Topography of the caldera of Bolshoi Semiachik , and his numerous volcanoes and domes
Both ends , north and south of the Kronotsky Reserve, are little illustrated.
Located south of the Kronotsky Reserve, the Bolshoi Semiachik Volcanic complex has been built in a large caldera 10 km wide , closed west side, and occupying a volcano- tectonic depression, dated from the late Pleistocene, along the Pacific coast Kamchatka .
The post- caldera volcanism includes lava domes , including Ivanov, the Ezh and Korona , and many stratovolcanoes , certain assets of the Holocene : the volcanoes Zubchatka ( Bolshoi Semiachik ) Zapadny Barany , Vostochny Barany , Zentralny Semiachik , Popkov , Plosky and Burlyashchy are the most important of the complex.
The Bolshoi Semiachik complex view of the wall of the caldera - The Zubchatka is the big building in the background - photo Nikolai Smelov / KSCNET
The dating of the dome Ivanov was not easy to establish. He did not produce lava flows and is not covered by layer of ash ... however we found a well near the dome, which was identified in, a layer of pumice lapilli andesitic , caught between the tephra of Karymsky - dated 5900 BC - and a layer of ash called "Lower yellow ash" - dated 7500 BC. This allows us to date the dome Ivanov between 6500 and 7000 BC .
Domes Ezh ( Hedgehog ) and Korona (Crown) were produced long lava flows and associated lahars , which allows them dating : to 3600 BC , according to a tehra,marker of the eruption of Avachinsky .
Bolshoi Semiachik - Ezh dome - photo Nikolai Smelov / KSCNET
The complex has a hydrothermal activity , especially located on the western slopes of the Bolshoi Semiachik and Zentralny Semiachik .
The eastern part of the thermal field Burlyashchy include steam jets , with temperatures up to over 137 ° C. The thermal field of the central Semiachik home the Chernoe lake, a lake emitting vapors.
Bolshoi Semiachik thermal field - left, thermal field Burlyashchy - right on Lake Chernoe - photos KSCNET - A click to enlarge .
North of Kronotsky Reserve, the Gamchen Volcanic Group forms a volcanic chain oriented North - South , with the massive Gamchen and the cone Barany , the Komarov , and the Vysoky .
Volcanic Group Gamchen : From left to right: the four summits of the volcano Gamchen , the yellowish summit of Komarov , composed of hydrothermally altered rocks , and to the extreme right, Vysoky volcano. - Photo Philip Kyle / KSCNET
The massive of Gamchen is a complex of four stratovolcanoes, surmounting a shield. The Severny Gamchen and Yuzhny Gamchen are two eroded Pleistocene stratovolcano . The Molodoi is a small stratovolcano located on the eastern flank of Severny Gamchen . The Barany is located on the south-eastern flank of Yuzhny Gamchen ; wearing a crater of youthful appearance , 500 m.on 200 , its eruptions , dated 1650 and 550 BC , produced a lava field extending NE and E . A young lava dome , the Lukovitsa , formed on the sidewall of Barany , at the end of the period of activity .
Collapses of the complex at the beginning of the Holocene and deposits of debris avalanches formed a field with an hummock topography on the east side of the volcano, called "Moon hills" .
In the foreground, the Komarov , followed by summits Gamchen - and at the bottom , right, the silhouette of Kronotsky - KSCNET / Photo Philippe Bourseiller / GVP
The uppermost zone of Komarov , hydrothermally altered - photo Philippe Bourseiller / KSCNET / GVP
The Komarov complex (or Komarova ) is surmounted by an eccentric caldera 4 km on 2.5 . The Vysoky and the Komarov has the same magmatic system, producing an andesite of same composition , and different from that of the volcano Gamchen .
The young cone Komarov , 2070 m high , was built at the western end of the caldera ; he wears two craters , one on top and one on the upper East side . All the summit region is subjected to extensive hydrothermal alteration , and retains active fumarole , as found on the side N and S.
The Vysoky further north , has been active since the early Holocene until the beginning of our era , while the Komarov began to form there 1500 years. , after stopping activity of Vysoky . Bizarrely , the Vysoky is not included on any list of active volcano.
The Vysoky was active until the beginning of our era , with the lava flow dated 2000 years ago - photo Vera Ponomareva / KSCNET
- KSCNET - Kamchatka Holocene Volcanoes - link
- Global Volcanism Program - Komarov
- Global Volcanism Program - Gamchen
- Global Volcanism Program - Bolshoi Semiachik