Morphology-based characterization of intermediate to silicic lava flows: Application to the Central Andean Volcanic Zone

The morphology of a lava flow records the eruptive dynamics that governed its emplacement, evolution, and the rheological properties of the erupted magma. Although the dynamics and morphological classification of mafic lava flows have been widely addressed, the characterization of the morphological features of intermediate to silicic lavas is still not exhaustive. In this study, we perform a morphological-based characterization of lava flows based on DEM-derived data and satellite images. We analyzed a dataset of 49 intermediate to silicic lava flows from the Central Andean Volcanic Zone and quantified the maximum wavelength of their surface ridges, described as folds, and their relationship with thickness distribution, pre-surface slope, composition, and rheology. Furthermore, we introduced a Fourier analysis to quantitatively characterize the lava flows' plain-view shape and a novel method based on an S-Transform spectral analysis of grayscale satellite images to assess the surface folding pattern. We distinguish 4 main types of lava flows in the andesite to dacite compositional range. Ridged lavas have highly arcuate ridges with convex surfaces, large thickness, and a curved, smooth frontal lobe. Coulee lavas have intermediate characteristics between lava flows and domes, with relatively simple shapes, lengths that do not significantly exceed their width, vents generally located in the central zone of the flow, prominent ridges and crumble breccias. Leveed lavas, which include a wide range of flow lengths, have the simplest shapes, exhibiting marked channelization and a unique frontal toe of maximum thickness. Breakout lavas have the most complex plain-view shapes, with lateral and frontal lobes, poorly developed levees, and wider and thicker fronts. Transitional lavas, with intermediate characteristics in terms of folding patterns and shapes, are also recognized. We show that the maximum wavelength of surface deformation is not continuous along the flow surface and spatially correlates with thickness distribution. In addition, the maximum wavelength is poorly correlated with SiO2 content and weakly correlated with lava viscosity, showing a positive correlation with the gravitational component of the shear stress applied to the flow. Results suggest that the pre-eruptive slope and viscosity, along with the effusion rate, play a primary role in governing the general dynamics of the flow and thus the resulting lava morphology, impacting different measurable features such as length, width, branching, and general deformation dynamics of the flow. The recognition of the main characteristics of the different lava types and their controlling factors represents a first step for interpreting lava flow morphology in terms of the eruption characteristics. This strategy can be adopted to analyze and interpret terrestrial and extra-terrestrial lava flows remotely.