Rocks and Gases

Descriptions of volcanic deposits

The type of volcanic deposits is entirely dependent on the eruption style.  Karymsky volcano commonly has a Vulcanian or Vulcanian-Strombolian eruption style (VONA/KVERT).  As a result, Karymsky produces both pyroclastic and effusive deposits.  Volcanic deposits at Karymsky volcano include blocky lava flows, PDC deposits, fallout deposits (including blocks, bombs, and ash) (Global Volcanism Program).   

The volcanic deposits of Karymsky volcano are primarily confined to the caldera in which it is nested.  However, fall out often drifts 100’s of kilometers before it settles (Global Volcanism Program).      

Geochemistry and Petrology

During the Holocene, magma that Karymsky erupted ranged from basalts to rhyolites.  Basalt eruptions in the Karymsky volcanic center have been rare and small in volume (Izbekov et al., 2000).  According to Kamchatka Eruption Response Team (VONA/KVERT), the volcano primarily produces andesites, andesite-dacites, and dacites.      

The 1996 eruption was a rare event, where magma erupted from two neighboring vents simultaneously.  However, the compositions erupted were very different.  The Academy Nauk vent erupted basalt (52.2 wt% SiO₂) while the Karymsky volcano erupted andesite (62.4 wt% SiO₂).  Andesites from the 1996 Karymsky eruption were very similar to andesites produced in the past (Izbekov et al., 2000).         

The 1996 eruption was triggered by the injection of a basalt dike along the pre-existing fault where it intersected the shallow magma chamber beneath Karymsky.  The recharge of basalt into the andesitic magma chamber forced the pre-existing andesitic magma out (Izbekov et al., 2000).  A couple kilometers to the south, the basaltic dike intersected the surface beneath Karymsky Lake and caused phreatomagmatic eruptions inside Academy Nauk caldera (Izbekov et al., 2004).    

Total alkalis vs silica diagram for 1996 Karymsky andesites and Academy Nauk basalts.  The horizontal hatching represents andesites and the vertical hatching represents basalts since 5300 yr BP.  The circle symbols represent data collected by Izbekov and others (2004).  The volcanic products from Karymsky were much more silica-rich than the eruptive products from Academy Nauk (Diagram from Izbekov et al., 2004 p. 2334).

Karymsky produced porphyritic andesite with phenocrysts of plagioclase, clinopyroxene, orthopyroxene, and magnetite.  The lavas produced were vesicle-poor, while volcanic bombs were very vesicular (Izbekov et al., 2004)

Academy Nauk predominantly produced porphyric basalt.  The basalt contains minor silicic xenoliths with signs of assimilation (Izbekov et al., 2004).  Academy Nauk produced a large amount of basaltic bombs, which are very vesicular and phenocryst-rich with plagioclase, clinopyroxene, and olivine as major phase (Izbekov et al., 2004). 

Hydrothermal activity

Numerous geysers and hot springs are currently active along the fault between Karysmky and Academy Nauk caldera (Izbekov et al., 2004).