Tolbachik is a basaltic volcanic complex, located at the southern end of the Kliuchevskoi volcanic group in the Kamchatka Peninsula, Russia. The complex is made up of Ostry Tolbachik (3,682m); Plosky Tolbachik (3,085m) and the Tolbachik Lava Field. Ostry Tolbachik (3,682 m) is an extinct stratovolcano. Plosky Tolbachik is shield volcano with nested Holocene Hawaiian-type calderas up to 3 km in diameter; its summit caldera was formed with major lava effusion about 6,500 BP ago, and about the same time as a large southward-directed sector collapse of Ostry Tolbachik.
Tolbachik is composed of medium – K basaltic andesite. The slag deposits of Tolbachik are rich in minerals. 39 were first described from here, including Alarsite and Tolbachite. Tolbachik’s lavas originate from modification of H2O rich eclogitic melts by interaction with mantle wedge or through melt fluxed mantle melting. Mineral content of the lavas (Mg and Ni) suggest that the primary melts are derived from a mantle wedge. The major elements of Tolbachik’s basalts are similar to primitive MORB.
Volcanic activity in Kamchatka has been dated back to the Cretaceous. Plateau basalts were erupted between the Pliocene and the Lower Pleistocene. Activity then increased during the Upper Pleistocene to the Holocene.
The current plate tectonic configuration originated during the Late Miocene to Early Pliocene. The Kamchatka arc is located at the NE of the convergent boundary where the Pacific Plate subducts below the Okhotsk Plate. At the northern end of the volcanic arc, there is the Aleutian-Kamchatkan triple junction, where the plate boundary changes from convergent to strike slip. To further complicate matters, the Emperor Seamount Chain is also being subducted under Kamchatka.
Quaternary volcanic activity is in three zones parallel to the Kuril–Kamchatka Trench: the Eastern Volcanic Front; the Central Kamchatkan Depression and the Western Volcanic Zone. Tolbachik is located in the Central Kamchatkan Depression.
Tolbachik in the Holocene
A regional fissure zone started to form at the start of the Holocene. The zone crossed Plosky Tolbachik volcano, filling it with new high-K magma. It also produced the Tolbachik lava field. A 3-km summit caldera formed following a series of flank eruptions. The caldera was partly filled later by a shield-like volcano. A smaller caldera and a modern crater, intermittently filled by a lava lake, are located in the western part of the larger caldera. Plosky Tolbachik has produced small ash eruptions in Historical times.
The lava field produces two different series of lavas: high-K high-Al basalts and medium-K high-Mg basalts. Low-viscosity high-K basalts have been erupted during the whole Holocene, while medium-K high-Mg lavas are more recent – first appearing approximately 1,700 BP. Some mixed lava varieties have also occurred.
The Great Tolbachik Fissure eruption in 1975-76
The 1975-76 eruption was the largest historical basaltic eruption in Kamchatka (VEI-4). The lavas were: basalt, picro-basalt, andesite and basaltic-andesite. The eruption vents were located along a 28-km-long fissure, producing both medium-K high-Mg and high-K high-Al basalts. Three large cones and a number of lava flows were formed; and, approximately 0.7 km3 of airborne tephra were produced. Most of the erupted products were medium-K high-Mg basalt. Towards the end of the eruption, the lava composition changed to high-K high-Al basalts with some transitional varieties. Total volume of the erupted products is estimated at around 1.18 km3
2012 – 13 Eruption
The 2012 – 13 (still in progress at the time of writing) eruption is similar to the 1975-76 eruption. An explosive eruption began on 27th November 2012. Ash rose to a height of 33,000 ft. A 4-5 km fissure occurred at Tolbachinsky Dol. A 6-7 km fissure occurred at Plosky Tolbachik. Activity is Strombolian at several vents.
The earthquakes occurring under Tolbachik show the following patterns (this excludes the deeper EQs occurring from the subducting Pacific Plate):
GeoLurking estimates that the total SO2 release from this eruption is around 63,179,566 to 73,709,494 metric tonnes, based on geochemistry found in “Sourced and Fluids in the Mantle Wedge below Kamchatka, Evidence from Across-arc Geochemical Variation” Churikova et al (2001) for Tolbachik, and formulas from “Volcanic Degassing” article: “Sulfur release from flood lava eruptions in the Veidivotn, Grimsvotn and Katla volcanic systems, Iceland” Thordarson et al. Pinatubo produced around 20,000,000 metric tonnes.
John Search: http://www.volcanolive.com/tolbachik.html
Institute of Volcanology and Seismology, Kamchatka, Russia: http://www.kscnet.ru/ivs/volcanoes/holocene/main/textpage/tolbachik.html
“Geochemistry of Primitive Lavas of the Central Kamchatka Depression: Magma Generation at theEdge of the Pacific Plate”, Maxim Portnyagin, Ilya Bindeman, Kaj Hoernle and Folkmar Hauff
“Sources and Fluids in the Mantle Wedge Below Kamchatka, Evidence from Across – arc Geochemical Variation”, T Churikova, F Dorendorf and G Worner, Journal of Petrology, Volume 42, Number 8, Pages 1567 – 1593, 2001.