Grantee name: Alexander Belousov
Grant number: 7697-04
Attached is RESEARCH REPORT for the above referenced grant number.
"Direct sampling of volcanic cloud with the goal to determine real grain-size distribution of pyroclastic particles"
Our 18-days-long expedition to the erupting Karymsky volcano (Kamchatka Peninsula, Russian Far East) was focused on the collection of detailed observational and geological data about explosive eruptions. Main goal of the work was to investigate grain-size distribution and concentration of the pyroclastic material (“volcanic ash”) in eruptive clouds. This problem is one of the very important of volcanology. Without knowing that it is impossible to understand processes of magma fragmentation during volcanic explosions, to calculate precisely erupted volumes of magma, to predict effects of eruptions on climate, and to estimate volcanic danger to aircrafts. Our field work included detailed observations of volcanic explosions combined with simultaneous sampling of the erupted pyroclastic material. Highlight of the expedition was testing of a new method of direct sampling of eruption clouds using tethered balloons filled with helium. During the field work the Karymsky volcano produced regular mild ash outbursts of vulcanian type from the summit crater. Explosions occurred every 2 - 50 min, ejecting incandescent bombs up to 0.5 km high, and convective ash cloud rose up to 2 km above the crater (3.5 km a.s.l.). A number of samples of fresh ash were collected over large area around the erupting volcano. Especially important that sampled pyroclastic material was produced by explosions which were observed and their characteristics documented with video footage. Additionally to the studies of the modern volcanic activity, we have studied outcrops of prehistoric pyroclastic deposits around the volcano in order to reconstruct character of its activity in the past.
Processing of the collected data will allow to establish grain size distributions and concentration of pyroclastic particles in eruptive clouds of Karymsky volcano.
Our work has been devoted to investigation of processes of explosive volcanic eruptions. Explosive eruptions are relatively rare and dangerous events and the available observational data are scarce and commonly not satisfied because were obtained from long distances. Most of currently available data about processes occurring during explosive eruptions represent reconstructions based on investigation of old pyroclastic deposits, formation of which was not directly observed.
The reported 18-days-long expedition (July 2005) was focused on collection of detailed observational and geological data about explosive eruptions. Main goal of our study was determination of grain-size distributions and concentrations of pyroclastic material in volcanic clouds formed as a result of volcanic explosions. This problem is one of very important in volcanology (Sparks et al. 1997). Without knowing that it is impossible to understand processes of magma fragmentation in the course of volcanic explosions, to calculate precisely ejected volumes of magma, to predict effects of eruptions on climate, and to estimate volcanic danger to aircrafts (Kennett & Thunnel 1977; Handler 1989; Przedpelski & Casadevall 1994; Alidibirov & Dingwell 1996; Belousov et al. 2002).
Our work included detailed observations of volcanic explosions and simultaneous sampling of the erupted pyroclastic material. In the field we used both a conventional method of sampling of volcanic ash deposited on the ground surface as well as tested a new method of direct sampling of eruption clouds using tethered balloons filled with helium.
Karymsky (1540 m high) is located in the Eastern Volcanic Belt of Kamchatka Peninsula, 125 km to the north-east from the main town Petropavlovsk (fig. 1). This is typical stratovolcano nested inside circular caldera 4 km in diameter (fig. 2).
Karymsky is one of the most active volcanoes in the world. It is characterized by frequent, steady, long-term explosive eruptions of magmas of andesitic – dacitic compositions (Fedotov 1991). Each eruption commonly lasts tens of years and consists of frequent explosions of vulcanian type occurring in the summit crater. Periodically explosive activity is accompanied by outpouring of viscous lava flows. In the 20th century eruptions occurred in 1908-1912, 1915, 1921-1925, 1929, 1932-1935, 1938-1947, 1952-1957, 1960-1967, 1970-1979, and 1982 (Gushenko 1979). Last eruption of the volcano (the one we have studied) started in 1996 and continues until now.
Fig. 1. Kamchatka Peninsula with indicated locations of the main city Petropavlovsk and Karymsky volcano.
Fig. 2. Edifice of Karymsky volcano nested inside the old caldera. View from helicopter from the SW. Photo A. Belousov.
Karymsky was selected as a target of our research because its explosive activity is very steady and thus rather predictable. That allows to work very close to the exploding volcano in relatively safe conditions. Also important is that the volcano is very convenient to conduct field works – it has rather small edifice (relative elevation of the crater 700 m) and area around the volcano is easily accessible.
Two researchers and two volunteers participated in the field work (fig.3).
Alexander Belousov, PhD and Marina Belousova, PhD. Both are senior scientists of the Institute of Volcanology and Seismology, Petropavlovsk-Kamchatsky, Russia.
