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, 43 (7), 1373-1389

How Well Can We Simulate Complex Hydro-Geomorphic Process Chains? The 2012 Multi-Lake Outburst Flood in the Santa Cruz Valley (Cordillera Blanca, Perú)

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How Well Can We Simulate Complex Hydro-Geomorphic Process Chains? The 2012 Multi-Lake Outburst Flood in the Santa Cruz Valley (Cordillera Blanca, Perú)

Martin Mergili et al. Earth Surf Process Landf.

Abstract

Changing high-mountain environments are characterized by destabilizing ice, rock or debris slopes connected to evolving glacial lakes. Such configurations may lead to potentially devastating sequences of mass movements (process chains or cascades). Computer simulations are supposed to assist in anticipating the possible consequences of such phenomena in order to reduce the losses. The present study explores the potential of the novel computational tool r.avaflow for simulating complex process chains. r.avaflow employs an enhanced version of the Pudasaini (2012) general two-phase mass flow model, allowing consideration of the interactions between solid and fluid components of the flow. We back-calculate an event that occurred in 2012 when a landslide from a moraine slope triggered a multi-lake outburst flood in the Artizón and Santa Cruz valleys, Cordillera Blanca, Peru, involving four lakes and a substantial amount of entrained debris along the path. The documented and reconstructed flow patterns are reproduced in a largely satisfactory way in the sense of empirical adequacy. However, small variations in the uncertain parameters can fundamentally influence the behaviour of the process chain through threshold effects and positive feedbacks. Forward simulations of possible future cascading events will rely on more comprehensive case and parameter studies, but particularly on the development of appropriate strategies for decision-making based on uncertain simulation results. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Keywords: GLOF; high‐mountain lakes; process chain; r.avaflow; two‐phase mass flow model.

Figures

Figure 1
Figure 1
Study area before and after the event under investigation. (a) General location; (b) Santa Cruz asnd Artizón valleys before the 2012 event; (c) Santa Cruz and Artizón valleys after the 2012 event; (d) upper part of the Artizón valley before the 2012 event; (e) upper part of the Artizón valley after the 2012 event. [Colour figure can be viewed at http://wileyonlinelibrary.com]
Figure 2
Figure 2
Deglaciation of the Artizón valley between 1948 and 1970 and formation of the lakes Artizón Alto and Artizón Bajo. Source: Servicio Aerofotogramétrico Nacional. [Colour figure can be viewed at http://wileyonlinelibrary.com]
Figure 3
Figure 3
The multi‐lake outburst flood of 8 February 2012. (a) Steep moraine slopes surrounding Lake Artizón Alto with the 2012 landslide; (b) bedrock step between the lakes Artizón Alto sand Artizón Bajo, impounding lake Artizón Alto; (c) failed dam of Lake Artizón Bajo; (d) middle part of the Artizón valley leading into an outwash plain; (e) outwash plain; (f) confluence of Artizón and Santa Cruz streams; (g) Santa Cruz valley floor covered by fine‐grained deposits; (h) damaged outlet of Lake Jatuncocha. Photos: Adam Emmer, 7 and 8 July 2015. [Colour figure can be viewed at http://wileyonlinelibrary.com]
Figure 4
Figure 4
Longitudinal profile through the Artizón and Santa Cruz valleys with the dominant processes and the locations of the cross‐profiles between Lake Artizón Alto and Lake Ichiccocha. [Colour figure can be viewed at http://wileyonlinelibrary.com]
Figure 5
Figure 5
Logical framework of r.avaflow. Only those elements relevant for the present study are shown. See Mergili et al. (2017) for a comprehensive logical framework. [Colour figure can be viewed at http://wileyonlinelibrary.com]
Figure 6
Figure 6
Spatial input and reference data for simulation of the 2012 Santa Cruz process chain with r.avaflow. The bold black lines separate the zones I–III. All raster maps are produced at a cell size of 5 m. [Colour figure can be viewed at http://wileyonlinelibrary.com]
Figure 7
Figure 7
Flow height maps derived in the computational experiment E1 for selected points in time, and for the maximum over the entire simulation (H Max). The dashed yellow line represents the main flow path (defined manually from the DTM and satellite imagery), the solid red line the observed impact area of the process chain down to Lake Jatuncocha. O1–O4 represent the output hydrographs (Figure 6 and Figure 8). [Colour figure can be viewed at http://wileyonlinelibrary.com]
Figure 8
Figure 8
Output hydrographs O1–O4 generated in experiment E1 (see Figure 6 for the location of the hydrograph profiles). Columns represent the discharge, lines the flow height. The solid component is shown above, the fluid component below the horizontal line. Note that the fluid components are drawn in negative direction in order to enhance the readability of the figure. (a) Output hydrograph O1; (b) output hydrograph O2; (c) output hydrograph O3; (d) output hydrograph O4. [Colour figure can be viewed at http://wileyonlinelibrary.com]
Figure 9
Figure 9
Flow height maps resulting from experiment E2 for selected points in time from t = 0 s to t = 100 s, representing the initial stage of the process chain. The dashed line represents the main flow path. (a) Simulation with 10 m cell size; (b) simulation with 5 m cell size. [Colour figure can be viewed at http://wileyonlinelibrary.com]
Figure 10
Figure 10
Simulated impact area (HMax ≥ 0.2 m) derived with six combinations of VR and δI (experiment E3). The observed impact area is shown as reference. [Colour figure can be viewed at http://wileyonlinelibrary.com]
Figure 11
Figure 11
Dependency of overtopping of the lakes Artizón Alto and Artizón Bajo on the combination of the release volume of the initial landslide V R and the basal friction angle δ I applied to r.avaflow. [Colour figure can be viewed at http://wileyonlinelibrary.com]
Figure 12
Figure 12
Simulated impact area (HMax ≥ 0.2 m) derived with three assumptions of δII (experiment E4). The observed impact area is shown as reference. [Colour figure can be viewed at http://wileyonlinelibrary.com]
Figure 13
Figure 13
Simulated impact area (H Max ≥ 0.2 m) derived with three assumptions of δ III (experiment E5). The observed impact area is shown as reference. [Colour figure can be viewed at http://wileyonlinelibrary.com]
Figure 14
Figure 14
Reconstructed and simulated entrained heights in the potential entrainment area (Figure 6). (a) Reconstructed entrained height (E Rec); (b) simulated entrained height (E Sim). [Colour figure can be viewed at http://wileyonlinelibrary.com]

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