Mobility, Runout and Inundation Zone Analyses of Hazardous Gravity-Driven Volcanic Phenomena: Preliminary Results from Turrialba Volcano, Costa Rica

Large volcanic landslides are amongst the most devastating natural phenomena and can affect large areas on a local to regional scale. Moreover, there is evidence of these events on most mature stratovolcanoes, highlighting the relatively high frequency of occurrence. Once a flank or sector collapse is initiated, the flow behaviour of such events, which have been extensively studied, shows that volcano collapses can generate not only rock avalanches with restricted runouts, but also mobile debris flows and lahars that enlarge by bulking as they flow. Thus, the volumes, mobility and hence inundation areas of collapse-generated runout flows can increase greatly beyond their sources.

Turrilaba volcano in Costa Rica is a large stratovolcano which remains largely unstudied. However, recently, the need for a risk assessment is highlighted by an exponential increase in seismic and fumarolic activity in the last five years. The main drainage systems of Turrialba have the potential to channelize flows towards the populated cities of Turrialba (15 km to the south) and Guapiles and Siquirres (25 km to the north).

Herein a preliminary hazard assessment is carried out studying the potential of flank and sector collapses on Turrialba and the runout distances of the deposits. This is achieved by a combined approach of analytical and numerical models used to study the nature and volume of the initial collapse. Runout distances and inundation areas of the deposit are studied using a simple Montecarlo flow-routing model and a finite volume code on a geographical information system with different low-quality available digital terrain models: (1) derived from 1:50 000 cartography and (2) SRTM 30 arc-second data.

In order to provide a more complete first draft of a hazard map of Turrilaba, preliminary analyses of additional volcanic gravity-driven hazardous phenomena such as lahars and small pyroclastic flows are also performed.