Abstract—We discuss the water!level variations in the E!1 well for the time period between May 2006 and
2010, inclusive. A trend towards an increasing level at an abnormally high rate occurred from mid!2006 to
December 2009. This increase is regarded as the response of the aquifer of gas!saturated ground water that
exists in the volcanogenic–sedimentary deposits of the Avacha volcano!tectonic depression to volumetric
strain changes during the precursory period and the occurrence of a swarm of small earthquakes ( = 8.3)
in the area of Koryakskii Volcano and to its phreatic eruption. We estimated the volumetric compression as
Δε = –(4.1 × 10–6–1.5 × 10–5) from the amplitude of water!level rise using the elastic parameters of the wa!
ter!saturated rocks. While the strain source was active, we observed a decreasing sensitivity of the hydrologic
regime in the well to the precursory processes before large (M ≥ 5.0) tectonic earthquakes.

The article presents the first study of isotopic and geochemical composition of Late Cretaceous - Early Paleogene kitilgin high-potassium volcanic rocks from the Valaginsky Range, Kamchatka. Mineralogic and chemistry composition as well as radiogenic isotope ratios of rocks show that they are similar to kirganik shoshonites from the Sredinny Range, Kamchatka. Low HFSE composition respectively to MORB composition, low 87Sr/86Sr and high 143Nd/144Nd suggest that melts were formed from MORB-like mantle. Rocks enriched with LILE give evidence for fluid mantle admix caused by initial magma evolution.