Shiveluch – the Bad Boy of Kamchatka: Part Two

With the Baidarny lava ridge and caldera rim in the foreground, Shiveluch broods in 1994. The smoking cone sits in a crater that was believed to have been formed in the major collapse event of 600 years ago. (Alexander Belousov)

For nearly a century after the 1854 eruption Shiveluch had been highly active, building cones that had eventually filled the ‘crater within a crater’ that had most likely been formed in the last major collapse event of 600 BP. But then, in 1950, activity came to a halt apart from steaming. For over a decade there were no explosions, no eruptions, no extrusions.

“I’ve just been ‘away’ for a while … or  ”The ‘Big One’ of 1964

One might have been lulled into some sense of security by this lack of explosive action, but such is Shiveluch’s character that it can never be ignored. The first inkling of renewed activity came on 24 January 1964, when an earthquake was recorded under the mountain. Seismic activity ebbed and flowed as the year progressed, but during October intense activity set in.

At around midnight on the night of 11/12 November the quakes increased in severity and frequency to the point where they became individually unreadable on the seismographs. Some were felt up to 80 km away in Kliuchi. These quakes were entirely magmatic in nature, and reached M6 in strength as magma pushed upwards. Degassing from the magma as it rose almost certainly increased pore-fluid pressure within the edifice itself, further adding to the stress in the system.

With Shiveluch still gripped by the dark of the Kamchatkan winter night, the strongest quake yet hit the mountain at 07:07, and the eruption started. It kicked off in spectacular fashion with over a cubic kilometre of structural edifice collapsing and forming a massive debris avalanche that tumbled down the mountain, picking up speed as it glided over a lower layer of churning, bouncing fragments.

A phreatic explosion followed almost immediately, releasing a large, gypsum-rich ash cloud. After 13 minutes, with the magma’s route to the surface having been cleared to an extent by the landslide and explosion, Plinian activity began with juvenile tephra being ejected. From 07:47 pumiceous pyroclastic flows were formed. Volcanic tremor and air wave energy (recorded by barometer) increased at this time, peaking at around 08:10, and then subsided swiftly a few minutes later. The eruption ended at 08:22.

In little over an hour it had all but swept away Suelich and the other post-1854 lava domes, as well as the hill known as Arbuzik, which was probably a ‘toreva’-type slide-block from the 600 BP collapse. Shiveluch had thus essentially returned to close to its 600 BP topography, at least at the top of the mountain. Lower down, the leading elements of the debris avalanche spread rubble deposits out to 16 km distance. The avalanche covered an area of 98 km⌃2, with an average depth of 3 to 15 metres, although in places depressions were filled with deposits up to 150 metres deep. The final elements of the structure to fall resulted in large, backwards-rotating ‘toreva’ blocks sliding down the slope to come to rest across the breached crater, forming giant ‘steps’ that are visible today. The eruption also produced an estimated 0.8 km⌃3 of juvenile material through the initial Plinian phase and the more productive pyroclastic flow phase.

Before and after photos show the enormous scale of the 1964 collapse. Note that the entire central dome complex is gone, redistributed across a wide area at Shiveluch’s base. (Yuri Doubik, IVS Petropavlovsk via GVP website)

In the initial analysis of the eruption a ‘directed blast’ element was suspected, as had happened at Bezymianny in 1956 and Mount St Helens in 1980. However, subsequent research by Belousov and colleagues showed that this had not been the case. A lack of directed blast was attributed to the fact that the volcano had failed structurally before potentially explosive magma had risen into the edifice itself, unlike in the other two volcanoes where magma-filled cryptodomes had formed and had become visually obvious in the days prior to the eruptions. No such deformation was noted at Shiveluch.

In the case of Bezymianny and Mount St Helens it was the ‘over-steeping’ of the cryptodomes that had most likely initiated the eruptive sequences, whereas in the 1964 Shiveluch eruption it was probably the large earthquake at 07:07 that had triggered the structural failure. This, in turn, had released hydrothermal pressure in the system, producing a relatively small phreatic explosion. In the other volcanoes the collapses had released magmatic pressure, resulting in cataclysmic lateral blasts.

Devoted to a life of crime
Following its big effort in 1964 Shiveluch took a short break, but by 1980 it was back at work, forming another lava dome in the inner crater. That eruption lasted for two years, and was followed by another in 1984. Activity steadily increased through the late 1980s and into the 1990s, with the volcano constantly active – and growing – for six years until 1995.

Unaware of what is to unfold, volcanologists work on the upper slopes of Young Shiveluch (above) on 12 August 1986. On the following day, and with little warning, the dome exploded (below) and the area where they had been working was hit by a pyroclastic surge. As the photographer wryly commented, “Safety helmets would not have been much use.” (Photos by Alexander Iv. Malyshev via KVERT website)

Shorter periods of activity in the late 1990s were then replaced by sustained activity that began in August 1999, and which continues to this day. This period of near-continuous eruption has been punctuated by some major episodes, most notably that of February 2005. The dome complex now stands at around 2,500 metres above sea level, just below the peak of Young Shiveluch (also called the Fourth Summit) at 2,763 metres.

A threat to society?
Unlike many dangerous volcanoes, which seem to have attracted sizeable populations around them, Shiveluch represents only a limited danger to humans because there are thankfully few people living nearby. However, the small town of Kliuchi, 50 km distant, is at major risk from ashfall, and its soils show evidence of significant falls from past eruptions. This town is home to the volcanic observatory that watches the mountain and the Kliuchevskaya group (it also has a military airfield serving the Kura ICBM impact test range to the north of Shiveluch). The small coastal town of Ust-Kamchatsk at the mouth of the Kamchatka River is also under some threat from Shiveluch, and there is some evidence that the larger events (including that of 1964) have had some global reach.

