**-i**- Print input data
**-m**- Print memory usage requirements
**--overwrite**- Allow output files to overwrite existing files
**--help**- Print usage summary
**--verbose**- Verbose module output
**--quiet**- Quiet module output
**--ui**- Force launching GUI dialog

**elev**=*string***[required]**- Name of elevation raster map
**h_ini**=*string***[required]**- Name of landslide initial body thickness raster map
**fluiddist**=*string***[required]**- Name of distance from the landlide toe raster map
**rheology**=*string***[required]**- Name of rheological law
- Options:
*frictional, Voellmy, viscoplastic* **rho**=*float*- Density of the flow [Kg/m3]. Required only for viscous rheologies.
**ystress**=*float*- Apparent yield stress [Pa]. Used only for viscous rheologies (optional).
**visco**=*float*- Dynamic viscosity [Pa*s]. Required only for viscous rheologies
**chezy**=*float*- Chezy roughness coefficient [m/s2]. Required only for Voellmy rheology
**bfrict**=*float*- Angle of basal friction [deg]
**ifrict**=*float***[required]**- Angle of internal friction [deg]
**fluid**=*float***[required]**- Upward velocity of transition from solid to fluid of the landsliding mass [m/s]
**timesteps**=*integer***[required]**- Maximum number of time steps of the simulation [s]
**deltatime**=*integer*- Reporting time frequency [s]
**stop_thres**=*float*- Pearson value threshold for simulation stop [-]
**step_thres**=*integer*- Number of time steps for evaluating stop_thres value [-]
**threads**=*integer*- Number of threads for parallel computing
**h**=*string*- Prefix for flow thickness output raster maps
**h_max**=*string*- Prefix for maximum flow thickness output raster maps
**v**=*string*- Prefix for flow velocity output raster maps
**v_max**=*string*- Prefix for maximum flow velocity output raster maps

r.massmov is a numerical model that allows users to simulate the expansion (runout) and deposition of mass movements over a complex topography by approximating the heterogeneous sliding mass to a homogeneous one-phase fluid (following the approach proposed by Savage and Hutter (1989) and Iverson and Denlinger (2001)). The model describes the mass movements as a two-dimensional flux taking advantage of the shallow water equations. This formula is derived from the general Navier-Stokes equations under the hypothesis that the vertical components of velocity and pressure are negligible with respect to the horizontal components, and that the vertical pressure profile can be considered as almost hydrostatic (Kinnmark 1985).

The required inputs can be classified in three categories based on the information type:

- raster maps of the topography, in particular the sliding surface topography
*elev*(digital terrain model without the sliding body), the initial sliding mass thickness*h_ini*and the 'distance map'*fluiddist*, representing the cells distance from the collapsing body lower limit; - numerical parameters for the characterization of the mass material, density
*rho*[kg/m3], apparent yield stress*ystress*[Pa], Chezy roughness coefficient*chezy*[m/s2], dynamic viscosity*visco*[Pa*s], basal friction angle*bfrict*[deg], internal friction angle of the sliding mass during the expansion*ifrict*[deg] and the fluid rate*fluid*[m/s].This last parameter provides information on the transaction velocity of the sliding mass when passes from a solid state to a fluid state; together with the 'distance map' it allows to define the amount of mass mobilized as a function of time. It is worth noting that depending on the selected rheological law different sets of parameters are mandatory; - control parameters to stop the simulation (like maximum time step number
*timesteps*and/or automatic stopping criterion parameters*stop_thres*and*step_thres*) and to set the number of processors for parallel computing (*threads*). If the parallel computing is activated, and unless of different settings, the program runs using all the available processors.

The model outputs a series of flux velocity map (*v*) and deposit depth raster map (*h*) at different time step
according to the set deltatime parameter; additionally the module outputs two raster maps representing the
maximum thickness (*h_max*) and velocity (*v_max*) registered during the simulation.

The generation of the model input maps, in case the simulation refer to en existing collapse and pre and post event DTM is available, can be performed taking advantage of the GRASS modules; in particular:

- the sliding surface can be calculated by subtracting the collapsing body from the pre-event DTM (r.mapcalc)
- the collapsing body thickness can evaluated by considering the negative differences between the post and pre-event DTM multiplied for the cosine of the slope (r.mapcalc and r.slope.aspect)
- the distance map from the landslide toe can be obtained by applying the r.grow.distance module to the rasterized limits of the landslide

The module has been tested in several cases (see references), but up to now most of the simulations was done using a Voellmy rheology thus other rheology laws should be better investigated.

Begueria S, Van Asch T W J, Malet J P and Grondahl S 2009 A GIS based numerical model for simulating the kinematics of mud and debris flows over complex terrain. Nat Hazards Earth Syst Sci, 9, 1897-1909.

Iverson R M and Denlinger R P 2001 Flow of variably fluidized granular masses across threedimensional terrain: 1, Coulomb mixture theory. Journal of Geophysical Research 106:537-52

Kinnmark I P E 1985 The shallow water equations: Formulation, analysis and application. In Brebia C A and Orszag S A (eds) Lecture Notes in Engineering 15. Berlin, Springer-Verlag:1-187

Molinari M, Cannata M, Begueria S and Ambrosi C 2012 GIS-based Calibration of MassMov2D. Transactions in GIS, 2012, 16(2):215-231

Savage S B and Hutter K 1989 The motion of a finite mass of granular material down a rough incline. Journal of Fluid Mechanics 199:177-215

r.slope.aspect

r.mapcalc

*Original version of program:*

Santiago Begueria

*The current version of the program (ported to GRASS7.0)*:

Monia Molinari, Massimiliano Cannata, Santiago Begueria.

Available at: r.massmov source code (history)

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