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Earth of fire

Actualité volcanique, Articles de fond sur étude de volcan, tectonique, récits et photos de voyage

Publié par Bernard Duyck
Publié dans : #Excursions et voyages
 Topography of the caldera of Bolshoi Semiachik , and his numerous volcanoes and domes

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 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

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 .Bolshoi Semiachik thermal field - left,  thermal field Burlyashchy - right on Lake Chernoe - photos KSCNET -  A click to enlarge .

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

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

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 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

The Vysoky was active until the beginning of our era , with the lava flow dated 2000 years ago - photo Vera Ponomareva / KSCNET

Sources:

- KSCNET - Kamchatka Holocene Volcanoes - link

- Global Volcanism Program -  Komarov

- Global Volcanism Program - Gamchen

- Global Volcanism Program - Bolshoi Semiachik

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