| Abstract |
On June 3, 2007 catastrophic landslide took place in Geysers Valley, Kamchatka. It started with steam explosion and was then was transformed into debris mudflow. Within 2 minutes (D. Shpilenok, pers.com. 2007), 20 mln m3 of mud, debris, and blocks of rock were shifted away. As a result of this, eight major geysers located at lower elevations were sealed under 20-40 m of thick mud debris flow, and eleven geysers sank beneath the 20 m deep Podprudnoe Lake created by rock dam across the Geysernaya river. Analysis of the hydrogeological conditions of the landslide, which took place in the Geysers Valley shows that a possible cause of this was a long term steam upflow occurred along inclined bottom of the Geyzernaya pumice tuffs unit, which finally resulted in deep hydrothermal alteration of the pumice to highly silicified zeolites and montmorillonite and the corresponding loss of their stability. Landslide triggers may include plumbing magma system pressure increase, seasonal flooding, and steam explosions. Two years of monitoring the two key geysers’ cycling parameters (Velikan and Bolshoy), Podprudnoe Lake level and thermal discharge from the lake, yield to the following results: 1.Velikan maintained stable geyser activity cycling with an average time period slowly decreasing from 382 min (July 2007 – March 2008) to 372 min (April 2008 – July 2008), 347 min (August 2008 – October 2008), 345 min (November 2008 – March 2009), and almost returning to the time period recorded before the landslide - 339 min (2003). Some cycling period increase after landslide off-load may characterize geyser stress sensitivity. Velikan cycling is also very sensitive to the heavy rains and winter snowfalls, which may increase the idle period up to 32 hours. 2.Bolshoy showed cycling with average time period declining from 84 to 64 min between Sept 2007 and May 2008 when Podprudnoe Lake was at a low level, while the high level in the summer of 2008 pushed cold water inflows from Lake into the geyser channel and terminated its activity. 3.Thermal discharge of the Geysers Hydrothermal System catch at the exit from Podprudnoe Lake is sensitive to the Lake level, increasing to 300 kg/s in the winter time, and sharply declining to 30-100 kg/s during flood period in June. |