Shiveluch’s main irritation, though, is to air traffic. KVERT seems to have the volcano on a permanent orange alert, and explosive eruptions routinely send ash clouds to 8,000 metres and above, including one earlier this year that nearly topped out at 10,000 metres. Most of the traffic in the region is flying above this level as it heads to Japan and other Far East destinations from Europe and the US. Nevertheless, Shiveluch does have the potential to pump ash up to 20,000 metres or so, where it would severely hamper air operations over a wide area.

Looking up from the mouth of the 1964 crater and the smouldering dome is growing well 30 years later. The ‘step’ in the foreground was formed by large slide-blocks coming to rest at the end of the 1964 collapse. (Alexander Belousov)

It seems that Shiveluch will continue to follow what appears to be a well-established pattern of behaviour (a dangerous assumption to make with volcanoes, of course). Dome-building is the name of the game, leading to an eventual catastrophic collapse every few hundred years, with the interval appearing to be shortening. A ‘best-guess’ estimate of when the next major collapse may occur, based on historic behaviour and dome-growth rates, points to around 2350/2550.

Along the way there will be numerous eruptions with heavy ashfall, pyroclastic flows, lahar formation and block-and-ash flows, accompanied by less-than-catastrophic structural failures and minor landslides. According to analysis, the delivery of magma to the wide chamber that underlies the structure is estimated at a whopping 36 x 10⌃6 tonnes per year, a considerably higher figure than for other volcanoes in the region.

Community service
By most criteria Shiveluch is bad to the bone, but even the worst offender has at least one redeeming feature. In a 1997 paper a team of Kamchatkan volcanologists stated that: “We tephrochronologists love Shiveluch dearly because its numerous ashfall layers can be traced over vast territories, and thus serve as excellent markers in Holocene studies, including dating of other volcanic deposits and landforms, tsunami and landslide deposits, river and marine terraces, archaeological sites etc.” Ash layers from single eruptions have reached over 400 km from Shiveluch, and over 100 eruptions in the Holocene period have left their individual tephra/avalanche signatures at distances of greater than 10 km from the volcano.

A north-orientated false-colour ASTER image from the Terra satellite on 25 February 2012 highlights the huge, south-facing horseshoe-shaped caldera formed by the 10,000 BP collapse of Old Shiveluch, as well as the much smaller crater of similar shape in which the dome currently grows. The light brown staining leading away from the cone to the southeast is ashfall on snow, and the dark brown patch near the bottom right corner is the deposit from a recent pyroclastic flow that reached around 8 km from the vent. (NASA)

Shiveluch has also played its part in the development of sensor fusion techniques for monitoring volcanoes. In August 2005, while Shiveluch was in a period of rapid dome growth following an explosive eruption in late February, US scientists flew over the volcano in a helicopter, gathering high-resolution thermal images with accurate spatial references. The data gathered revealed a crease structure at the centre of the dome, and a crescent-shaped high-temperature zone leading away from it.

While this imagery gave scientists useful immediate evidence concerning the nature of silicic lava dome growth, the heliborne thermal imager data was also compared with that from long-range ground cameras, and with images from the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) space sensor. By fusing imagery from all three sources, scientists gained a greater understanding of the thermal patterns in the dome, and gained another valuable technique for the study of other domes, notably the ability to estimate rates of extrusion.

Shiveluch looms over the wide Kamchatka river valley in a recent view. (Elena Klimenko, distributed by EGU under a Creative Commons licence)

Why is Shiveluch so active?
Here I run completely out of knowledge, but a look at the map shows that Shiveluch stands very close to the triple junction of Pacific, Okhotsk and North American plates. It is the subduction of the Pacific under the Okhotsk that is the principal driver of volcanism in Kamchatka, as well as the source of several tsunami-inducing M9+ ‘megathrust’ earthquakes in the region (including, of course, that which recently struck Japan). Might it be possible that the lesser subduction effects of the Okhotsk/North American plate boundary* might complicate matters at the northern end of the main Pacific/Okhotsk boundary, and give Shiveluch just that extra bit of magmatic ‘oomph’?
(*the nature and very existence of this plate boundary remains the subject of some debate)
Certainly Shiveluch’s rocks are of a subtly different make-up to those of the Kliuchevskaya group to the south. Apart from two medium-silica tephra-producing eruptions around 3,600 and 7,600 BP, Shiveluch’s products are typically high-silica, medium-potassium andesites, although they are close in composition to some adakite forms (named after an island in the Aleutian arc), exhibiting similar REE (rare earth element) traces, such as high strontium/yttrium and lanthanum/ytterbium ratios. Compared with other medium-potassium andesites from Kamchatka, those from Shiveluch also have higher chromium, magnesium and nickel contents.

Acknowledgments: Information for this article was drawn from a number of sources, but I must cite Alexander and Marina Belousov, and their colleagues, for the research papers that form the basis for much of this article. Errors are, of course, my own.

Many additional images of Shiveluch’s recent activity can be viewed here: http://www.kscnet.ru/ivs/kvert/current_eng.php?name=Sheveluch

UKVIGGEN

Update 10.10.2012

Topey says: October 10, 2012 at 09:56

Wonderful NASA photo of the ash plume from Shiveluch:

http://earthobservatory.nasa.gov/IOTD/view.php?id=79353&src=eoa-iotd

ukviggen says: October 10, 2012 at 11:15

Thanks Topey – great pic. Glad to see my old mate is still up to his bad-boy ways!

And here’s the moment it went boom. All over very quickly judging from the webcam archive (at the link on the photo).

Webcam image

http://i45.tinypic.com/vxkklt.jpg