Situated in the central part of the Big Kurile Chain, is a desert island called Matua (52 km²), which means "small burning bays". The main natural object of note here is a 1,446 m high active vol-cano-Sarychev* Peak-discovered in the 18th century by Russian Cossacks, which had supposedly been formed 40-50 thous years ago. Only in the 20th century it erupted 7 times-in 1923, 1928, 1930, 1946, 1954, 1960 and 1976. During the eruption of 1946, the volca-no threw its rocks 7-8 km away from the crater, and ashes reached Petropavlovsk-Kamchatsky. In 1976, there were observed lava flows. But the most powerful eruption of Sarychev Peak volcano for the whole peri-od of observations in Kamchatka started on June 12, 2009.

In the course of an active phase of eruption (June 12-16), scientists registered 12 explosions (9 of which were powerful) with a discharge of incandescent detrital rock. As a result of the most powerful explosion, the lava plug in the crater that formed in 1976 had collapsed and a steam and gas cloud with ashes, an increased content of silt and sulfur dioxide rose to a height of 11-16 km over the ocean (according to some data up to 20 km), covered 3,000 km   of the territory, and reached  Southern Sakhalin, Khabarovsk Territory and a central part of the Pacific Ocean, thus temporarily breaking off air commu-nication between Alaska and Japan.

Then the volcano discharged scoria, forming some pyroclastic streams (with a temperature of up to 500-600°C). The volume of erupted material made up approximately 0.2-0.3 km .

Thanks to efficient observations conducted through TERRA, NOAA and MTSAT satellites, scientists of the RAS FEB Institute of Marine Geology and Geophysics (Yuzhno-Sakhalinsk) managed to register all main phases of the eruption. It became clear: surface studies should be organized to analyze this unique planetary phenomenon. Thus, On June 23, 2009, an expedition formed by scientists of the said Institute and employees of the Institute of Automatics and Management Problems, Pacific Institute of Oceanology named after V. Ilyichev, and Pacific Institute of Geography left for Matua Island. Results of their work are analyzed in the article by Boris Levin, RAS Corresponding Member and Director of the Institute of Marine Geology and Geophysics, Alexander Rybin, Cand. Sc. (Geol. & Miner.), from the same Institute, and Ivan Melekestsev, Dr. Sc. (Geol. & Miner.), from the RAS FEB Institute of Volcano-logy and Seismology (Petropavlovsk-Kamchatsky), published in the RAS Bulletin magazine.

* Admiral Gavriil Sarychev (1763-1831)-Russian hydrographer, honorary member of the St. Petersburg Academy of Sciences (elected in 1809).-Ed.

The scientists had only a few days for field works- from June 26 till July 3. Using portable G PS-naviga-tors, the participants of the expedition drew a map of pyroclastic streams. As it turned out, their total onshore area makes up 8 km², but the majority of them reached the sea level and even the submerged part of the island. Echo sounding method helped the scientists gather data clearly showing disperse exhausts of gases in deep places and suspension of hydrothermally altered rock.

Having studied cross sections of three pyroclastic streams on Matua, the specialists have established: there are inclusions of scoria, volcanic bombs and ashes. The erupted rocks classified in the course of field works as andesibasalt deposits are spread over the island rather unevenly: their maximal quantity (thickness of deposits is up to 15-20 m) is localized within the limits of the central cone of Sarychev Peak and its foot-here red-hot "rivers" ran from the top of the volcano to the coast. There they were blocked by layers of volcanic ashes (28-30 cm) and scoria (1-2, in rare cases 3-5 cm) with a filler of irregular coarse sand with gravel parti-cles. Samples of all rocks were taken for laboratory studies.

The comparative analysis of space photographs taken by spectroradiometer ASTER (TERRA satellite) was carried out that showed expansion of the island territo-ry almost by 1.4 km² owing to the discharge of scoria. As if the volcano that started to erupt on the day of nation-al holiday, the Day of Russia, presented this small piece of land as a gift to "compatriots".

For a week, the participants of the expedition studied fumaroles*, measured temperatures of rocks and gas emission phase. In places where pyroclastic streams lay (on June 28 their temperature in the northern part of

* Fumarole (from Italian fumo-smoke)-a source of hot gases in craters and on the slopes of volcanoes and in the crust of cooling lava streams.-Ed.

the island made up 420°C at a depth of 30 cm), soil and vegetable cover was fully eliminated and the landscape changed significantly.

Fortunately, the eruption of the volcano did not affect the autonomous station of continuous G PS-observations equipped in 2007 in the southern part of Matua in order to study present-day movements and deformations of the earth surface. Two control points for periodical monitoring were not damaged either. So, today nation-al scientists have all necessary data on the period pre-ceding the event and its active phase (June 12-28, 2009). By the way, Yuzhno-Sakhalinsk volcanoligists warned their colleagues working at the Alaska Volcano-logical Observatory about the beginning of eruption on Matua as early as June 11, 2009.

It stands to reason that all "hot" materials obtained on the island should be studied in detail. But it is clear even now: Far Eastern scientists gathered unique data that will enable them to assess the scale of movements in the earth surface triggered by activation of Sarychev Peak.

B. Levin, A. Rybin, I. Melekestsev, Russian Territory Expanded After Recent Developments in the Sakhalin Region, "RAS Bulletin " magazine, Vol. 80, No. 1, 2010

Prepared by Yevgeniya SIDOROVA