Vsevolod Panov, physicist, assistant professor, State University of Kamchatka and Andreas Auer, graduate student, geologist, University of Freiberg, Germany.
Fig. 3. Participants of the expedition (from left to right): Marina Belousova, Alexander Belousov, Andreas Auer, Vsevolod Panov. Karymsky volcano in the background.
To get to and out of the filed with all the necessary equipment as well as to transport heavy cylinders with helium around the volcano we hired helicopter Mi 8 (fig.4), which was the only transport suitable for the area (mountainous terrain with no roads and few trails). Payment for the helicopter composed the most significant part of the expedition budget.
On the volcano the group was based in a house (former seismic observatory of the Institute of Volcanology), which is located on a distance 3 km from the crater. During launches of the scientific balloons we used also another, smaller hut on a distance 1.5 km from the crater.
Fig. 4. Helicopter Mi 8 landing at Karymsky. Photo A. Auer.
Fig.5. Expedition equipment packed inside the helicopter. Photo A. Auer.
During the field work Karymsky produced regular weak and mild ash outbursts of vulcanian type from the summit crater, which are common for the volcano. Explosions occurred every 2 - 50 min, ejecting incandescent bombs up to 0.5 km high, and convective ash cloud rose up to 2 km above the crater (3.5 km a.s.l.) (fig. 6). During daytime no incandescent material was visible, but in nighttime red-hot bombs and glowing was observed during the explosions (fig. 7).
Fig. 6. Erupting Karymsky volcano. Strongest of the observed explosions. Volcanic cone is covered by dust produced by falling bombs. Height of the eruption column is about 2 km. View from the south. Distance to the volcano 3 km. Photo A. Belousov.
Fig. 7. Glowing and traces of volcanic bombs of Karymsky during nighttime explosions. Photo A. Belousov.
Some explosions ejected mostly white steam with little ash. Between explosions only weak fumaroles were visible in the crater. Explosive activity was associated with growth and periodic destruction of small lava dome in the summit crater of the volcano (fig. 8). The eruption caused frequent ashfalls around the volcano, which occurred in different sectors around the volcano depending on wind direction.
Fig.8. Crater of Karymsky at July 2005. Small lava dome is extruded from the vent. The observed explosions occurred from the surface and margins of the dome. Photo A. Belousov.
We conducted continuous visual observations of the eruption when weather permitted to see the crater. Time, height of the eruption clouds and relative concentration of ash were registered. Video footages of many of the witnessed volcanic explosions have been made in order to document characteristics of the explosive eruption. Processing of footages allows determination of several important parameters like initial velocity of the ejected material, duration of the explosive process etc. Later, working in the lab, we are going to use the obtained data to find a link between characteristics of the collected pyroclastic material and characteristics of the explosive activity.
Violence of the explosions and their frequency gradually fluctuated with time during the field work. In order to understand patterns of the volcanic activity, we plotted heights of the eruption clouds versus time of the explosion. The plots of the activity (fig. 9) allowed us to do short-term forecasts of intensity of the eruption directly in the field and helped to make decisions about launch time of the scientific balloons. Seismicity of the volcano, provided by local telemetric seismic station, was used as additional source of information about the level of volcanic activity (volcanic explosions produce peculiar type of earthquakes). Seismic information was especially useful in periods when Karymsky was obscured by clouds.
July 11, 2005
July 11, 2005
July 13, 2005
July 13, 2005
Fig.9. Examples of plots of explosive activity of Karymsky volcano: on horizontal axis – time (hours : minutes), on vertical axis – height of eruptive cloud above the crater (meters).
Main efforts during the field work were aimed on collection of samples of fresh ash in the process of its transportation in the eruption clouds off the source (crater). That was done in two different ways.
(1) Conventional method. We installed multiple sampling boxes around the volcano on different distances from the crater. Periodically we visited the boxes (only those located downwind from the crater, where ash falls have occurred) and collected the accumulated pyroclastic material. Using the data about the amount of ash accumulated in the sampling box, its grain-size characteristics and the time during which the material was accumulated, we will be able to calculate a number of parameters: the rate of accumulation of ash in different sectors from the volcano; how quickly grain-size parameters of fallout ash change with distance from the volcano etc. Special efforts were made to sample ash deposited from single short-lived explosions. To do that some of the sampling boxes were continuously monitored and samples were collected each time the ash was deposited.
(2) New method - direct sampling of volcanic clouds using scientific balloons. The method was designed by the principle investigator of the project and applied in the first time at Karymsky in 2003 (Belousov, Belousova 2004).
To carry the sampler into eruptive cloud we used tethered balloons filled with helium. Two types of balloons were used: Disc-shaped plastic balloon (commercially produced by Floatograph Technologies, Marion, IN) and standard latex weather balloon placed in nylon protective shell (fig. 10).
