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Debris-flow generated tsunamis can be extremely dangerous for lakeside settlements and infrastructure. Debris-flow composition strongly affects debris-flow thickness and velocity, and therefore also the generated tsunami. This interaction is, however, poorly understood. We investigate the effects of debris-flow volume, composition (gravel, sand, clay, water) and subaerial outflow slope on wave celerity and amplitude in a small-scale physical model consisting of an inclined outflow channel which transits into a three-dimensional water reservoir. We find that upon debouching, a debris flow pushes the water forward until wave celerity exceeds subaqueous debris-flow velocity (i.e. Froude number <1). The wave then detaches from the debris flow and travels into the far-field. Pushing of the debris-flow oversteepens and accelerates the generated wave beyond the celerity predicted by linear wave theory for shallow waves. It also increases its non-linearity but does not result in wave breaking. Wave celerity has the strongest relation with debris-flow velocity. Debris-flow velocity increases with increasing water and clay content (up to 22%), which both lubricate the flow. Far-field leading wave amplitude has the strongest relation with debris-flow momentum (velocity times effective mass), which is mostly a function of debris-flow thickness, water and clay content. We test the applicability of published (semi-empirical) equations for predicting tsunami amplitude generated by dry landslides, and show that they are to some extent also applicable to debris flow. Potential scale effects, especially considering the smallest waves and water depths, could influence the applicability of these predictors and translation of the results to the field scale. Our results demonstrate the importance of debris-flow composition on tsunami generation and evolution, and thus the necessity of including flow composition in predictive simulation models.

© 2017 Pudasaini, Wilson, Ji, van Dorst, Snape, Palmer, Burns and Ferrari. Browning Peninsula is an ice-free polar desert situated in the Windmill Islands, Eastern Antarctica. The entire site is described as a barren landscape, comprised of frost boils with soils dominated by microbial life. In this study, we explored the microbial diversity and edaphic drivers of community structure across this site using traditional cultivation methods, a novel approach the soil substrate membrane system (SSMS), and culture-independent 454-tag pyrosequencing. The measured soil environmental and microphysical factors of chlorine, phosphate, aspect and elevation were found to be significant drivers of the bacterial community, while none of the soil parameters analyzed were significantly correlated to the fungal community. Overall, Browning Peninsula soil harbored a distinctive microbial community in comparison to other Antarctic soils comprised of a unique bacterial diversity and extremely limited fungal diversity. Tag pyrosequencing data revealed the bacterial community to be dominated by Actinobacteria (36%), followed by Chloroflexi (18%), Cyanobacteria (14%), and Proteobacteria (10%). For fungi, Ascomycota (97%) dominated the soil microbiome, followed by Basidiomycota. As expected the diversity recovered from culture-based techniques was lower than that detected using tag sequencing. However, in the SSMS enrichments, that mimic the natural conditions for cultivating oligophilic "k-selected" bacteria, a larger proportion of rare bacterial taxa (15%), such as Blastococcus, Devosia, Herbaspirillum, Propionibacterium and Methylocella and fungal (11%) taxa, such as Nigrospora, Exophiala, Hortaea, and Penidiella were recovered at the genus level. At phylum level, a comparison of OTU's showed that the SSMS shared 21% of Acidobacteria, 11% of Actinobacteria and 10% of Proteobacteria OTU's with soil. For fungi, the shared OTUs was 4% (Basidiomycota) and < 0.5% (Ascomycota). This was the f