Tolbachik is a pair of volcanoes at the southern end of the Kliuchevskaya volcano group on the Kamchatka peninsula, Russia. They erupt primarily basalt and andesitic magmas. One of the pair, Plosky Tolbachik is a shield volcano topped with calderas up to 3 km in diameter. The other, Ostry Tolbachik is a stratovolcano that has evidence of at least one flank collapse.
Plosky Tolbachik was the location of two of the largest effusive basaltic eruptions over the last century, matched only by the output from Holuhraun in Iceland in 2014.
It is a relatively unpopulated area with only about 10,000 living within 100 km of the group.
KVERT is the government monitoring organization. Their home page is here: http://www.kscnet.ru/ivs/kvert/index_eng.php
The Tolbachik home page is here: http://www.kscnet.ru/ivs/kvert/volc.php?name=Plosky%20Tolbachik&lang=en
Tolbachik webcam is located here: http://geoportal.kscnet.ru/volcanoes/volc.php?ln=vid&name=Plosky%20Tolbachik
Kliuchevskaya Volcano Group
The Kliuchevskaya (sometimes spelled as Klyuchevskaya) Volcano Group is located almost directly above a triple junction as the Pacific Plate subducts below the North American and the Okhotsk Plates. Also being subducted are the Emperor Seamount Chain. This provides a prodigious magma supply.
The group includes Ushkovsky, Klyuchevskaya Sopka, Kamen, Bezymianny, Zimina, Udina and Tolbachik. South of the group is Kizimen. North of the group are a pair of dormant, flank collapse volcanoes just north of the village of Klyuchi and finally Shiveluch. The entire group is littered with flank collapses, lateral blasts, effusive eruptions and massive pyroclastic flows. It measures roughly 20 km by 40 km, with the long axis generally north – south. Kizimen is some 78 km to the south of the group. Shiveluch is some 80 km to the north of the group and marks the northern end of Kamchatka volcanic activity.
Here are some thumbnail sketches of the volcanoes listed above.
Shiveluch fills a 9 km diameter caldera breached to the south. It is one of Kamchatka’s largest and most active volcanoes. It is active with over 60 eruptions in the Holocene. A very dangerous mountain. https://volcanocafe.wordpress.com/2012/09/03/shiveluch-the-bad-boy-of-kamchatka/
Volcanoes north of Klyuchi show up on the map as a pair of craters out of same edifice. The horseshoe in the southern volcano points generally SE while the horseshoe amphitheater on the northern volcano points generally N. They appear to be unnamed at least on the maps I found. The cones are well eroded, indicating a significant period of inactive time.
Kizimen, south of the group is described as morphologically similar to Mount St. Helens before the 1980 eruption. It tops out at over 2,300 m. The volcano is relatively young thought to be around 12,000 years old. There is evidence of at least one lateral blast creating a 1 km crater breached to the NE. It is currently in dome-building with the occasional dome collapse. http://volcano.si.edu/volcano.cfm?vn=300230
In the group itself, Ushkovsky is the NW corner of the grouping. It consists of two massive stratovolcanoes. Ushkovsky (Plosky) is nearly 4,000 m high, topped with a 5 km diameter caldera. Adjacent is a complete stratovolcano, Krestovsky (Blizhny Plosky) which is some 4,100 m high. There are lines of cinder cones down the flanks and into the lowlands. The most recent eruption from Ushkovsky was 1890. Two massive eruptions have been confirmed some 6,670 and 7,550 years ago. http://volcano.si.edu/volcano.cfm?vn=300261
Klyuchevskaya Sopka is some 11 km to the east of Ushkovsky. It is another stratovolcano, this one over 4,800 m high. The volcano is thought to be some 6,000 years ago and has been in near continual eruption since its formation. The USGS reports that over 100 flank eruptions have taken place over the last 3,000 years. There are 71 observed eruptions since 1900 alone, so the previous number is likely to be low by a wide margin. This volcano has not yet had a caldera forming eruption. http://volcano.si.edu/volcano.cfm?vn=300260
Kamen is slightly to the south of Klyuchevskaya and forms the middle of a short chain of three volcanoes. It has not been recently active but did suffer a major flank collapse that sent 4 – 6 km3 of debris over 30 km to the SE. The remaining mountain tops out at just under 4,600 m. Activity at Kamen is thought to have begun in the late Pleistocene and continued into the Holocene. The GVP does not list any known eruptive activity. http://volcano.si.edu/volcano.cfm?vn=300251
Bezymianny is a young volcano that marks the end of this 9 km long chain. It was formed some 4,700 years ago over an ancestral dome complex and edifice built some 7,000 – 11,000 years ago. There were three periods of activity over the last 3,000 years. The most recent period that began in 1955 broke a 1,000 year period of quiet. The 1955 eruptive period climaxed with a Mount St. Helens style eruption that produced a horseshoe shaped crater and lateral blast. The crater has been mostly refilled with ongoing dome growth, intermittent explosive activity and pyroclastic flows. The 1955 eruption was classed as a VEI 5. http://volcano.si.edu/volcano.cfm?vn=300250
Zimina is a pair of eroded stratovolcanoes some 13 km south of Bezymianny. The larger volcano tops out at just under 3,100 m. Both are topped with icecaps. The southern peak produced a flank collapse debris avalanche the traveled over 10 km. This collapse does not appear to be connected to a lateral blast. There are no known historical eruptions from Zimina. http://volcano.si.edu/volcano.cfm?vn=300242
Another 12 km SSW from Zimina we find Udina volcano. This marks the southeastern end of the volcano group. Udina consists of two stratovolcanoes constructed along generally an E – W line. The western volcano is called Bolshaya Udina and is over 2,900 m high. It is generally andesitic and has a large lava dome on its SW flank. The eastern volcano, Malaya Udina is generally basaltic and tops out at over 1,900 m. It also has small domes on its flanks. There are no known historic eruptions from Udina. http://volcano.si.edu/volcano.cfm?vn=300241
One thing to note about the group, is that the magmas tend to change from andesitic to basaltic as we work our way south from Shiveluch. The two southernmost volcanoes Udina and Tolbachik have significant basaltic components.
