Research Article Modeling of Landslide-Generated Tsunamis with GRASS Massimiliano Cannata IST-DACD-SUPSI, Institute of Earth Sciences University of Applied Sciences and Arts of Southern Switzerland Roberto Marzocchi IST-DACD-SUPSI, Institute of Earth Sciences University of Applied Sciences and Arts of Southern Switzerland Monia Elisa Molinari IST-DACD-SUPSI, Institute of Earth Sciences University of Applied Sciences and Arts of Southern Switzerland Abstract The following research aims to enhance and spread the capacity of assessing risk due to landslide-generated tsunamis by fostering the use of a GIS (Geographic Informa- tion System), and in this particular instance, an Open Source GIS (where “Open Source” can be loosely defined as freely available source code). For this purpose, we tested a procedure to be spatially implemented in the Open Source GRASS GIS through developing a module named r.impact.tsunami that simulates landslide- generated tsunami. In this article we present its application in a case study performed on Como Lake (Lago di Como) in northern Italy. The review of the results identified sources of uncertainties while the model sensitivity outlined the influence of the parameters governing the model. Moreover, in order to verify the model validity, we implemented a new module (r.swe), that simulates the tsunami propagation and run-up with the shallow water equations, and compared the results. Notwithstand- ing non-negligible differences, the two models produced results of the same magni- tude; this confirmed the validity of both models, although a rigorous validation of the models could not be performed due to the lack of observed data. Address for correspondence: Massimiliano Cannata, IST-SUPSI, Campus Trevano, CH-6952 Canobbio, Switzerland. E-mail: massimiliano.cannata@supsi.ch Transactions in GIS, 2012, 16(2): 191–214 © 2012 Blackwell Publishing Ltd doi: 10.1111/j.1467-9671.2012.01315.x