This study integrates some observational data and tests two models which may explain changes in the cycling mode of a couple of prominent geysers Velikan and Bolshoy, which has been recently interrupted by 3.06.2007 (20 mln m3) and 3.01.2014 (3.2 mln m3) catastrophic landslides-mudflows, coming from different directions. According to the observations of geyser Bolshoy, its average eruption period has decreased almost twofold and was 63 min after 3.06.2007 landslide, while its activity was defined by the level of Podprudnoye Lake. 3.01.2014 landslide released geyser Bolshoy from lake level dependency, since it dropped water level to 3.5 m and filled the lake with mudstones debris. Hence geyser Bolshoy adjusted its cycling to average time period of 30-45 min in 2014. Geyser Velikan observations expose essential decrease of eruption period from its average annual value of 379 min (2007) to 335 min in the first three years following the disastrous 3.06.2007 landslide, whereupon its average annual value was stabilized until 3.01.2014. It has been found out that geyser Velikan hydrogeological cycle shows eruption period increase in winter (on the average 41-45 min). 3.01.2004 landslide significantly hit geyser Velikan, and its average time period of cycling cut to 89-132 min in 2014. TOUGH2-models were used to understand the mechanisms of geysers sensitivity to surface boundaries condition changes: 1. Large scale Podprudnoe Lake injection model (this model describes a suddenly entranced Podprudnoe lake infiltration area on 3.06.2007); 2. Local geyser Velikan model (this model focused on the sensitivity of geyser Velikan to host local reservoir parameters).

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