The final volcano in the group is Tolbachik. It is some 15 km NNW from Udina. Like Zimina and Udina, it also consists of a pair of cones. The shared edifice supports two different volcanoes. Ostry Tolbachik is a stratovolcano topping out at some 3,600 m. The second volcano is a basaltic shield called Plosky Tolbachik. It is topped with nested Hawaiian-style calderas (likely subsidence) measuring up to 3 km in diameter. Ostry Tolbachik had a flank collapse generally south some 6,500 years ago. The flank collapse took place about the same time as a major effusion eruption from Plosky Tolbachik. There are rift zones that have eruptive large quantities of basalt, with the 1975 – 1976 eruption being the largest historical basalt eruption in Kamchatka. A similar eruption took place from 2012 – 2013. http://volcano.si.edu/volcano.cfm?vn=300240
The 2012 – 2013 was classed as a VEI 4 eruption due to the quantity of basalt erupted. It was an effusive eruption that started with Strombolian activity and climaxed in November 2012. During the initial phase, there was strong explosive activity that put a plume some 10 km high. Ashfall up to 4 cm was measured some 65 km away. After a few days, the eruption settled down to a more effusive nature, with lava eventually flowing some 10 km from the volcano. Total volume erupted was some 0.55 km3. https://volcanocafe.wordpress.com/2013/06/01/tolbachik/
The 1975 – 1976 eruption similarly combined an explosive start with an effusive end. In the end, it produced just under 1.2 km3 of basalt. It also produced around 0.7 km3 of tephras. Eruptive plume was measured over 13 km high. Basaltic lavas covered over 40 km2 of area. The eruption also created four new monogenetic cinder cones along the open rift. http://volcano.oregonstate.edu/tolbachik
There are numerous eruptions in the 20th century most of them in the VEI 2 – 3 range. Historic eruptions do not appear to be much larger than VEI 4.
This is a prodigious volcano that has produced significant basalt lavas over the last ten thousand years.
As mentioned previously, Tolbachik and the larger Kliuchevskaya Volcano Group sit very close to a triple plate subduction junction. Tectonics of Kamchatka were covered on a previous post on VH. For additional reading, the link takes you to the article. https://volcanohotspot.wordpress.com/2015/03/18/tectonics-of-the-kamchatka-peninsula/
The subduction provides a prodigious supply of magma for surface activity. In the case of this group, the magmas appear to be well mixed, though the composition changes regionally from andesitic to basaltic as you move south across the group.
Magma for Tolbachik appears to be supplied from a reservoir some 20 km below the volcano. It is held briefly and mixed in a region some 5 km below the eruptive rifts. The 1975 eruption had a third reservoir just below the surface that was filled when portions of the caldera at the top of the volcano collapsed a bit. The shallow chambers appear to be transient while the 5 km chamber appears to be long lived.
Magma for the 2012 eruption appears to come exclusively from around 5 km deep.
Interestingly, Tolbachik erupts two different types of basalts – high aluminum and high magnesium basalts. The chambers are hot, well mixed and regularly resupplied from new magmas below.
The old Volcano Café had a post that argued that volcanic activity in Kamchatka was driven by flat plate subduction. I believe this to be a bridge too far, as flat plate subduction, particularly the rollback when it starts moving back down into the mantle is more often than not tied directly to massive caldera formation, something we have yet to see in this portion of Kamchatka. The volume of dehydrating Pacific Plate debris and the Emperor Seamount chain being subducted appears to be quite enough to provide both the magmas and volatiles dissolved in them erupted and mixing below the surface. https://volcanocafe.wordpress.com/2013/06/03/central-kamchatka-depression/
This area is quite young and quite active. The volcanoes grow quickly and collapse just as quickly, more times than not without benefit of a lateral blast eruption. There are several amphitheaters from lateral blast eruptions. There are even summit calderas like we have seen in other subduction driven front arc volcanoes. Given the significant amount of melt powering four continuously erupting volcanoes, I believe this will continue to be one of the more dangerous active volcanic regions on the planet.