Monday, February 27, 2017

Avachinsky Volcano

From the International Space Station  ISS 2 May 2011 Avachinsky
Oblique view from south of Avachinsky active (left) and inactive Kozelsky (right)

Saturday 25 February 2017 ski trail from Lesnaya to foothills of Avachinsky.  Tanya Pinegina skiing, JB photo.
Saturday we skied to the foothills of Avachinsky volcano (“Avacha”), the active stratovolcano just north of Petropavlovsk.  Indeed, much of the city of Petropavlovsk sits on an extensive volcanic debris flow from the cataclysmic eruption of old Avacha about 30,000 years ago.  Truck-sized rocks from this debris flow emerge from the local park near our Institute and lie along the ski trail.
2010 winter view toward north of Koryaksky (left) and Avachinsky (right) from our office window at the Institute of Volcanology and Seismology, Far East Division, Russian Academy of Sciences, Petropavlovsk-Kamchatsky (JB photo)

Avacha's nearest neighbor, to the east, is Kozelsky, which is part of the Avacha complex.  To the west looms Koryaksky volcano, which is much less active than Avacha in Holocene times (last ~12,000 years). Active volcanoes, if conical, tend to have smooth flanks, as does the young Avacha cone, whereas Koryaksky is deeply incised by erosion, as is Kozelsky.  In all my years visiting Kamchatka, I have had innumerable views of these volcanoes, though almost always from the south side.  18th century navigators identified their approach to the narrow opening of Avacha Bay by the “three volcanoes” they could see from afar. 1851 crest of Kamchatka, to the right:

I did find a picture (above) in my scanned collection of an aerial shot I took from the north in summer of 1996 (note there is a large cloud that is not a mountain!).  It is easier from the north side to see that the active cone of Avacha lies within the much larger, former edifice of old Avacha.  The one time I was on foot on the north side, I could see Avacha’s and Koryaksky’s more intensely glaciated northern flanks.  On our way toward the pass between the two, we made the mistake of getting too high too fast and ended up crossing active moraines and debris-covered glacier snouts.  Not fun. 

Avacha has a long record of historical eruptions:  (2001), 1991, 1945, 1938, 1926, 1909, 1901, 1894, 1881, 1878, 1855, 1854, 1853, 1851, 1828, 1827, 1779, 1772 and 1737.  [The largest historical eruptions are in bold italics, the next largest set in bold; data from Smithsonian Global Volcanism Program based on work by Kamchatka geoscientists (references there) In the Smithsonian catalogue, Avacha is volcano 300100.  This photo (left, by Oleg Volynets) is from the 1991 eruption.  

From these data, as well as from analysis of surrounding topography and of the prehistoric record, Institute geologists have prepared a volcanic hazard map for Petropavlovsk and the surrounding area (map above).  These hazards include lava flow, pyroclastic flow, debris avalanche, eruptive blast, debris flow, mudflow (lahar) and volcanic ash/cinder fall.  For most of these, being farther away and higher is safer, but ash falls are primarily directed by winds at the time of eruption, so their primary direction can be quite variable.  Link to the above map.  Legend for this map

The cinder and ash (tephra) deposits from historical eruptions have been used by Tanya Pinegina (tsunamis) and Lilia Bazanova (Avacha volcanic history) to help map out not only the tephra layers themselves, but also to use these layers to identify and map historical tsunami layers above and between them.  Their work has helped to determine which of Kamchatka’s historical earthquakes were the largest and most tsunamigenic. Such analysis is particularly important because the shorelines where the historical ash layers fell are also the ones closest to Kamchatka’s center of population (Petropavlovsk-Kamchatksiy on the map below).  I participated in some early phases of this work at Khalaktirka beach, where we could map out the tsunami deposit from the 1952 Kamchatka great earthquake because it lies almost directly above the 1945 Avacha ash layer.  To the right is a picture of Lilia (lower left) and Tanya (above) documenting some of the many Avachinsky tephra along a stream cut near Khalaktirka beach.        
Lilia Bazanova with her colleagues Olga Braitseva and others have also worked out a long prehistoric record of eruptions of Avachinsky volcano.  Given its historical record, it is not surprising that Avacha has generated volcanic debris deposits and/or mappable tephra layers every couple of centuries or so – the record is more difficult to tease out the farther back in time because the layers are obscured by plant roots, weathering and other soil processes.  Several of these layers record eruptions larger than any of the historical ones, including an eruption that sent ash as far as Ust’ Kamchatsk (see map below).  We use layers from these eruptions to work out the prehistory of tsunami deposits and their generating earthquakes.  That is “paleotsunami” analysis—I had to get the word paleotsunami in here because that’s in the name of my blog!

One could certainly get the impression from the pictures thus far posted here that Avachinsky is one big snow cone. However, I found this picture by Vera Ponomareva to show just how un-snowy it can be by end of summer. Vera constructed a website about Kamchatka volcanoes hosted by the Institute of Volcanology and Seismology.
Climbing Avachinsky:  I was with a group of tsunami scientists, visiting Petropavlovsk in the summer of 1996, who attempted to climb Avacha on a windy, rainy day.  We failed miserably, not least because many of us were not really prepared for such a climb, despite the valiant cheerleader guide we had, Elena Sassorova.  More about these women geoscientists at this blog post.  On a perfect day in the summer of 2000, finally I succeeded in summiting, guided by Sasha Storcheus.  The cindery cone was frozen as we ascended in the morning and soft when we descended. I don’t have digitized photos of that climb—I was surprised to see the lava pool at the top and to see fresh sulfur deposits.

Photo left:  2004 by JB.  Photo right: on Tolbachik by Pavel Isbekov. 

Tragically, on 3 March 2013, our dear friend and colleague Katya Kravchunovskaya was one of three mountaineers who died while trying to help a lost tourist in a snowstorm on Avacha.  We miss her terribly.

No comments:

Post a Comment