PRODUCTS OF THE 1907 ERUPTION OF SHTYUBEL VOLCANO, KSUDACH-CALDERA, KAMCHATKA, RUSSIA

On March 28, 1907, a sequence of explosive eruptions within the Ksudac h Caldera Complex, located in the southern part of the Kamchatka Penin sula, Russia, partially destroyed Shtyubel' Volcano, leaving a tuff co ne with a 1.5 km in diameter horseshoe-shaped crater filled with a dee p lake. The total estimated volume of erupted products is 2.4 km(3), o f which 1.9 km(3) consists of juvenile andesitic to rhyolitic material . The eruption can be subdivided into four phases. The first phase ope ned the vent and dispersed about 0.02 km(3) of pyroclastic fallout wit hin Ksudach Caldera. The second phase produced a Plinian column that d istributed about 1.5 km(3) juvenile pyroclastic fallout to north-north east and southeast. The third phase was characterized by a powerful bl ast explosion toward the north-northeast in a 60 degrees sector. The b last cloud traveled at least 100-110 ms(-1) to surmount topographic ba rriers 500-600 m high. Other explosions produced pyroclastic flows, su rges, and breccias that cover about 115 km(2) with a volume of 0.15 km (3). The fourth phase consisted of a series of shallow hydromagmatic e ruptions that emplaced five pyroclastic surge deposits with ash cloud surge beds at their tops to the west-northwest. Two or three of these surge clouds must have exceeded velocities of 100 ms(-1) in order to s urmount Ksudach Caldera walls. These deposits cover an area of 160 km( 2) with a volume of 0.2 km(3), Analyses of deposit structures, particl e textures, and fragment components indicate that the first two phases were magmatically driven. However, the last two phases were increasin gly hydromagmatic. Lack of erosional contacts between the deposits, ab undant impact sags at horizon tops, and absence of reworked materials within the sequence suggest that the eruption lasted only a few hours to a few days, Juvenile products range from basaltic andesite to rhyol ite in composition, Based on the variation of chemistry and texture of juvenile components, we hypothesize that there was a zoned magma cham ber below Shtyubel' Volcano just prior to the 1907 event.