Fig.10. Process of inflating of the balloons with helium (3 km from the volcano). Disc-shaped plastic balloon (red) commercially produced by Floatograph Technologies, Marion, IN and standard latex weather balloon placed in nylon protective shell (yellow). Photos of A. Auer
The balloons contained about 6 and 3 cub.m. of helium accordingly. The balloons were inflated with helium from cylinders which we brought with us from Petropavlovsk. We inflated the balloons on a rather long (about 3 km) distance from the volcano (fig.10), and then walked with them to the location of launching site (fig. 11). We could not inflate the balloons directly at the launching site because helicopter was not able to land at the foot of the volcano, where thick layer of friable ash have been accumulated. Launching sites were selected depending on wind direction and intensity of volcanic activity at the time. The tether was rolled in and rolled out with a motor winch (fig. 12).
Fig. 11. Transportation of the scientific balloons to the launching site. Photo of A.Belousov
Fig.12. Operating the motor winch rolling the tether. Photo of M. Belousova.
Two basic schemes of sampling were used:
(1) launch from location downwind from the crater (simple lifting of the balloon in the eruptive cloud drifting above) and
(2) launch from upwind location (when wind tilted the balloon toward the crater).
Fig.13. Two principal schemes of sampling of volcanic cloud from downwind (1) and upwind (2) locations with tethered balloons (explanations in the text).
In the first scheme, sampling device was working in already cooled and strongly diluted part of the eruptive cloud. Conditions inside the cloud were not destructive for the balloon, thus the sampler was directly attached to it. The low temperature sampler represented a sticky plastic film to which particles from the eruptive clouds were able to adhere. Totally 6 launches were made during the expedition with the maximum achieved altitude about 2,5 km above the launching site and 1,8 km above the crater (3400 a.s.l.). A number of samples from low concentration part of the eruption cloud have been collected.
In the second scheme the eruptive cloud was thought to be still hot and containing high concentration of large strongly abrasive particles. Thus the balloon in this configuration ought to fly higher than the eruptive cloud, and sampler was hanging down from the balloon on a long (about 500m) metal line. The high temperature sampler was like a box 0.5-liter in volume made of metal foil. It was designed to work like a mouse trap (fig. 14).
Fig.14. Sketch of high-temperature sampler.
Triggering mechanism represented a plastic filament, which kept the lid of the sampler in opened condition. When the sampler entered hot cloud, the filament melted, allowing the lid to be closed. For launches from upwind locations we used two balloons connected with tether (fig. 13 and 15).
Fig. 15. Launch of the tethered balloons from upwind location (when wind tilted the balloon toward the crater). Photo of M. Belousova
Each launch we adjusted the length of the connecting tether, depending on the wind strength (the stronger wind, the shorter connecting tether). That allowed us to place the sampler directly above the crater. Unfortunately in the course of one of the launches the balloons unexpectedly entered high speed wind at the altitude of the crater. That caused failure of the tether and the balloons were lost. Thus high temperature and high concentration part of the eruptive cloud was not sampled. Despite of that our experience has demonstrated principle validity of the method for sampling of proximal regions of eruption clouds. The conducted launches allowed us to receive valuable experience in operating of balloons above erupting volcano. Our experience has shown that main danger is tether breaking in strong wind. We understood how we should improve the sampling equipment.
As a result of our work a number of samples of fresh ash were collected over large area around erupting volcano. Especially important that many of these samples were collected from explosions which were observed and their characteristics documented with video footage. Additionally to the studies of the present time volcanic activity, we have studied outcrops of prehistoric pyroclastic deposits around the volcano in order to reconstruct character of its activity in the past.
Processing of the collected data will allow to establish grain size distributions and concentration of pyroclastic particles in eruptive clouds of Karymsky volcano. Investigation of morphology of the collected pyroclastic particles under scanning electron microscope (SEM) will allow to make conclusions about mechanism of fragmentation processes, which operated during the studied eruption.
Main problem during the field work was very unstable weather characterizing by strong winds, which frequently changed their directions. That was the main obstacle for launches of the scientific balloons, and eventually led to the tether failure and lost of the two balloons.
Additional problems were connected with excessively curious brown bears, which used the same trails as we did as well as destroyed our equipment for sampling of falling ash several times.
First of all will be very important to get samples from the most proximal part of the eruption cloud – the goal which was not achieved during the reported expedition. Secondly, in the reported expedition we have studied vulcanian type of explosive eruptions. Will be worth to continue similar detailed investigations of other types of explosive eruptions. Especially important to study explosions associated with growing volcanic domes – one of the most dangerous and poorly predictable type of volcanism.
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