite2, Brett
  Burkett1, Michael Sheridan1, Jean Claude Thouret2
  and Abani Patra3
• 1Department of Geology, University at Buffalo,
  Buffalo, NY, USA
• 2Laboratoire Magmas et Volcans, Université Blaise
  Pascal, Clermont-Ferrand, France
• 3Department of Mechanical and Aerospace
  Engineering, University at Buffalo, Buffalo, NY,
  USA

2
Overview

• Background Why model volcanic debris flows?
• Laharz.
• Titan2D.
• Model applications and results.

3
Background

• We model to
• Better understand DF behaviour
• Develop better mitigation plans
• To prevent another Armero

4
Laharz
Iverson et al, 1998 Schilling, 1998

• Simulates volcanic debris flows only.
• Statistical analysis of debris flow deposits.
• Run in a series of Arc/Info AMLs scripts.

5
Titan2D
Pitman et al., 2000, Sheridan et al., in press

• Depth-averaged, thin-layer granular-flow.
• Incompressible Coulomb flow.
• Conservation equations for mass and momentum
  solved with a Coulomb-type friction term at the
  basal interface.

6
Titan2D

• Governing equations are solved using a parallel,
  adaptive mesh, Godunov scheme.
• Geophysical mass flows are long and thin (small
  variations of the variables in the normal
  direction).
• Complexity implied by the 3D model is avoided.

7
Titan2D

• Field data suggests sliding takes place on a thin
  basal layer (velocity and density variations
  confined to the basal layer).
• Allows assumption of constant density.
• Simple treatment of Coulomb stresses.

8
Titan2D

• 2D - depth averaged equations
• continuity
• x momentum
• Gravitational driving force.
• Momentum due to erosion.
• Resisting force due to Coulomb friction at the
  base.
• Intergranular Coulomb force due to velocity
  gradients normal to the direction of flow.

1
2
4
3
9
Titan2D

• Can be run on laptops to supercomputers.
• GRASS GIS for the topography and material
  properties data.

10
Arequipa, Peru

• City of 1 million people.
• 17 km southwest of summit of El Misti.
• Undergone dramatic and largely uncontrolled urban
  expansion.
• New settlements being built closer to volcano.

11
El Misti viewed from downtown Arequipa
12
El Misti, Peru

• Eruption and/or rainfall-triggered debris flows
  have occurred in the Holocene.
• Summit snowfield area is 1 to 7 km2.
• 2.5 x 106 m3 of meltwater available.
• Channeled debris flows in the range of 4-5 x 106
  m3, and as high as 11 x 106 m3.

13
Results

• Overall, good results achieved.
• Some significant differences can be seen.
• Flow behaviour is better simulated with Titan2D.
• Run out distance is shorter with Titan2D.

14
Results
15
Results Superelevation
Rio CHili
16
Results Flow Divergence
Pyroclastic flow deposit island in valley
Q. San Lazaro
17
Results Uphill Flow
Q. Agua Salada
18
Results Overbanking
Q. Huarangal
19
Conclusions

• TITAN2D simulations were always shorter than
  those from Laharz.
• Several features of debris flows clearly
  identified in the Titan2D simulations.
• Titan2D is more responsive to the underlying
  topography.
• Forthcoming additions to Titan2D will improve the
  accuracy of the simulations.

20
References

• Iverson, R.M., Schilling, S.P., Vallance, J.W.
  1998. Objective delineation of lahar-inundation
  hazard zones, Bull. Geol. Soc. Amer., 110, pp.
  972-984.
• Pitman, E.B., Patra, A., Bauer, A., Nichita, C.,
  Sheridan, M. and Bursik, M. 2003. Computing
  debris flows. Physics of Fluids 15, pp.
  3638-3646.
• Schilling, S.P. 1998. LAHARZ GIS program for
  automated mapping of lahar-inundation hazard
  zones, USGS, open-file report, 98-638.
• Sheridan, M. F., Stinton, A.J, Patra, A., Pitman
  E. B., Bauer, A. and Nichita, C.C. Evaluating
  TITAN2D mass-flow model using 1963 Little Tahoma
  Peak avalanches, Mount Rainier Washington, J.
  Volcanol. Geotherm. Res., to appear.

21
Questions?